Algae for Tilapia

• Plankton are organisms (animal or plant) that live in the water and cannot swim against a current; zooplankton and phytoplankton.
• Algae includes brown and green algae (planktonic or attached; single-celled or multicellular), and diatoms (planktonic, attached or motile; single-celled or colonial).
• Blue-green algae (planktonic or attached; single-celled or colonial) are bacteria with photosynthetic capacity; cyanobacteria (cyano = blue).

Algal growth

The favourable pH range for plankton growth ranges between 6.5 and 7.5. Acidic conditions favor chlorophytes (green algae) while alkaline condition fosters nitrogen-fixing cyanobacteria.[14] High salinity favors green algae (plus Spirulina) while low salinity fosters cyanobacteria. In phytoplankton-based recirculating systems, algae may rather be limited by dissolved organic carbon availability rather than by nitrogen or phosphorus.[15] Chlorophyta are most ammonium tolerant, followed by Cyanophyta.[16] Chlorella vulgaris has higher lipid contents than Scenedesmus abundans and Monoraphidium minitum, which was also reflected in their predator, Brachionus calyciflorus. [17] Organic matter of manure (eg chicken manure [18]) hardly contributes directly to fish growth; only indirectly through carbon incorporated in algae.[19] Most fertilized fish ponds with dirty green water have more than 242 mg phytoplankton biomass per L water.[20] Diatoms are less dependent on trace elements than other algae.[21]

Diatoms

Diatoms may often be present as a brown, slippery coating on submerged stones and plants, and may stream along with the current in a river or stream. Diatoms are microscopic unicellular algae, all consisting of the same basic parts; nucleus, cytoplasm, plasma membrane, and the transparent cell wall.[22] Diatoms may form colonies in various shapes; filaments or ribbons (e.g. Aulacoseira granulata), fans (e.g. Meridion), zigzags (e.g. Diatoma vulgaris), or stars (e.g. Asterionella). Diatoms are the dominant primary producers in many ocean regions. They capture solar energy and CO₂, and produce oxygen. Diatoms are mainly photosynthetic, containing various prigments (xanthins, carotenes), and they efficiently use carbon and nitrogen from their environment.[23] Diatom cells are enclosed within a hard but porous peculiar cell wall made of protective silica (hydrated silicon dioxide), called a frustule. These frustules are usually nearly bilaterally symmetrical; one valve just fitting inside the other. Thus silicon is the major limiting nutrient, which is exclusively specific for diatoms.[24] Diatom dominance may be directly related to the availability of silicic acid.[25] The biogenic silica in diatom cell walls may facilitate the conversion of bicarbonate to dissolved CO₂.[26] In tropical conditions, diatom abundance is enhanced by increases in silica and ammonium, and by declines in conductivity, total phosphorus and water temperature.[27] Diatoms are high in lipids and amino acids.[28]

Most diatoms divide to produce two daughter cells, with each cell keeping one of the two halves and growing a smaller half within it. Thus the average size declines due to division. Once a minimum size has been reached, auxospores are produced. Auxospore production is usually associated with meiosis and sexual reproduction. The auxospore cell wall lacks the siliceous frustule, and swells to the maximum frustule size. Once big enough, the cell may eventually start dividing again. In various important biological characteristics (including sexuality) the similarities between flowering plants and diatoms are striking.[29]

• Mostly only male centric flagellates are motile (and some Nitzschia species, such as Nitzschia sigma)
• Benthic diatoms live as surface films at the water-sediment interface. (eg Synedra ulna)
• Epiphytic diatoms grow on plants (macrophytes)
• Periphytic diatoms live on the surface of submerged plants and other underwater objects, such as rocks.(eg Nitzschia sp. 1)
• Meroplanktonic diatoms are part of plankton during the larval stage of their life and spend their adult lives in between the plankton on the reef (eg Melosira species).
• Epipelic algae grow on sediment (eg Rhopalodia species)
• Epilithic diatoms grow on rocks / stones

Diatoms may be collected from any stream or pond. Fill a glass jar with mud and water, and wrap it in black paper. Expose it to full sunlight. The diatoms will emerge at the surface in a foam within 24 hours. How to prepare diatom slides Cultivated diatom numbers may typically increase 10-fold in the span of 10 days.[30]

Feeding

Ceriodaphnia © micromagus.net

Tilapia start feeding shortly before dawn and feed continually (but most intensively between 12:00 and 18:00[31]) until about dusk. They do not feed during the night.[32][33] Tilapia (Oreochromis niloticus) may effectively control algal blooms in eutrophic waters.[34] Planktonic plants and animals make up the bulk of the diet under natural conditions.[35] Zooplankton (animal) does not exceed 1.5% of total stomach contents [36], with predation pressure being the greatest on Ceriodaphnia reticulata (small water fleas that feed on small algae) [37], due to low escape probabilities for (Cerio)daphnia compared to copepods (small crustaceans).[38] Phytoplankton (plant plankton) may contribute over 30% by volume of stomach contents of Oreochromis niloticus.[39] Small Tilapia rendalli consumed more diatoms than larger individuals.[40] Oreochromis niloticus feeds mainly on zooplankton until 5 cm long, and mainly on phytoplankton as it grows older. In small fish (<75 g.) Bacillariophyceae are the main phytoplankter, and in larger fish Chlorophyceae are the main phytoplankter.[41] Tilapia (Sarotherodon melanotheron) shift from visually feeding on zooplankton when juveniles to mostly filter feeding on phytoplankton when adults [42], consuming less Microcystis and Scenedesmus as they grow bigger.[43] Blue-green algae (colonies of photosynthetic bacteria; cyanobacteria) are common components of the Tilapia diet. In the stomach of Tilapia nilotica the cells of blue-green algae are lysed by high concentrations of acid (pH 1.4–1.9). After lysis, cell contents are digested in the intestine (by pepsinogen, a pancreatic α-amylase, trypsin, chymotrypsin and esterase activity). Acid is secreted in relation to feeding. Acid is not secreted by stressed fish.[44] Filtration rates of algae increases linearly as water temperature increases from 17°C to 32°C.[45]

The main species of algae found in Oreochromis niloticus stomach belonged to Cyanophyta, Chlorophyta, Bacillariophyta and Euglenophyta.[46] The most frequent species represented in Oreochromis niloticus stomach are Anabaena sp., Merismopedia eleganse, Microcystis aeruginose, Nodularia harveyana and Oscillatoria sp. (Cyanophyta), Cerasterias sp., Chlorella spp., Crucigenia sp., Pediastrum spp., Scenedesmus spp. and Tetraedron sp. (Chlorophyta), Amphora ovalis, Cocconeis placentula, Cymatopleura solea, Cymbella cistula, Gyrosigma attenuatum, Melosira granulata, Navicula spp., Nitzschia spp., Pinnularia spp., Serurella sp. and Synedra sp. (Bacillariophyta) and Euglena and Phacus spp. (Euglenophyta).[47] The most frequent genera represented in fish (Oreochromis niloticus) stomach in all sizes were Anabaena, Anabaenopsis, Coleospharium, Merismopedia, Microcystis, Nodularia, Oscillatoria, Spirulina (Cyanobacteria), Actinostrum, Chlorella, Closterium, Coelastrum, Eudrina, Pandorina, Pediastrum, Scenedesmus, Shereoderia, Staurastrum (Chlorophyceae), Amphora, Cocconeis, Cymatopleura, Cymbella, Gyrosigma, Melosira, Navicula, Pinnularia, Synedra (Bacillariophyceae) and Euglena and Phacus (Euglenophyceae).[48] Botryococcus sp. (green algae)[49][50] and Melosira (a diatom; Bacillariophyceae)[51] may also be major food items in the diet of Oreochromis niloticus.

