Optimal dietary lipid and protein level for growth and survival of catfish Clarias magur larvae

Abstract

Large scale farming of Clarias magur (Indian walking catfish) is limited due to the non-availability of seed because of high mortality rate occurring during its larval rearing. The aim of the present study was to develop an optimal strategy based on the dietary lipids and proteins for enhancing the larval survival. A 3-week study from 14-35 day post hatching (dph) was conducted to elucidate the effects of dietary lipid and protein level on growth, survival and mRNA expression of growth related genes of C. magur larvae. Significantly (P < 0.05) high growth on average wet weight basis and survival rate was observed in 8% dietary lipid inclusion level followed by 10% and 12% lipid contents from 14-35 dph larval rearing phase. The effect of dietary lipid on the body composition was also reflected on the lipid content of larvae where a significant difference was observed. Similarly, growth-related genes like growth hormone (GH) and insulin-like growth factor I (IGF-I) exhibited a significantly high expression at 8% lipid level compared to 10% and 12% whereas, insulin-like growth factor binding protein3 (IGFBP3) showed a reverse trend. Based on the results, 8% dietary lipid along with the protein combination improved the performances significantly with regard to growth and survival. However, this experiment did not help to differentiate whether the differences observed at different time points are due to dietary protein level or the age of larvae. Hence, another experiment was conducted in which diets were formulated to contain different protein levels (55, 50 and 45%) with a constant 8% level of lipid in all the treatments along with commercial diet as control. The inclusion of 8% lipid and 55% protein was observed to show excellent performance with respect to growth, survival and the mRNA expression of important growth-related genes. Hence, a formulated diet with crude protein of 55% and 8% lipid can be suggested as the optimal microdiet for the larval rearing of C. magur.