Potential of algae as aquaculture feed ingredient

Algae are simple plants that can range from the microscopic microalgae to large seaweeds, macroalgae microalgae include green, red, and blue-green algae or cyanobacteria. Algae are already exploited abroad as shrimp and poultry feed and as health food. In this Philippines, however, they are already utilized as food or animal feed. To maximize their utilization and exploit their presence in inland water resources such as ponds and rice paddies, different species of algae were collected from PhilRice, Nueva Ecija Atrium, Greenhouse (GH), Screenhouse 1 (SH1), Screenhouse 2 (SH2); Pangasinan, Pangasinan 1 (PS1F) and Pangasinan 2 (PS2S); Brgy. [village] 20 Ilocos Norte (INB20); and Mindanao (MD). Their morphology, identity, and physicochemical and nutritional properties were determined. The jelly-like SH1, INB20, PS2S, and MD were identified as Nostoc Commune Voucher and Aphanothece pallida (Kutzing) Rabenhorst, respectively. The fibrous algae Atrium, GH, SH2, and PS1F were identified as Oedogonium, Rhizoclonium, and Spirogyra, respectively. Selection of the best algal sample for feed ingredient formulation was initially based on protein content. PS1F and PS2S, having high crude protein (27.43 and 23.61%, respectively) were chosen and subjected to cytotoxicity test and lethal concentration measurement. The gelatinous algae, PS2S was selected as feed ingredient due to its high crude protein (23.61%), known level of toxicity (251.19 ppm), and sample availability for feed testing. However, the feed ingredient formulated had low fish acceptability due to its gel-like structure resulting in very low percentage of fish survival. Interestingly, the use of fibrous algae, SH2 gave significantly higher percentage of growth (38.85%) and survival (91.67%) of Nile tilapia at 25:75 algae and commercial feed ratio. This work has therefore shown the feasibility of mixing algae in aquaculture feeds, however, a follow up study is recommended to establish the economic viability of manufacturing algal incorporated animal feed.