Algae for Tilapia

Tilapia start feeding shortly before dawn and feed continually until about dusk. They do not feed during the night.[1] Tilapia (Oreochromis niloticus) may effectively control algal blooms in eutrophic waters.[2] Blue-green algae 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.[3]

Dietary Spirulina incorporation increases antioxidant activity in tilapia.[4]

Selective feeding

Tilapia feed selectively on large algae, mainly cyanobacteria and diatoms.[5] Nile tilapia is particularly effective in filtering the larger particle size taxa.[6] Larger phytoplankton are being filtered proportionally more than the smaller phytoplankton, and cyanobacteria more than green algae (Scenedesmus, Ankistrodesmus, Tetraedron).[7] Ingestion rates are higher on Anabaena cylindrica (larger filamentous cyanobacteria that exists as plankton) than on Microcystis aeruginosa (freshwater cyanobacteria that produce neurotoxins and hepatotoxins).[8] Larval Tilapia (Oreochromis niloticus < 3.4 cm) prefer consuming Spirulina platensis (cyanobacteria) 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.[9] In Tilapia aurea fed the blue-green alga Spirulina platensis, food conversion was 2.0.[10]

Periphyton

Surface-grazing on periphyton (a slimy matrix/mixture of algae, cyanobacteria, heterotrophic microbes and detritus attached to submerged surfaces) is greater than on Microcystis aeruginosa. For tilapia, filter-feeding may be a relatively unimportant method of ingesting algae.[11] Tilapia mossambica feeds almost exclusively on periphytic detrital aggregate. (Assimilation efficiencies: organic matter 63%, protein 77%, carbohydrate 63%) [12] 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.[13] Tilpia are equiped with a 'stomach bypass' to be able to bypass or regurgitate unwanted materials.[14]

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.[15] Tilapia (Sarotherodon niloticus) grow better on fishmeal 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).[16] Protein synthesis (with normal sulfur and carbon content) by green algae during the night may match protein synthesis during the day (in Dunaliella tertiolecta).[17] Protein derived from algae does not promote adequate growth in Rainbow trout.[18] Green algae ulva meal (Ulva rigida) may replace soy bean meal to the extend of 20% without negatively affecting growth of male larval tilapia. Feed conversion ratio increased with increasing ulva meal content.[19] Green algae meal (Hydrodictyon reticulatum) may replace meal to the extend of 25% without negatively affecting growth of Oreochromis niloticus and Tilapia zillii fingerlings.[20] Spirulina maxima meal protein can replace up to 40% of the fish meal protein in Oreochromis mossambicus fry diets without negatively affecting growth.[21]