Supplementing Chitosan Oligosaccharide Positively Affects Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) Fed Dietary Fish Meal Replacement With Cottonseed Protein Concentrate: Effects on Growth, Gut Microbiota, Antioxidant Function and Immune Response

Abstract

Oligosaccharides have recently received much attention from researchers owing to their multiple biological activities. This study was conducted to investigate the effects of a diet with reduced fish meal and chitosan oligosaccharide (COS) supplementation on a hybrid grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂). Seven isonitrogenous and isolipidic types of diet were formulated to feed the groupers for 56 days. To prepare the feed, a reference diet (FM group) containing 55% fish meal was used. Concentrated cottonseed protein (CPC) was used to replace 45% of the fish meal protein, and different COS supplementation levels (0, 0.2%, 0.4, 0.6, 0.8, and 1%) were added. After an 8-week breeding trial, Vibrio harveyi bacteria were injected into the groupers for a 7-day challenge test. The results showed that the FM and COS0.4 groups showed the best growth performance among the groups (p < 0.05); however, there was no significant difference in the survival rate (p > 0.05). Unlike in the FM group, adhesion and breakage of the intestinal plica occurred in the COS0 group. The height and width of the gut fold reached maximum values in the COS0.4 group (p < 0.05). Microbiome sequencing suggested that there was a stable microbiota core in the gut of the groupers. With increasing COS levels, the abundance of both beneficial bacteria and conditional pathogens increased; the activities of serum glucose oxidase, catalase, and total superoxide dismutase also increased (p < 0.05). In the gut tissue, the activities of glutathione peroxidase, glutathione reductase, and glutamine increased first but then decreased (p < 0.05); the contents of lysozyme, acid phosphatase, complements C3 and C4, and IgM showed upward trends (p < 0.05). Compared with that in the FM group, the expression of IL-1β and TNF-α in the COS0 group was upregulated. Gene expression levels of TLR22, TGF-β, and Nrf2 increased first but then decreased with COS supplementation levels (p < 0.05). COS supplementation reduced the cumulative mortality of the groupers in the challenge test (p < 0.05). In general, the results of this study demonstrated that dietary COS supplementation enhanced growth performance, intestinal health, and antioxidant and immune responses of groupers fed with a low-fish meal diet. The optimal and acceptable levels of COS supplement were 0.45 and 0.4–0.6%, respectively; these values can provide a reference for developing aquatic prebiotics.

Effects of Shrimp Shell-Derived Chitosan on Growth, Immunity, Intestinal Morphology, and Gene Expression of Nile Tilapia (Oreochromis niloticus) Reared in a Biofloc System

“…Since the proportion of villi is related to the ability to absorb nutrients through the available surface area, the surface increase could potentially improve nutrient utilization and storage [79]. Our results are consistent with previous studies, such as those showing an increase in villus length following supplementation of hybrid grouper diets with CH oligosaccharides [80] or after supplementation of hybrid catfish diets with mannan oligosaccharides [81]. It has also been reported that various other oligosaccharides can significantly increase villus length in numerous fish species, as shown by 1% galacto-oligosaccharide in the diet for red drum [82] or 2% fructo-oligosaccharide in the diet for bluntnose seabream [83].…”

Effects of Clostridium butyricum on Growth Performance, Intestinal Health, and Disease Resistance of Hybrid Grouper (Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂ ) Fed with Cottonseed Protein Concentrate (CPC) Replacement of Fishmeal

“…Ten fields of view of each section were randomly selected for measurement. In previous research [ 39 ], villus height, villus width, and muscle thickness have been measured as intestinal morphological metrics.…”

Research Progress of the Gut Microbiome in Hybrid Fish

“…Chitosan oligosaccharide (COS) is a new prebiotic, dietary COS supplementation, which improves the growth performance and health status of Scopthalmus maximus [ 154 ], Cyprinus carpio koi [ 155 ], and Oncorhynchus mykiss [ 156 ]. Dietary COS supplementation improved the intestinal health and immune responses of hybrid groupers ( Epinephelus fuscoguttatus ♀ × E. lanceolatus ♂) when fed a low-fish meal diet [ 100 ].…”

“…A previous study revealed that a high concentration of inulin could damage the enterocytes of Salvelinus alpinus [ 157 ]. This may explain why 0.4–0.6% COS supplementation was optimum in hybrid groupers [ 100 ].…”