Algae for Tilapia
Tilapia (Oreochromis niloticus) may effectively control algal blooms in eutrophic waters.[1] 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.[2]
Tilapia feed selectively on large algae, mainly cyanobacteria and diatoms.[3] Nile tilapia is particularly effective in filtering the larger particle size taxa.[4] 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).[5] Surface-grazing on periphyton (mixture of algae, cyanobacteria, heterotrophic microbes and detritus attached to submerged surfaces) is also greater than on Microcystis aeruginosa. For tilapia, filter-feeding may be a relatively unimportant method of ingesting algae.[6]
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.[7] Dietary Spirulina incorporation increases antioxidant activity in tilapia.[8]
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.[9] 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).[10] Protein synthesis (with normal sulfur and carbon content) by green algae during the night may match protein synthesis during the day (in Dunaliella tertiolecta).[11] Protein derived from algae does not promote adequate growth in Rainbow trout.[12] Green algae ulva meal 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.[13]