Selective feeding

Uroglenopsis © John DuFresene

Spirulina platensis © http://mcc.nies.go.jp/

Ceratium © Y. Tsukii

Tilapia feed selectively on large algae, mainly cyanobacteria and diatoms [52] and select more for diatoms than for the blue-green algae (cyanobacteria).[53] Oreochromis niloticus may select only Cyanophyta and Euglenophyta (unicellular flagellate protozoa), with occasional Bacillariophyta (diatoms).[54] Oreochromis niloticus may select Cyanophyta and sometimes select Bacillariophyta and Euglenophyta.[55] Blue tilapias (4.3 to 18.7 cm long) selectively feed on particles larger than 25 μm.[56] Nile tilapia is particularly effective in filtering the larger particle size taxa.[57] Larger phytoplankton (plant plankton) are being filtered proportionally more than the smaller phytoplankton, and cyanobacteria (in 100% of fish[58]) more than green algae (Scenedesmus, Ankistrodesmus, Tetraedron).[59] Tilapia aurea (Blue tilapia) favour Uroglenopsis sp. (cells forming hollow spherical colonies, > 400 μm diameter), Ceratium sp.(dinoflagellate (the least ammonium tolerant [60]), 310 μm long, 58 μm wide; optimum salinity 10 ppt[61]) and Keratella sp. over (small-sized algae) Rhodomonas sp., Chrysochromulina sp., Chlamydomonas sp., Cyclotella sp. and (zooplankter) Diaptomus sp.[62] Oreochromis niloticus juveniles prefer Elodea canadensis over Potamogeton pectinatus and Spirodela polyrhiza. Myriophyllum spicatum was the least preferred.[63]

Oreochromis niloticus prefer to prey on the large size diatoms, such as Melosira granulata, Synedra ulna, Cyclotella ocellata and Cyclotella operculata.[64] Astrionella sp. and Rhopalodia vermicularis (bacillariophytes) and Peridinium sp. (dinophyte) were selected by both wild and pond-cultured Oreochromis niloticus. Lake fish particularly selected Astrionella sp., Aulacoseira (Melosira) nyassensis, Navicula sp. (which grow on sediment[65]) and Rhopalodia vermicularis (bacillariophytes). Pond fish particularly selected Ankistrodesmus falcatus (chlorophyte), Lyngbya circumcreta (cyanophyte) and Nitzschia acicularis.[66] Oreochromis niloticus may prefer Spirulina laxisma and Nitzschia accicularis the most. The least preferred food items may be Lyngbya circumcreta, Microcystis aeruginosa and Pediastrum simplex.[67]

Brachionus plicatilis

Brachionus plicatilis

Akashiwo sanguinea © SERC

Brachionus plicatilis is an important food source for larval fish. Brachionus plicatilis is also the most successful species of zooplankton used to control unicellular algal contaminants in Spirulina mass cultures even under conditions adverse to the growth of Spirulina (very low bicarbonate).[68] Brachionus plicatilis is a rotifer / zooplankton associated with saline, alkaline waters.[69] Brachionus plicatilis may thrive in water with pH fluctuating from ~7 to 9.5 pH. (total P > 48 µg/L; nitrate-nitrogen > 80 µg/L)[70] It may be 123 to 292 μm long and 114 to 199 μm wide. Compared to temperature and salinity, strain is the most important factor determining size.[71] Maximum reproduction occurs between 30 and 34 C. Reproduction rate is similar in 25% and 33% seawater. Brachionus plicatilis may thrive in 0.5 to 30 ppt salinity (brackish) and may be 99 to 281 μm long and may weigh 0.18 μg. In contrast to female Brachionus rubens, fecund female Brachionus plicatilis do not attach to a substrate. [72] Adult Brachionus plicatilis may be 213 to 315 μm long. Optimum salinity may be 18 ppt. The most common feed types are single-celled algae.[73] Brachionus plicatilis may (together with Nitzschia spp) survive in 10 pH, high calcium carbonate and 91 ppt salinity.[74]

Brachionus plicatilis may be mass cultured on Akashiwo sanguinea (Gymnodinium splendens / nelsoni), an unarmored (naked) dinoflagellate. [75] Akashiwo sanguinea is a mixotroph, as it is both photosynthetic and feeds on cyanobacteria and nanociliate populations (tiny protozoans)[76], which may be algivores.[77] It may form subsurface chlorophyll maximum layers in the water, which is consumed by larval fish.[78] This may be in response to a relative nitrate deficiency during the light period.[79] Dinoflagellates prefer calm water column situations; small-scale turbulence may diminish dinoflagellate growth and cell division, but may also increase cell size.[80] Akashiwo sanguinea may thrive in brackish conditions.[81] Coastal Akashiwo sanguinea bloom events may be supported by elevated urea.[82] Brachionus plicatilis grazes on Spirulina platensis, particularly on large, dense filaments.[83]

Keratella

Keratella © Michael Plewka

Young Oreochromis niloticus mainly feed on zooplankton until ~5 cm long.[84] Keratella sp. are relatively small (~100 μm long) 'wheel animals' / rotifers / zooplankton. Growth may be optimal at 24°C temperature and 20 ppt salinity. Fecundity may be optimal at 0 ppt salinity.[85]

Keratella cochlearis may thrive in water with pH fluctuating from ~7 to 9.5 pH. (total P > 48 µg/L; nitrate-nitrogen > 80 µg/L)[86] Keratella cochlearis and Keratella quadrata are euryhaline and perennial (not seasonal).[87] Keratella cochlearis, Keratella americana and Keratella tropica are considered euryhaline (able to adapt to a wide range of salinities). Keratella hispida may thrive on 30 ppt.[88] Keratella tropicana may occur in shallow waters at 43 ppt salinity.[89]

Peridinium cinctum

Peridinium cinctum © Jacek

Peridinium species are large phytoplankton (30-70 μm diameter armoured dinoflagellates) that less efficiently take up nutrients than smaller species. At their advantage is the capacity to modify their position in the water column (in accordance with light and nutrient availability), that they are (because of their large size) inedible by most zooplankton, and their extremely low phosphorus requirements (C:P molar ratio is 460:1).[90] They may produce 2 to 3 times more organic matter than other alga.[91]

Tilapia (galilaea) favourably consume Peridinium cinctum.[92] Feeding rates of Tilapia galilaea and Tilapia aurea reach maximum values for zooplankton (animal plankton) and Peridinium cinctum.[93] Fingerlings fed experimentally on chlorophytes had lower growth rates compared with mosquito larvae, zooplankton and fresh Peridinium.[94] Growth rates of age-1 Tilapia galilaea on Peridinium may be 1–2% mean weight per day.[95]

When phosphorus is low, Peridinium has an advantage over other alga.[96] Peridinium aciculiferum may particularly produce toxins when deprived of phosphorus and in stationary phase.[97] Blooms of Peridinium gatunense (biomass > 100 g / m2) may change the color of the water to coffee brown in distinct patches and are associated with excessive oxygen super-saturation, and high phosphorus (> 0.05 mg/L) and nitrogen (> 1 mg/L).[98] Peridinium gatunense and Microcystis sp. are highly competitive.[99] Peridinium ponticum may thrive in 17 ppt salinity.[100] Peridinium cinctum is common below 20 ppt salinity.[101]

