Partial or total replacement of soybean meal by cottonseed meal in practical diets for chinese mitten crab, Eriocheir sinensis: Effects on oxygen consumption, ammonia excretion, O:N ratio and amino transferases activities

This study investigate the effect of replacement of soybean meal (SBM) by cottonseed meal (CSM) on oxygen consumption, ammonia nitrogen excretion, O:N ratio and aspartate aminotransferase (ASAT) and alanine aminotransferase (ALAT) activities for Eriocheir sinensis. Seven isocaloric and isonitrogenous diets were tested with five replicates. CSM replaced 0, 33, 66 and 100% of SBM in four diets (CSM0, CSM33, CSM66 and CSM100) and lysine was added to other three diets (CSM33+lys, CSM66+lys and CSM100+lys). Oxygen consumption rates of crab fed CSM66+lys and CSM100+lys were significantly lower than crab fed CSM0, and crab fed CSM100+lys was significantly lower than crab fed CSM33 and CSM66. The ammonia excretion of crab in the CSM0 was significantly higher than that in all other treatments. Crab fed CSM33+lys, CSM66+lys and CSM100+lys discharged less ammonia than crab fed CSM33, CSM66 and CSM100. The O:N ratio indicated that protein was decreasingly used as an energy substrate when SBM was replaced by CSM. With lysine supplementation, the crab made use of lipid and carbohydrates as the most important sources of energy metabolism. Activities of ASAT in CSM66+lys and CSM100+lys were significantly lower than that in CSM0, CSM33 and CSM100. Results suggest that 100% of SBM can be replaced by CSM with lysine supplement in crab without affecting growth performance and with decreasing level of ammonia released into the water.