Comparative study on growth, digestive function and intestinal microbial composition of female Chinese mitten crab Eriocheir sinensis selected at different growth stages in rice-crab culture systems

Abstract

This study sought to characterize the growth/development and digestive function of female Chinese mitten crabs (Eriocheir sinensis) under a rice-crab symbiotic co-culture model. Feeding experiments were conducted at the Langu Agricultural Cooperative in Gongzhuling City, Jilin Province. The samples were randomly collected on July 15 (T0 stage), July 30 (T1 stage), August 15 (T2 stage), August 30 (T3 stage), and September 15 (T4 stage). A total of 90 female E. sinensis were randomly collected at each time point (i.e., 30 from each of the three rice fields as three replicates between stages). Our findings indicated that the weight of the female E. sinensis increased from 33.89 ± 1.52 g to 88.32 ± 4.62 g within two months. Weight gain rate (WGR), specific growth rate (SGR) and weight gain (WG) increased first and then decreased, WGR and SGR reached their peak at the T2 stage, and the maximum WG occurred at the T3 stage. The gonads began to develop in the T2 stage, and the gonadosomatic index (GSI) increased significantly from the T2 to the T4 stages. The intestinal trypsin and amylase activity and the mRNA expression levels of the digestion-related genes CTRB1, PRS44, TGL, and ESPT reached their maximum in the T2 stage but decreased thereafter. Trypsin and lipase activity in the hepatopancreas exhibited a downward trend from stages T0 to T4; however, amylase activity and the mRNA expression levels of the PRS44 and TGL genes increased first and then decreased. The intestinal diameter, villus height, and villus width of the female E. sinensis increased with development stage, with the T2, T3, and T4 stages exhibiting significantly higher values than the T0 stage (P < 0.05). The intestinal flora structure of the female E. sinensis also changed with development stage. At the phylum level, the intestinal microbiota was mainly represented by Tenericutes, Proteobacteria, Firmicutes, and Bacteroidetes. In conclusion, the female E. sinensis raised in the rice fields reached a rapid growth period from July 30 to August 30 under the experimental conditions described herein. Moreover, the proposed culture conditions promoted gonad and intestinal development, digestive function, and nutrient absorption.