Cocconeis placentula

Cocconeis placentula © Proyecto Agua

Cocconeis placentula © 珪藻ギャラリートップへ

Oreochromis niloticus preferentially selects diatoms over cyanobacteria.[102] Cocconeis placentula is frequently represented in Oreochromis niloticus stomach.[103] Cocconeis placentula is a diatom that may be 9-68 µm long and 7-32 µm wide [104], or up to 98 µm long and 40 µm wide.[105] Cocconeis placentula thrives in moderately saline and moderately alkaline, shallow waters.[106] Cocconeis placentula readily attaches to substrates due to the secretion of adhesive substances.[107] Cocconeis placentula is very common in (brackish / freshwater[108]) eutrophic [109], benthic habitats, where it (solitary) attaches to rocks, macrophytes and algae. It is tolerant of moderate organic pollution, with var. euglypta being possibly more tolerant.[110] Cocconeis placentula may thrive in shallow waters at 6-29°C and 6.9-7.7 pH, with 0-2.5 ppt salinity, 3.0-4.1 meq/L alkalinity, 0.0-0.45 mg/L NH₄, 0.0-0.09 mg/L phosphates.[111] Cocconeis placentula may prefer elevated total phosphates.[112]

Cocconeis placentula var. euglypta is a bit smaller, but also attached solitary, and may survive in lakes with 40 ppt salinity [113] or brackish / freshwater.[114]

Cyclotella

Cyclotella ocellata © RedOrbit

Oreochromis niloticus prefer to prey on the large size diatoms, such as Cyclotella ocellata and Cyclotella operculata, which are Centrophycidae.[115] Cyclotella ocellata is cylinder-shaped and may have a diameter of 6 to 25 µm [116] up to 40 µm. (incl. C. krammeri and C. rossii) [117] and may be 6.3-16.5 µm long.[118] Cyclotella ocellata is sometimes considered to be planktonic (floating in the water)[119] or epiphytic (growing on plants). It may be considered oligosaline (0.5 to 5 ppt salinity) [120]p37), with a brackish-freshwater salinity optimum. [121]p194) Cyclotella ocellata may dominate in cold waters with low salinity and very little nutrients [122], but may also thrive in eutrophic waters [123], at high salinity and turbidity (in shallow waters) [124] and at higher temperatures (in diluted estuaries).[125] Alkalinity range is 80 to 190 CaCO₃ mg/L.[126]

Cyclotella operculata (5-43 µm diameter, <3 µm depth [127]) is considered planktonic [128] and may thrive at 7.9 to 8.4 pH (Cl 64 mg/L ; NH₃ 0.28 mg/L ; P 0.23 mg/L).[129] Cyclotella in general thrive in the oligo-mesotrophic range ('deficient' to moderate levels of dissolved nutrients, and high DO) [130], but also Cyclotella operculata may dominate in eutrophic (soft and hard) waters, at 27-33°C, 40-67 mg/L alkalinity, 0.5-2.5 mg/L phosphates and 0.2-0.8 mg/L nitrates.[131]

Cyclotella meneghiniana (15 µm diameter; benthic[132]) is favoured by high light penetration [133] and most abundant at high nitrate (4.6 mg/L). (ph 7.7 to 8.0)[134] Cyclotella meneghiniana may thrive in shallow water (<50 cm) at 908-1100 mg/L Na; 22-33 mg/L K; 7-8 mg/L Ca; 4-6 mg/L Mg; 3-4 mg/L SiO₂; 0.4 mg/L Fe; 45-48 SO₄; 674-830 mg/L Cl and 25.5-26.5 meq/L alkalinity (carbonates plus bicarbonates).[135]

Cyclotella pseudostellagera (8 µm diameter; euryhaline[136]) may thrive at low Cl (7 mg/L) and high P (59 mg/L, as PO₄^-), 023 mg/L nitrate, 0.26 mg/L NH₃.[137]

Cymbella lanceolata

Cymbella lanceolata © Chris_M

Cymbella lanceolata (aka Frustulia lanceolata, Navicula lanceolata) may be 60-220 µm long and 18-32 µm wide, is alkaliphilous (at pH > 7), not motile [138] and is widely distributed (Arctic, China to Brazil).[139] It is a shallow-water species [140]pE7) and grows solitary or attached (cell-to-cell) in bushy colonies in brackish / freshwater.[141] Cymbella lanceolata may thrive in shallow waters at 6-29°C and 6.9-7.7 pH, with 0-2.5 ppt salinity, 3.0-4.1 meq/L alkalinity, 0.0-0.45 mg/L ammonium, 0.0-0.09 mg/L phosphates.[142]

Diatoma vulgaris

Diatoma vulgare © Alamy

Diatoma vulgaris is 15-60 µm long and 8-12 µm wide and may develop in fresh and brackish water. It forms zig-zag colonies attached to the substrate by a mucilage pad. [143] Diatoma vulgaris is associated with Melosira species and may develop optimally in running water.[144] Diatoma elongatum may thrive in water with pH fluctuating from ~7 to 9.5 pH. (total P > 48 µg/L; nitrate-nitrogen > 80 µg/L)[145] Diatoma vulgaris is considered to be mesotrophic (associated with moderate levels of suspended nutrients).[146] Alkalinity range is 90 to 200 mg/L CaCO₃.[147]

Diatoma bottnica may be 57 µm long and form attached zig-zag colonies in brackish water.[148]

Melosira

Melosira sp. [1]

Aulacoseira granulata © Barbara Meyer

Oreochromis niloticus prefer to prey on the large size diatoms, such as Melosira granulata (Aulacoseira granulata).[149] One single cell may be 22 to 37 µm long and 3.5 to 5 µm in diameter.[150] Melosira granulata is often found in turbid water.[151] Melosira sp. are meroplanktonic, meaning that they are part of plankton only during the larval stage of their life and spend their adult lives in between the plankton on the reef, which they may enter due to wind-induced mixing.[152] Though Melosira granulata may also thrive in waters with relatively little nutrients [153], Melosira are considered to have high-nutrient requirements and may occur in completely mixed shallow eutrophic waters. Melosira sp in general are characteristic for low salinity and low alkalinity waters.[154] Melosira granulata may thrive at 7 pH, 110 mg/L bicarbonate alkalinity and 260 mg/L hardness [155] / at 7 to 8 pH [156] / 7.2 to 8.5 pH (total bicarbonate alkalinity: 80 to 170 mg/L) [157] / 7.9 to 8.4 pH (Cl 64 mg/L ; NH³ 0.28 mg/L ; P 0.23 mg/L) [158] / at 8 to 9 pH.[159] Melosira granulata is associated with freshwater lakes [160], but Melosira granulata may also be considered euryhaline (may thrive in a wide range of salinities).[161][162] Melosira granulata is more abundant at higher temperatures. [163] Dominance of Melosira granulata requires high levels of silicon and high loadings of phosphorus and nutrient fluxes.[164] The alkalinity range may be 30 to 165 mg/L CaCO₃.[165] Melosira granulata is less seasonal than offshore populations of Melosira victoriae and Melosira nyassensis.[166]

Melosira / Aulacoseira (and cyclotella) species are Centrophycidae; centric diatoms as opposed to the other class: the pennate genera. The principal limiting resources of Melosira are light and phosphorus (and silica).[167] Melosira distans and Melosira ambigua need much light and have low phosphorus requirements and Melosira nyassensis needs the least light and the most phosphorus. Melosira granulata (which may adjust to light availability) and Melosira agassizii are intermediate.[168] Melosira italica v. valida develops optimally in running water (reophilous).[169] Melosira italica v. Italica is perennial and periphytic, associated with terrestrial habitats, but often suspended in the water.[170]

