Effects of organic acids on growth and phosphorus utilization in rainbow trout, Oncorhynchus mykiss

The present study aimed to investigate the effect of phosphorus and various organic acids supplementation on growth, nutrient retention and loading in rainbow trout fed on low fishmeal based diets. Five experimental diets were formulated, Diet D1 (0.5P) was positive control with 0.5% inorganic phosphorus addition and D2 (OP, negative control) without addition of inorganic phosphorus. D3, D4 and D5 were supplemented with 1% fumaric (FuA), formic (FoA) and acetic (AA) acids, respectively. All the diets were fed until satiation to duplicate groups of 25 fish for 12 weeks. Feed conversion ratio (FCR) was recorded best with FoA diet and absorption of phosphorus was significantly higher (P < 0.05) in all the diets supplemented with organic acids and was similar to positive control. The phosphorus and nitrogen retention with FoA diet was significantly high (P < 0.05) as compared to OP diet, in turn reducing their excretion. Hence, the present study demonstrated that, without additional phosphorus in the low fish meal-based diets, FoA supplement improved growth performance, absorption and retention of phosphorus and nitrogen and reducing excretion; thus it can be better incorporated to develop environment-friendly feed for rainbow trout.