A lgal meals from Arthrospira platensis (Spirulina) and Schizochytrium limacinum were used to completely replace fish meal (FM) , fish oil (FO) and soy protein concentrate (SPC) in feeds for juvenile hybrid tilapia (Orechromis niloticus x O. mossambicus). Five isonitrogenous and isoenergetic feeds were formulated to replace fish and soy ingredients at 0%, 25%, 50%, 75% and 100% by algal meals (ALG) . Feeds were supplemented with lysine and methionine at increasing levels of ALG inclusion to meet the essential amino acids requirements of fish. Taurine was also supplemented in all feeds. A feeding trial was performed in fish with an initial weight of 0.9 ± 0.1 g. Each feed treatment was tested in triplicate 90 L tanks in a water recirculation system at a density of fish 15 per tank. Feeds were manually fed to fish twice per day at 8 am and 2 pm for nine weeks. Water quality parameters during the trial were: temperature: 28.3 ± 0.2°C, salinity 0.1 ± 0.0 ppt, dissolved oxygen 6.5 ± 0.1 mg/L, pH 6.7 ± 0.3 and total ammonia nitrogen 0.0 ± 0.0 mg/L. At the end of trial data on fish weight gain, feed utilization and nutrient retention among treatments were evaluated with ANOVA and regression analyses.
Fish f eed intake was significantly higher (P<0.05) with increasing algal meals content in feeds, the highest found in treatments ALG 50, ALG 75 and ALG 100. The FM, FO, SPC-based feed (ALG 0) produced significantly lower growth (P<0.05) than all the feeds containing ALG, including ALG 100. Fish g rowth w as the highest in feeding treatments ALG 75 and ALG 50. A quadratic regression analysis to study t he relationship between fish weight gain and increasing replacement of FM, FO and SPC by algal meals indicated that maximum fish weight gain can be achieved at 70% replacement level. No significant differences (P>0.05) were found in FCR or feed efficiency among diets. However, nitrogen retention in fish was significantly higher (P<0.05) with ALG 50 and ALG 75, followed by ALG 100. No significant differences were found in final body proximate composition, with the exception of ash content. It's concluded that a feed made with 100% A. platensis and S. limacinum as the sole sources of protein and lipid produce higher growth and feed utilization in hybrid tilapia juveniles than conventional fish feed ingredients , confirming the quality and suitability of these algal in feeds for omnivorous farmed fish.