Navicula

Anomoeoneis sphaerophora © Glenodin

Navicula radiosa © DUS

Navicula species may be preferentially selected by Oreochromis niloticus.[171][172] Navicula radiosa (aka Schizonema radiosum) may be 40-120 μm long and 8-12 μm wide [173], or 52-105 µm long and 8.8-11.2 µm wide.[174] It thrives at 21 to 27°C. It is often found in littoral waters and is indifferent of pH (>7 pH) and cationity.[175] Navicula radiosa may thrive in water with pH fluctuating from ~7 to 9.5 pH. (total P > 48 µg/L; nitrate-nitrogen > 80 µg/L)[176] Navicula radiosa may attach to substrates, but not readily.[177]

Most other navicula are small. Navicula species are considered to be planktonic; floating suspended in the water.[178] Navicula radiosa var. radiosa is 38-45 µm long, may be periphytic, current indifferent and confined to freshwater.[179] Navicula placentula (30-50 μm long and 12-20 μm [180], or 23-28 µm long) may occur suspended in shallow waters.[181] Navicula gottlandica var. gottlandica (36-44 µm long, 8-10 µm wide) may thrive in freshwater and brackish water. The temperature tolerance range is 0°-25°C.[182] Navicula atomus, Navicula cari, Navicula cocconeiformis and Navicula graciloides may grow in shallow lakes with 40 ppt salinity.[183] Navicula placentula f. rostrata is 37 µm long and 13.5 µm wide.[184] Navicula arenaria may be 30-80 µm long [185] and tolerate 8 ppt to 45 ppt salinity.[186] Navicula halophila (aka Craticula halophila f. robusta, aka Navicula cuspidata var. halophila) may be 20-90 (140) µm long and 8-18 µm wide.[187] Navicula halophila may grow in lakes with > 10 ppt salinity.[188] Navicula cryptocephala var. veneta (14-18 µm long and 5 µm wide) may occur over a broad range of salt concentrations in running water with pH over 7. It is periphytic or suspended in the (eutrophic) water. Never dominant. Range of tolerance is 0-25°C.

Navicula cryptocephala (20-40 μm long [189], or 21-34 µm long, 5.2-6.5 µm wide[190]) may grow at 15 ppt salinity [191], needs pH over 7 and nitrogen in the form of ammonia or amino acids. It is eutrophic and common in both flowing and standing water. Navicula cryptocephala is perennial and may tolerate between 0 and 25°C.[192] It is favoured by high light penetration [193] and is considered eurytopic (the ability to exist in a wide range of chemical environments) and may thrive at 0.15 to 4.6 mg/L nitrate, 7 to 65 mg/L chloride, 0.13 to 0.59 mg/L total phosphorus (as PO₄^-) and 0.00 to 0.28 mg/L NH₃ [194], and in shallow water (<50 cm) at 1100 mg/L Na; 33 mg/L K; 8 mg/L Ca; 4 mg/L Mg; 3 mg/L SiO₂; 45 SO₄; 830 mg/L Cl and 26.5 meq/L alkalinity (carbonates plus bicarbonates).[195]

Anomoeoneis sphaerophora (aka Navicula sphaerophora) may be 40-80 μm long [196] or 25-200 µm long and 12-60 µm wide.[197] It is officially a benthic freshwater specie [198], but may be associated with Spirulina platensis dominance (and Nitzschia sigma) in highly alkaline, saline waters [199] (8.3 - 10.6 pH) [200]page280. Together with Nitzschia sp. 1 (12% of diatoms present) and Nitzschia sigma (8%) it may predominate (54%) in 18 ppt salinity, 284 mg/L potassium, 54 mg/L SiO₂, 554 meq/L alkalinity, 120 mg/L phosphates and 9.8 pH. Together with Nitzschia sp. 1 (35% of diatoms present) and Nitzschia sigma (13%) it may dominate (43%) in tropical 2 ppt salinity, 53 mg/L potassium, 10.6 mg/L calcium, 32 mg/L SiO₂, 70 meq/L alkalinity, 11.2 mg/L phosphates and 10.3 pH.[201]

Anomoeoneis sphaerophora var. sculpta or Navicula sphaerophora var. rostrata may dominate in <50 cm shallow waters at 9.6 pH and 25.5-130 meq/L (carbonates + bicarbonates) alkalinity (908-4810 mg/L Na; 22-45 mg/L K; 7-8 mg/L Ca; 1-6 mg/L Mg; 0.4 mg/l Fe; 0.7-3 SiO₂; 45-68 mg/L SO₄; 674-2680 mg/L Cl).[202] Anomoeoneis sphaerophora var. sphaerophora is benthic and may dominate in 13 to 64 cm shallow fresh and brackish waters at pH 9.7 to 10.1 and 23.1ºC to 34.2ºC ; conductivity > 2870 µS/cm, and may also thrive in waters with lower pH (5.0-10.4) and lower conductivity (318-12070 µS/cm), and at 23.0-36.1°C [203]

Nitzschia

Nitzschia sp. 1 [2]

Nitzschia accicularis © SERC

Nitzschia hungarica [3]

Nitzschia sigma © Frank Fox

Nitzschia hungarica [4]

Nitzschia sigmoidea [5]

Nitzschia vermicularis © A. Mikhaltsov

Pseudonitzschia pungens [6]

Pseudonitzschia pungens - multiple overlap [7]

Pseudonitzschia pungens - multiple overlap [8]

Oreochromis niloticus may prefer Spirulina and Nitzschia acicularis the most.[204] Nitzschia acicularis (aka synedra acicularis) may be 30-50 µm long.[205] / 30-100 µm long and 3-4 µm wide [206] or 30-150 µm long and 2,2-5 µm wide.[207] Cell volume may be 280 μm³.[208] / may vary from 248 μm³ to 800 μm³[209]. Nitzschia acicularis is solitary motile in brackish / freshwater.[210] Nitzschia acicularis may tolerate high salinity.[211] Alkalinity range is 80 to 220 mg/L CaCO₃.[212] Nitzschia acicularis may thrive in water with pH fluctuating from ~7 to 9.5 pH. (total P > 48 µg/L; nitrate-nitrogen > 80 µg/L)[213] Nitzschia acicularis may thrive in water with 8.3-8.6 pH, 4.5-7.0 DO, 125-309 total alkalinity, 70-220 mg/L Cl, 10-45 mg/L sulphate, 2-4 mg/L phosphate, 6.9-12.6 mg/L Mg, 7.5-10.5 mg/L Ca, 4.1-0.0 mg/L nitrate, 2.5-5.0 mg/L ammonium and 17-18.5ºC[214] Nitzschia acicularis may be found simultaneously in its planktonic and attached forms. Most intensive development of Nitzschia acicularis may primarily be in shallow waters in the river delta areas. It is typically found in rivers, ponds, and sometimes streams and bogs, but is very rarely found in lakes.[215]

Nitzschia are Pennatophycidae [216], which are epipelic diatoms; benthic (=not free floating) diatoms growing on sediment.[217] Upper ammonium tolerance of diatoms may be 3600 μM.[218] Nitzschia species are not dominant at temperatures below 23°C.[219] Many Nitzschia species stop growing at pH values of 8.7 to 9.1, and data suggest that smaller species have a higher upper pH limit for growth than larger species.[220] Most Nitzschia may survive in 10 pH.[221] Nitzschia are intermediates along the silicon:phosphorus gradient; with relatively balanced silicon and phosphorus requirements.[222] Nitzschia species do very poorly in low SiO₂ waters [[223]] and may be associated with Spirulina platensis blooms at 37-41 ppt salinity.[224] Nitzschia species produce more EPA at higher temperatures.[225]

