Effects of dietary protein levels on growth performance, carcass composition, nutrient digestibility and digestive enzyme activity of the critically endangered peninsular carp, Hypselobarbus pulchellus (Day, 1870) fingerlings

The dietary protein requirement of the peninsular carp, Hypselobarbus pulchellus was investigated through a feeding trial conducted in aerated plastic tanks (50 L) with five isocaloric diets formulated to contain crude protein levels ranging from 20 to 40% (CP20, CP25, CP30, CP35 and CP40) using pure ingredients with casein and gelatin as the protein sources. Fingerlings (mean wt. 4.71 g) of H. pulchellus were fed at 5% of the biomass for a period of 60 days. The growth parameters increased with dietary protein level up to 35% followed by a decrease with CP40 diet. Lowest (p < 0.05) food conversion ratio was recorded with 35% protein diet. Protein efficiency ratio values were inversely proportional to the dietary protein level. The condition factor ranged from 0.94 to1.07 with no difference among the treatments. No difference (p > 0.05) was recorded in fish survival. Proximate composition analysis of fish carcass indicated no difference (p > 0.05) in moisture, fat and ash contents. Crude protein content on the other hand, showed values increasing with dietary protein level up to 35%, beyond which (CP40), it stagnated. Apparent digestibility coefficient for protein also increased gradually with the dietary protein level with a peak under CP35 and then decreased at CP40. Fat digestibility values, on the other hand, were similar (p > 0.05) for all diets. Analysis of the activity of digestive enzymes indicated highest activity of trypsin and total protease in both intestine and hepatopancreas of fish fed 35% crude protein diet. The second- order polynomial regression analysis for weight gain rate and specific growth rate indicated a dietary protein requirement between 31.80 and 32.76% for the fingerlings of H. pulchellus. This information on protein requirement would be useful in developing species specific feed for this critically endangered peninsular carp.