Performance and sensory evaluation of silver perch (Bidyanus bidyanus Mitchell) fed soybean or meat meal-based diets in earthen ponds

The performance of silver perch fed a commercially available diet based on meat meal (38%), grain legumes (18%), oilseeds (10%), wheat millrun (20%), fishmeal (5%) and fish oil (3%) was compared with experimental diets based on alternative protein sources in two experiments. In Experiment 1, two experimental diets contained similar contents of fishmeal and fish oil as the commercially available reference diet, but soybean (25%) and wheat millrun (> 31%) were used to reduce animal protein meals by approximately 50%. The digestible protein and digestible energy of the two experimental diets was either slightly lower (31.5% and 12.8 MJ kg(-1)) or slightly higher (34.9% and 14.3 MJ kg(-1)) than the reference diet (32.1% and 13.2 MJ kg(-1)). In Experiment 2, the two experimental diets contained no fishmeal but included higher amounts of rendered animal meals (41-48%). One of the diets had similar digestible protein to the reference diet (32%) while the other had only 25% digestible protein. Silver perch (38 g for Experiment 1 and 59 g for Experiment 2) were stocked into each of nine 0.1 ha earthen ponds with fish in three ponds fed each diet for 191 days (Experiment 1) or 187 days (Experiment 2). Survival was > 94% in all ponds in both experiments. In Experiment 1, growth rates and feed conversion ratios (FCRs) ranged from 2.1 to 2.4 g fish(-1) day(-1) and 1.7 to 1.9 respectively. Growth rates were significantly (P < 0.05) lower for fish fed the experimental diet with the lowest digestible energy content. Growth rates for fish fed the other experimental diet and the reference diet were similar (P > 0.05). In Experiment 2, growth rates and FCRs ranged from 2.3 to 2.4 g fish(-1) day(-1) and 1.6 to 1.7. There were no significant differences in fish performance indices for any of the three diets although experimental power was low (power=0.31). A blind consumer sensory evaluation (taste panel) of fish fed the three diets in Experiment 2 rated fish as 'highly acceptable'. The diet with the lowest digestible protein content produced the best fish in terms of 'smell liking', 'flavour liking', 'muddy flavour strength' and 'fresh flavour strength'. These results confirm that soybean meal and/or rendered animal protein ingredients including meat meal and poultry offal meal, and wheat can form the basis for high-performance, low-cost diets for intensive pond culture of silver perch.