Nitzschia sigma may be 388 µm long [226] 35-1000 µm long [227] / 30-200 µm long and 4-13 µm wide [228], or 40-180 µm long and 4-8 µm wide[229], is periphytic, thrives at pH >7, and may occur over a wide range of salt concentrations. [230] It is associated with fresh- [231], saline, alkaline [232], and even hypersaline waters.[233] It may tolerate up to 45 ppt salinity.[234] Nitzschia sigma is capable of free movement [235], benthic and typically found in estuarine (brackish) waters. It has its optimum at 25°C or higher.[236] It is tolerant of pollution. [237] Nitzschia sigma grows well when exposed to 380–450 μM water ammonium concentrations.[238]

• It may do well (7% of diatoms present) in 1.9 ppt salinity, 333 mg/L potassium, 4.1 mg/L calcium, 5.1 mg/L magnesium, 77 mg/L SiO₂, 79 meq/L alkalinity, 4.7 mg/L phosphates and 9.6 pH. (together with Nitzschia sp.3, in Cratar)
• Together with Nitzschia sp. 1 (12% of diatoms present) and Amonoeoneis sphaerophora (54%) it may grow well (8%) in 18 ppt salinity, 284 mg/L potassium, 54 mg/L SiO₂, 554 meq/L alkalinity, 120 mg/L phosphates and 9.8 pH.
• Together with Nitzschia sp. 1 (35% of diatoms present) and Amonoeoneis sphaerophora (43%) it may grow well (13%) in 2 ppt salinity, 53 mg/L potassium, 10.6 mg/L calcium, 22 mg/L magnesium, 32 mg/L SiO₂, 70 meq/L alkalinity, 11.2 mg/L phosphates and 10.3 pH.
• It may dominate (41% of diatoms present) in 3.8 ppt salinity, 284 mg/L potassium, 177 mg/L SiO₂, 107 meq/L alkalinity, 9.2 mg/L phosphates and at 9.4 pH.
• It may dominate (45% of diatoms present) in 1.9 ppt salinity, 54 mg/L potassium, 12 mg/L calcium, 44 mg/L magnesium, 28 mg/L SiO₂, 30 meq/L alkalinity, 5.2 mg/L phosphates and at 10.5 pH.
• It may dominate (48% of diatoms present) in 5.8 ppt salinity, 69 mg/L potassium, 5.7 mg/L calcium, 16 mg/L magnesium, 34 mg/L SiO₂, 163 meq/L alkalinity, 15.5 mg/L phosphates and at 10.5 pH.[239]

Nitzschia sp. 1 may attach to substrates [240] and concentrations occur when input water has high Si:P ratios (warm, wet climate).[241] Nitzschia sp. 1 may be 179 µm long and 6 µm wide.[242] Nitzschia sp. 1 (only 85 µm long) is benthonic and only dominant in extremely shallow (saline, alkaline) waters.[243] Similar to Amonoeoneis sphaerophora and Nitzschia sigma, it may do very well (35% of diatoms present) in 2 ppt salinity, 53 mg/L potassium, 10.6 mg/L calcium, 32 mg/L SiO₂,70 meq/L alkalinity, 11.2 mg/L phosphates and 10.3 pH. Equally so, it may also grow well (12% of diatoms present) in 18 ppt salinity, 284 mg/L potassium, 54 mg/L SiO₂, 554 meq/L alkalinity, 120 mg/L phosphates and 9.8 pH.[244]

Nitzschia hungarica (aka Tryblionella hungarica; 35-130 µm long [245]) is benthonic and only dominant in extremely shallow (saline, alkaline) tropical waters.[246] Nitzschia hungarica is motile, current indifferent, epilythic (growing on sediment), thrives in brackish (/ fresh[247]) and running water with pH >7.[248] It may do well (29% of diatoms present) in 3.7 ppt salinity, 174 mg/L potassium, 8.7 calcium, 1500 mg/L sulphates, 11.8 mg/L SiO₂, 87.4 meq/L alkalinity and 19 mg/L phosphates and 9.0 pH.[249] Variations in nutritional components in its medium may not considerably influence fatty acid profiles in Nitzschia hungarica.[250]

Nitzschia vermicularis may be motile in brackish waters and may be 220 µm long and 18 µm wide[251], 75-250 µm [252], 170 µm [253] or 140 µm long, and 6 µm wide. It is periphytic, pH indifferent, current indifferent, and thrives in fresh water, tolerating small amounts of salt. It is characteristic of the zone where oxidation of biodegradable compounds is complete.[254]

Nitzschia sigmoidea may attach to substrates [255], be motile, suspended in brackish water or freshwater and may be 314 µm [256] 90-500 µm [257] / 75-250 µm [258] / 282-350 µm long and 12,5-26 µm wide. It may be periphytic, eutrophic, current indifferent, alkaliphilous and characteristic of the zone where oxidation of biodegradable compounds is complete. It is perennial and tolerates 0 to 25°C.[259]

Nitzschia palea (aka Synedra palea; 12-42 µm long[260], or 15-70 µm long and 2,5-5 µm wide[261], or 19-53 µm long, 3.8-5 µm wide) may be the most resistant and most tolerant of all diatoms. It is solitary motile [262], eurytopic (indifferent of chemical conditions), euryhaline (indifferent of salinity) and eurythermic (indifferent of temperature) and grows in polluted water (but containing moderate dissolved oxygen) forming a brown surface layer on rocks of rapids, as well as in quiet water on shallow silt banks.[263] Nitzschia palea may occur in shallow waters [264] at 43 ppt salinity.[265] Domination is reed-associated. Nitzschia palea may dominate in <50 cm shallow waters at 9.6 pH and 25.5-130 meq/L (carbonates + bicarbonates) alkalinity (908-4810 mg/L Na; 22-45 mg/L K; 7-8 mg/L Ca; 1-6 mg/L Mg; 0.4 mg/l Fe; 0.7-3 SiO₂; 45-68 mg/L SO₄; 674-2680 mg/L Cl).[266] Nitzschia palea may dominate in 13 to 44 cm shallow fresh water at pH 7.0 to 8.5, and at 23 to 32°C (Optimum range: 22.8-29.5°C); conductivity 430- 2110 µS/cm.[267] Nitzschia palea has its maximum rate of photosynthesis at 33°C and is strongly inhibited at 40°C.[268] Nitzschia palea is considered eurytopic (the ability to exist in a wide range of chemical environments) and may thrive at 0.15 to 4.6 mg/L nitrate, 7 to 65 mg/L chloride, 0.13 to 0.59 mg/L total phosphorus (as PO₄^-) and 0.00 to 0.28 mg/L NH₃. [269] Nitzschia palea is eutrophic, pH indifferent, current indifferent and may be suspended in the water or attached to substrates.[270]

