Differential gut growth, gene expression and digestive enzyme activities in young grass carp (Ctenopharyngodon idella) fed with plant and animal diets.

摘要

Young grass carp (mean total length and weight, 5.5 cm and 1.8 g respectively) at the food transition stage from zooplankton or benthos to aquatic macrophytes, were fed with either duckweed or chironomid larvae for 60 days. Fish fed with duckweed had significantly higher gut growth than those fed with chironomid larvae in terms of length or weight. Consistent with this, the mRNA expression of epidermal growth factor (Egf) was higher in fish fed with duckweed than those fed with chironomid larvae, whereas the Igf II mRNA level of fish fed with duckweed was significantly lower than those fed with chironomid larvae. Consistent with higher appetite of fish fed with plant diets, the mRNA levels of neuropeptide Y (Npy), neuropeptide Y receptor Y8a (Npy Y8a), neuropeptide Y receptor Y8b (Npy Y8b) and leptin receptor (Ob-r) in fish fed with duckweed were simultaneously higher than those fed with chironomid larvae, and leptin receptor gene related protein (Ob-rgrp) expression was lower. The differential expressions might potentially contribute to gut growth of young grass carp fed with duckweed and adapted to herbivory. The mRNA levels of trypsin and amylase in fish fed with duckweed were significantly higher than those fed with chironomid larvae, and lipoprotein lipase expression was significantly lower. Concordant changes in enzyme activities of trypsin and lipase were observed. Our results suggested that in young grass carp, plant food not only stimulated gut growth possibly through Egf, but also up-regulated expressions of Npy, Npy Y8a, Npy Y8b and Ob-r as well as trypsin and amylase to increase the intake and digestion of plant food.