Effects of Three Compound Attractants in Plant Protein Diets on Growth, Immunity, and Intestinal Morphology of Yellow River Carp Cyprinus carpio var

Abstract

A feeding experiment was conducted to evaluate the effects of three compound attractants on the growth performance, immunity, and intestinal morphology of Yellow River (YR) carp. Five treatment groups were included in the feeding experiment. Group I consisted of a fishmeal-based diet (positive control), and group II was a plant protein diet (negative control). The compound attractants 1 ( $0.06\%\text{dimethyl}-\text{beta}-\text{propiothetin}\left(\text{DMPT}\right)+0.22\%\text{tangerine}\text{peel}\text{powder}+0.75\%\text{yeast}\text{powder}$ ), 2 ( $0.05\%\text{garlic}\text{powder}+0.06\%\text{DMPT}+0.75\%\text{yeast}\text{powder}$ ), and 3 ( $0.07\%\text{sodium}\text{glutamate}+0.22\%\text{tangerine}\text{peel}\text{powder}+0.34\%\text{betaine}$ ) were added to the plant protein diet, belonging to groups III, IV, and V, respectively. The three different compound attractants significantly improved the weight gain rate, special growth rate, and protein efficiency ratio of Yellow River (YR) carp ( $P<0.05$ ) compared with the negative control, among which group III performed best. Similarly, group III had significantly higher serum lysozyme (LZM) and acid phosphatase (ACP) activities than the negative control, and groups III, IV, and V depicted significantly higher LZM activities in the liver and gill ( $P<0.05$ ). Groups III, IV, and V revealed significantly higher superoxide dismutase (SOD), catalase (CAT), and total antioxidant capacity (T-AOC) activities in the serum and liver than the negative control ( $P<0.05$ ), while the malondialdehyde (MDA) content was the opposite ( $P<0.05$ ). Moreover, the height and width of the plica in the foregut and midgut and the thickness of the midgut muscle layer in group III were significantly higher than those in the negative control ( $P<0.05$ ). Therefore, adding compound attractants in a plant protein diet can significantly enhance the total antioxidant and immune capacity, along with improved growth performance of YR carp. Similarly, compound attractants significantly elevated the height and width of the intestinal fold within the anterior and middle sections of the intestine, depicting that compound attractants promote intestinal digestion and absorption, thereby reducing intestinal injury. The results from the three experimental groups found that the compound attractants combined with 0.06% DMPT, 0.22% tangerine peel powder, and 0.75% yeast powder were more suitable for the basic plant protein diet of YR carp.