Nitzschia frustulum (18 µm long) is an estuarine, benthic diatom [271] that is solitary motile [272] and develops optimally in stagnant waters (limnophilous).[273] Nitzschia frustulum (aka Synedra minutissima / perpusilla / quadrangula) is both benthonic and associated with Spirulina platensis blooms (eg. Lake Tulusia[274][275]). Nitzschia frustulum is a nitrogen heterotroph and dense populations of Spirulina platensis release organic nitrogen. In the presence of Spirulina platensis (so that the diatom can enter the plankton), Nitzschia frustulum is the dominant diatom in saline lakes with alkalinity 80 > mEq/L, but also survives in freshwater.[276] Nitzschia frustulum may grow in waters with 3 to 100 ppt salinity.[277] It may be predominant in the range of 3.9 to 4.8 ppt salinity, 164-188 meq/L alkalinity and 10.1-10.4 pH, but only when SiO₂ levels are very low (below 8.5 mg/L)[278].This is probably because Nitzschia frustulum needs little silicon in comparison to other diatoms. Nitzschia frustulum var. frustulum (aka Synedra frustulum) may be 5-60 μm long and 2-4,5 μm wide.[279]

Nitzschia americana grows optimally at 26 ppt salinity.[280] Nitzschia archibaldii may thrive at 7.1 to 8.2 pH, 0 to 15 mg/L carbonates plus 110 to 170 mg/L bicarbonates alkalinity and 188 to 260 mg/L hardness.[281] It may be 23 µm long and grow in marine / brackish water. It is solitary motile.[282] Nitzschia bolivianais is epilithic; growing on rocks.[283] Nitzschia closterium exhibits optimum photosynthetic activity at 10 ppt [284], but it may tolerate salinity over 35‰ (ppt)[285], even up to 100 ppt.[286] Nitzschia denticulata and Nitzschia dissipata (solitary motile[287], 11.9-72 µm long[288]) in particular (and Nitzschia accicularis to a lesser extent) may thrive at 7.2 to 8.5 pH (total bicarbonate alkalinity: 80 to 170 mg/L).[289] Nitzschia dissipata is benthic and typically found in estuarine (brackish) waters. It has its optimum at 25°C or higher.[290] Nitzschia fonticola (10-55 µm long [291] or 18-31 µm long) is euryhaline and may thrive in 7 to 50 ppt.[292] Unlike most diatoms, Nitzschia fonticola is a nitrogen heterotroph (requiring organic nitrogen).[293] Nitzschia granulata may grow in shallow waters at 43 ppt salinity.[294] Nitzschia intermedia is solitary motile, thrives in brackish or freshwater and may be 80 µm [295] or 132 µm long and 7 µm wide.[296] Nltzschia linearis (related to Nitzschia palea) is truly rheobiontic (especially found in running water).[297], 34-228 µm long [298], 60-150 µm long and 4-6 µm wide[299], or 106-157 µm long and 5.4-6.5 µm wide, periphytic, eutrophic, and thrives in running freshwater (at 7 pH or above) but able to tolerate small amounts of salt (< 500 mg/L). Tolerates 0 to 30°C.[300] Nitzschia ovalis may grow at salinities from 5–40‰ (ppt).[301] Nitzschia vitrea may grow in 3 to 100 ppt salinity.[302]

Some (Pseudo)Nitzschia species produce domoic acid, a neurotoxin that may cause amnesic shellfish poisoning in humans. Pseudonitzschia is a marine genus. Pseudonitzschia characteristically overlap at > 1/3 of its length. The overlap of cells to form long chains is generally one of the key characteristics that can be used to distinguish living cells of Pseudonitzschia from Nitzschia.[303] Pseudonitzschia pungens [304], Pseudonitzschia pseudodelicatissima [305]) and particularly Pseudo-nitzschia species in high pH conditions [306], such as the cosmopolites Pseudo-nitzschiaseriata delicatissima and Pseudo-nitzschiaseriata pseudodelicatissima, but most notably the cosmopolites Pseudo-nitzschiaseriata australis and Pseudo-nitzschiaseriata multiseries [307] may produce domoic acid in the presence of light.[308] Pseudo-Nitzschia may tolerate up to 45 ppt salinity.[309]

Rhopalodia

Rhopalodia gibba © diatomloir.eu

Rhopalodia vermicularis © Jean Peynichou

Rhopalodia spp. are littoral diatoms, thriving in brackish waters.[310] Rhopalodia sp are epipelic algae; growing on sediment.[311] Rhopalodia is endemic to East Africa [312].

Despite their low abundance in pond water, both wild and pond-cultured Oreochromis niloticus preferentially selected Rhopalodia vermicularis.[313] Rhopalodia vermicularis may be 125 μm long and 14 μm wide. [314] and dominate in shallow waters.[315] Rhopalodia vermicularis thrives in moderately saline and moderately alkaline, shallow waters. [316]. Rhopalodia vermicularis grows in fresh to hyperalkaline lakes; 7 to 9.5 pH and 10 to 100 meq/L alkalinity (sodium bicarbonate or calcium- plus magnesium bicarbonate), at 21 to 27°C. [317]

Rhopalodia gibba (aka Navicula gibba) may be 22-300 μm long and 18-30 μm wide [318], 75-205 µm long and 8-11 µm wide.[319], grow at pH 10 and low alkalinity; 9.[320] Rhopalodia is epiphytic [321], periphytic, solitary, and usually occurs in high pH fresh- or brackish water.[322] Rhopalodia gibba may occur in alkaline freshwater (< 500 mg salt/L), is eutrophic and may tolerate heavy pollution with nitrogen in the form of amino acids or ammonia. It is both periphytic and suspended in water. It occurs in lakes, rivers and streams and is current indifferent.[323] Rhopalodia gibba may also grow in 20 to 50 ppt salinity.[324] Rhopalodia gibba thrives in shallow water, positively correlating with total phosphates.[325] Nitrogen limitation may favor Rhopalodia gibba relative to other diatoms, presumably due to the ability of their cyanobacterial endosymbionts to fix atmospheric nitrogen. As ambient nitrogen levels decrease, the number of endosymbionts increases, but only in the presence of sufficient phosphorus. [326] Together with Synedra ulna, it may grow in 1.2 ppt salinity, 10 mg/L potassium, 56.4 mg/L calcium, 21 mg/L SiO2, 5.7 meq/L alkalinity, 1.9 mg/L phosphates and 8.6 pH.[327]

Rhopalodia gibberula (aka Epithemia gibberula / Eunotia gibberula) may be 25-80 µm long and 7-14 µm wide [328]), may grow in marine and freshwater [329] and may dominate in hypersaline waters.[330] Rhopalodia gibberula may thrive in 3 to 50 ppt salinity.[331]

Rhopalodia gracilis may dominate in shallow waters.[332]

Synedra Ulna

Synedra ulna © diatomloir.eu

Oreochromis niloticus prefer to prey on the large size diatoms, such as Syndra ulna [333] (aka Fragilaria ulna). It may be 27-600 μm long and 3,5-9 μm wide.[334] Synedra ulna may be considered a benthic freshwater diatom that thrives in shallow estuarine environments close to freshwater sources. [335] Synedra ulna readily attaches to substrates by mucilage stalks or pads.[336] It may form a bushy, attached colony in brackish / freshwater [337], in shallow, saline, turbid water [338], or in shallow, oligotrophic lakes,[339]. Synedra ulna is benthic (rocks, stones, plants) and may also be suspended in the water. It prefers dirty, flowing water with high nitrate, and may be most abundant at 22 to 39°C (optimum 25°C). It may tolerate 5.7-9.0 pH (optimum 6.4-8.3 pH).[340](page 877) Synedra ulna is perennial, suspended in the water, current indifferent, able to tolerate small amounts of salt and develops optimally at ph >7. It is eutrophic, characteristic of the zone where oxidation of biodegradable compounds is complete, or oxidation is still occurring.[341] Synedra ulna may dominate in saline, alkaline waters.[342] Alkalinity range is 37 to 170 mg/L CaCO₃.[343] Synedra ulna may thrive in water with 7.0-8.6 pH, 1.0-7.0 DO, 125-550 total alkalinity, 70-247 mg/L Cl, 10-60 mg/L sulphate, 2-5.6 mg/L phosphate, 6.9-23.5 mg/L Mg, 7.5-27.5 mg/L Ca, 1.6-9.0 mg/L nitrate, 2.5-10.2 mg/L ammonium and 17-34.5ºC[344] Synedra ulna has high silicon and low phosphorus requirements.[345] Together with Rhopalodia gibba, it may grow in 1.2 ppt salinity, 10 mg/L potassium, 56.4 mg/L calcium, 21 mg/L SiO2, 5.7 meq/L alkalinity, 1.9 mg/L phosphates and 8.6 pH.[346]

