Effects of stocking density on the growth performance, physiological response and intestinal microbiota of juvenile Echiura worms ( Urechis unicinctus )

Abstract

Aquaculture of the Echiura worm Urechis unicinctus has developed rapidly in recent years. However, the artificial cultivation technology remains to be perfected. In this study, the effects of stocking density on the growth performance, physiological responses and intestinal microbiota of U. unicinctus juveniles were evaluated. Juvenile worms were randomly stocked at densities of 200 U (U. unicinctus/m3), 500 U, 1,000 U and 2,000 U, in aquariums. The results indicated that the contents of triglycerides, glucose, total cholesterol, lactic acid, alkaline phosphatase, acid phosphatase and aspartate transaminase in the coelomic fluid of U. unicinctus juveniles were significantly enhanced with increasing stocking density. The digestive enzyme activities increased with increasing stocking density from 200 U to 1,000 U, before exhibiting a significant decrease in the 2,000 U group. In contrast, the antioxidant capacity of U. unicinctus juveniles was suppressed under high stocking density conditions. In case of the intestinal microbiota of U. unicinctus juveniles, Actinobacteria were more abundant in the 200 U group; SJA15, Gluconobacter and OP81 were higher in the 1,000 U group; Burkholderiales and Limnohabitans were enriched in the 2,000 U group. The highest and lowest survival rates of the U. unicinctus juveniles were recorded in the 500 U and 200 U groups respectively, and high stocking densities negatively affected the individual growth performance. In summary, due to the highest survival rate and appropriate growth performance and physiological responses, 500 U was considered to be the optimal stocking density for the cultivation of U. unicinctus juveniles.

Effects of Salinity on the Growth, Physiological Characteristics, and Intestinal Microbiota of the Echiura Worm (Urechis unicinctus)

“…The trend was similar with the previous feeding trial report of U. unicinctus juveniles with different salinities (Zheng et al, 2006;Li et al, 2019;Sun et al, 2020). In addition, the survival rate (93.33%), weight gain rate, and specific growth rate of U. unicinctus juveniles in this study were higher than the previous reports with survival rates from 65.37% to 82.67% at 30‰ salinity (Chen et al, 2020;Chen et al, 2021) which may result from the different diet of the feeding trial. The diet in this study was composed of Spirulina and Saccharomyces cerevisiae which was more suitable for U. unicinctus juvenile growth than the diet of sea mud and powders of Sargassum, Mytilusedulis, and Spirulina in the previous report (Chen et al, 2020;Chen et al, 2021).…”

“…To investigate the variation of intestinal microbial composition under salinity stress at the genus level more comprehensively, the unclassified genus was also analyzed in this study. Similar methods have been used in microbial composition analysis (Chen et al, 2020). The results indicated that the dominant genera of U. unicinctus intestinal microbiota from the 10‰ group were unidentified Legionellaceae (89.67%) and Labrenzia (3.95%); 15‰ and 20‰ groups with Labrenzia (35.93% and 25.77%), unidentified Legionellaceae (25.67% and 7.00%) and unidentified Rhodobacteraceae (7.67% and 10.97%); 30‰ group with Vibrio (50.59%), Shimia (8.98%), and unidentified Rhodobacteraceae (7.33%), whereas in the 40‰ group, the dominant genera were unidentified Rhodobacteraceae (41.33%), Vibrio (11.62%) and Labrenzia (7.73%) (Figure 5).…”

Effects of Stocking Density on the Growth Performance, Physiological Parameters, Antioxidant Status and Lipid Metabolism of Pelteobagrus fulvidraco in the Integrated Rice-Fish Farming System

“…However, prolonged elevation of Cor levels can cause serious cell damage [83]. La is also a crucial biomarker for stress response in aquatic animals [84]. For the juvenile flounder (Paralichthys orbignyanus) raised in tanks, the serum Cor was significantly increased at high stocking density (7.8 kg/m 3 , 15 d) [85].…”

Effects of culture methods on the nutrient levels, physiological characteristics and intestinal microbiota of the innkeeper worm Urechis unicinctus

“…These results indicated that culture method had an obvious effect on the composition of the intestinal microbiota in U. unicinctus. We previously showed that the stocking density and bottom substrate also had significant effects on the intestinal microbiota of U. unicinctus (Chen et al, 2020(Chen et al, , 2021. The intestinal microbiota has been referred to as the 'second genome' of animals, and it is responsible for regulating many biological functions of the host, including the digestion and absorption of nutrients, as well as the immune responses to external stress (Wikoff et al, 2009).…”