Armando GARCÃÆÃÂA-ORTEGA, Laura MARTÃÆÃÂNEZ-STEELE, Dennis GONSALVES, Marisa M. WALL, Paul J. SARNOSKI
Algal by-product meals from the Hawaiian biofuels industry were evaluated as ingredients in diets for juveniles of Nile tilapia (Oreochromis niloticus). Four experimental diets were formulated to fulfill fish nutritional requirements. The diets were made with fish meal, soybean meal, whole diatom (Nanofrustulum sp.) meal, or defatted green algae (Desmochloris sp.) meal as the test ingredients. A feeding experiment with juvenile tilapia of 2.6 ±0.1 g initial weight was carried out in a freshwater recirculation system with each diet treatment tested in triplicate tanks. Fish were fed the experimental diets to apparent satiation twice a day for 12 weeks and fish weight was measured every three weeks. Water temperature was maintained at 22.7 ±0.8 °C, salinity at 0.1 ±0.0 ppt and dissolved oxygen at 5.6 ±0.5 mg/L. At the end of the experiment a significant effect (P<0.05) of diet treatments was found in fish growth and feed utilization, with specific growth rate, food conversion ratio, and retained nitrogen efficiency being highest for the green algae-based diet. Lipid content in the diets was lower than expected for the algae diets. Proximate composition analysis showed no significant difference (P>0.05) in the protein content of the fish bodies among the diets. Results indicate the suitability of the green algae byproduct meal as an ingredient in Nile tilapia diets. Diatom meal also showed interesting potential for use as an ingredient in tilapia feeds.
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