Anabaena

Anabaena cylindrica © snkonsta

Anabaena sp. are large filamentous and neurotoxin-producing cyanobacteria (blue-green algae) that exist as plankton. Feeding mostly on Anabaena spiroides, Oreochromis niloticus (mean total weight: 31.5 g) may ingest 5.1% body mass equivalent (wet weight basis).[347] Ingestion rates are higher on Anabaena cylindrica than on Microcystis aeruginosa.[348] Anabaena flos-aquae is much better assimilated (83%) than green algae. Gross growth efficiency of fish fed Anabaena flos-aquae was 46% in comparison to fish fed Chlamydomonas (22%) and Ankistrodesmus falcatus; 24%.[349] Tilapia grow much better on Anabaena than on Clamydomonas (green algae) [350] Nile Tilapia fed ration equal 3% of the total fish body weight, containing 1.5% Anabaena had higher growth and were relatively protected against A. hyrophila infection.[351] Anabaena circinalis may cause off-flavor in fish flesh.[352] In competition experiments between Anabaeana and toxic Microcystis aeruginosa, dominancy is mainly determined by the initial biomass ratio.[353] Anabaena circinalis and Anabaena spiroides thrive in salinity less than 3 ppt.[354] Anabaena tortulosa is relatively tolerant of salinity up to 15 ppt.[355] Anabaena spp. (and Anabaenopsis) are common in alkaline saline lakes. [356] Salt tolerance in cyanobacteria is increased by nitrogenous compounds (inhibiting Na⁺ influx), but by nitrate more so than by ammonium or glutamine.[357]

Spirulina

Spirulina platensis [9]

Arthrospira platensis © UT-Austin

Spirulina platensis [10]

Arthrospira platensis [11]

Spirulina platensis [12]

Spirulina platensis [13]

Spirulina (Oscillatoria, Arthrospira) are blue-green algae/cyanobacteria and a rich source of protein and potassium.[358] Spirulina platensis contains 50 to 65% protein (10% is non-protein nitrogen)[359], but at high salinities, protein levels decrease. [360] It is high in vitamin B1 and B6 and it is 85 to 95% assimilated. It may contain up to 14% lipids (of dry mass). [361] Spirulina is readily digested by tilapia due to it's thin (50 nm) cell wals, and is an effective exchanger of O₂ and CO₂[362] Spirulina platensis growth is optimum below 10.5 pH.[363] Spirulina platensis is naturally found in tropical regions inhabiting alkaline lakes (pH 9.4 to 11 ; HCO₃ + CO₂ > 51 meq/L [364]) with high concentration of NaCl and bicarbonates [365], but specifically tolerant to high levels of NaHCO₃.[366] It may however adapt to very different habitats, including freshwater.[367] Optimum salinity may be between 13 and 51 ppt [368] or 20 and 70 ppt [369] (seawater salinity is 35 ppt), but Spirulina may be outcompeted (by Picocystis salinarium) at salinities over 57 ppt. [370] At lower salinities, Spirulina's multicellular cylindrical trichomes (in an open helix) are longer, and filament size positively correlates with biomass, soluble phosphorus, wind speed, condensation and temperature.[371] Under high light intensity, helical forms may tighten.[372] In the tropics, Spirulina dominance is associated with hydrological stability rather than water chemistry.[373] At pH > 10.3, Spirulina is outcompeted by picoplankton such as Synechococcus and Synechocystis.[374] In highly alkaline conditions (>50 meq/L CaCO₃ alkalinity), 9.8-10.3 pH, and at higher salt levels (2.5 to 30 g. salt / L; mostly carbonates and bicarbonates), Spirulina platensis becomes predominant (with Anabaenopsis, Oscillatoria, Synechocystis), or even the only significant organism (> 30 g. salt)[[375]]:

• Lake Dariba (large), Sudan (100% of biomass); 9.9 pH [376], 147 meq/L alkalinity [377], 10 ppt bicarbonates, 14 ppt total dissolved salts (NaHCO₃+NaCl), 100 ppm fluoride, 100 ppm silica.[378]
• Lake Aranguadi, Ethiopia (100%); 10.3 pH, 51-67 meq/L alkalinity [379], 5.1 ppt salinity [380], 1.5 ppt Na (67 meq/L) [381]
• Lake Bodou, Chad (82-100%); 10.2-10.4 pH, 32-55 ppt salinity [382] (40 ha [383], max. depth 2 m.[384])
• Lake Djikare, Chad (<93%); 9.7-10.2 pH, 146-217 meq/L alkalinity [385],
• Lake Tulusia, Tanzania (predominant); 10.1-10.4 pH, 189-287 meq/L alkalinity [386], 4.6 ppt Na, 437 mg/L P, [387], max. depth 13 m.[388]
• Lake Bogoria, Kenya (predominant); 9.8-10.3 pH, 480-800 meq/L alkalinity [389], 37-41 ppt salinity, 28.6°C [390], 1500 meq/L alkalinity (max. depth 10 m)[391].

Spirulina platensis aka Arthrospira fusiformis (small biomass) may be grown on human urine.[392] At pH 8.4, urea may be used as a source of nitrogen up to 1.5 g./L [393], the best growth temperature being 29°C [394] at an appropriate slowly increasing urea feeding rate.[395] Regarding phosphorus, maximum biomass production at high light intensity was observed at 250 mg/L K₂HPO₄.[396] The optimum nitrogen:phosphorus ratio is 7:1 at optimum light intensity.[397] (in human urine N/P = 8.7:1[398]) Spirulina is a thermophilic microorganism with an optimal growth temperature of 35 to 37°C.[399] The temperature range for optimum Spirulina growth is 30 to 35°C.[400] At 35°C there is a negative effect on biomass production but a positive effect on the production of protein, lipids and phenolics.[401] Spirulina may be cultivated in water with 16 g/L baking soda, 2 g/L Potassium nitrate, 1 g/L sea salt, 0.1 g/L potassium phosphate and 0.01 g/L iron sulphate. [402] In an open raceway system dissolved oxygen may reach 30 mg/L at 28°C. Above 25 mg/L Spirulina growth is inhibited.[403] During a period of nitrogen starvation, Spirulina platensis may survive and grow unaffected based on/due to prior storage of nitrogen in pigment proteins (C-Phycocyanin).[404] Spirulina biomass is not controlled by cyanophages. They rather occur in a more mutualistic relationship.[405][406][407]

Oreochromis niloticus may fairly tolerate salinity up to 10 ppt [408] Tilapia may tolerate 0.5% salinity (5 ppt).[409] At 8 g / L salinity adult Oreochromis niloticus may be stocked at 40 fish / m³. At 15 g/L salinity total production is more than halved.[410] Oreochromis niloticus may also (barely) survive in lakes with ~27‰ salinity.[411] Oreochromis niloticus need 7.4-8.2 pH; 50-140 mg CaCO₃ alkalinity and 140 mg CaCO₃/L hardness.[412]

Tilapia fed solely on raw Spirulina keep normal reproduction throughout three generations.[413] Larval tilapia that were fed solely raw Spirulina at a feeding rate of 30% (on a dry basis) of bodyweight in the first 3 weeks, 10% in weeks 4–6, and 3% in weeks 7–10, kept growing without any abnormality[414], at a slightly lower rate than fish fed fishmeal. Fish fed Spirulina had higher protein, polar lipid, linoleic acid and γ-linolenic acid contents and lower ash and omega-3 contents than fish fed the commercial diet.[415] Elastic modulus of flesh of the Spirulina-fed fish was significantly higher and viscosity lower.[416] In Tilapia aurea fed Spirulina platensis, food conversion was 2.0.[417] In Oreochromis mossambicus, Spurilina maxima may replace up to 40% of fish meal without negatively affecting growth.[418]

Larval Tilapia (Oreochromis niloticus < 3.4 cm) prefer consuming Spirulina platensis over Euglena gracilis (flagellate protists), and is also more readily assimilated. Tilapia prefer both species over Chlorella vulgaris (green algae, 45% dry matter protein), which is hardly ingested by larval tilapia.[419] Tilapia prefer Spirulina over Navicula (a diatom).[420] Dietary Spirulina incorporation increases antioxidant activity in tilapia.[421] When live Spirulina partly replaces commercial feed, fish mortality due to Aeromonas hydrophila infection decreases with an increase in the Spirulina level in the diet.[422]

An algal raceway may contain 6 to 30 cm water; 600.000 L / 2 ha. In most algal cultivation systems, light only penetrates the top 3 to 4 inches (7.5 cm to 10 cm). In 15 to 30 cm deep water, yield may be 55.000 to 110.000 kg / ha / year. When algae growth is 6 to 7 cm thick, yield may be 140.000 kg / ha / year. (DO influx is 10 mg/L, efflux is 23 mg/L) 10.000 kg fish need 106.000 kg algae / year.

Microcystis

In lakes where Microcystis spp. are the most abundant, Microcystis sp. may account for more than 80% of ingested phytoplankton.[423] Various cyanobacteria may produce toxins (eg Microcystis aeruginosa). Average digestion rate of Microcystis aeruginosa (cyanobacteria producing neurotoxins and hepatotoxins) by Tilapia fingerlings is 58 to 78% at 25℃.[424] In Oreochromis niloticus a high rate of defaecation of undigested Microcystis may occur.[425]

Microcystis aeruginosa may survive in a wide range of salinities.[426] Oreochromis mossambicus exposed to extracts from Microcystis aeruginosa showed significant plasma hypocalcaemia.[427] Chronic exposure to toxin producing cyanobacteria (Microcystis aeruginosa) may not (115 days trial[428], 90 days trial[429]) negatively affect growth, feed conversion efficiency, health or mortality in Oreochromis niloticus. Microcystins do accumulate in muscle tissue (and particularly in the liver), which may exceed the upper limit of the tolerable daily intake of microcystins suggested by the WHO (0.04 μg/kg body weight/d).[430] The strong tolerance microcystins may be due to a phase II detoxification enzyme.[431] Accumulation of microcystis increases lipoxidation (a biomarker of oxygen-mediated toxicity) in the liver.[432] Microcystin concentrations in the liver and intestine may gradually decrease as a result of the capacity in Tilapia to depurate and excrete microcystins into the bile and surrounding water, to avoid toxicity.[433] During the depuration period, muscle tissue may contain the highest concentration of microcystins, which may exceed the tolerable limit for humans (even in combined diets).[434] Microcystis wesenbergii is non-toxic, less competitive, but more suited to low phosphorus environments than Microcystis aeruginosa.[435] Microcystis flos-aquae is more dominant in salinity above 3 ppt, whereas Microcystis aeruginosa is dominant in salinity up to 3 ppt.[436]

Periphyton

Periphyton is a mixture of algae, cyanobacteria, heterotrophic microbes and detritus (mainly scraps of macrophytes and mud [437]) attached to submerged surfaces embedded in a slimy mucopolysaccharide matrix.[438] Oreochromis niloticus graze actively, with little selectivity, on the periphyton established on artificial substrates in cages. Both animal and plant material are removed to an equal extent, but less smaller particles are ingested.[439] Surface-grazing on periphyton is greater than on Microcystis aeruginosa. For tilapia, filter-feeding may be a relatively unimportant method of ingesting algae.[440] Tilapia mossambica feeds almost exclusively on periphytic detrital aggregate. (Assimilation efficiencies: organic matter 63%, protein 77%, carbohydrate 63%) [441] Feed conversion ratio of dry matter periphyton may be 2.81. Fish growth may be sustained on periphyton despite 55% (dry matter) ash content.[442] The fresh microbial mat was 81% digestible by Nile tilapia, comparing favorably with commercial catfish feed in digestibility by Nile tilapia. The dried form was significantly less digestible.[443] Tilapia are equipped with a 'stomach bypass' to be able to bypass or regurgitate unwanted materials.[444]

Algae meal

Under most unnatural feeding conditions tilapia are unable to sufficiently ingest high volumes of algae. They may need constant grazing to fulfill their nutrient requirements.[445] Tilapia (Sarotherodon niloticus) grow better on fishmeal (fish meal may contain 74% protein and 8% lipids.[446]) than on a 25% protein green algae meal (Cladophora glomerata). Weight gain decreased as the level of algal protein increased as replacement of fish meal. Protein digestibility was highest on a 5:1 ratio (fishmeal : green algae meal).[447] Protein synthesis (with normal sulfur and carbon content) by green algae during the night may match protein synthesis during the day (in Dunaliella tertiolecta).[448] Protein derived from algae does not promote adequate growth in Rainbow trout.[449] Fish fed 5% ulva meal (Green algae; Ulva rigida) showed increased growth, feed conversion ratio and protein efficiency ratio.[450] Ulva meal may replace soy bean meal to the extent of 20% without negatively affecting growth of male larval tilapia. Feed conversion ratio increased with increasing ulva meal content.[451] Green algae meal (Hydrodictyon reticulatum) may replace meal to the extent of 25% without negatively affecting growth of Oreochromis niloticus and Tilapia zillii fingerlings.[452] Spirulina maxima meal protein can replace up to 40% of the fish meal protein in Oreochromis mossambicus fry diets without negatively affecting growth.[453]

Off-flavor

Cyanobacteria causing off-flavor (by geosmin and 2-methylisoborneol, MIB in fish flesh) are Oscillatoria tenuis, Anabaena circinalis and Pseudanabaena catenata. Tilapia flesh derived from cage culture provided a lower possibility of off-flavor contamination than those from earthen ponds.[454] Geosmin (1,10-trans-dimethyl-trans-9-decaol) in fresh tilapia at concentrations ranging from 7.55 to 9.85 μg/kg of fish flesh is detected as 'muddy flavor' by sensory evaluation. In brackish fish, only geosmin levels below 2.6 μg/kg remain undetected. The highest geosmin concentrations are contained in the intestines, followed by abdominal, skin and muscle tissues, subsequently. It takes at least 16 days in static clean water to eliminate the muddy flavor from geosmin absorbed through the skin.[455]