Effects of Dietary Allicin on the Growth, Digestion, Non-Specific Immunity, and Gut Microbiota of Sea Cucumber (Apostichopus japonicus)

Abstract

Sea cucumber (Apostichopus japonicus) is an important marine aquaculture species in China. In 2022, the total area of sea cucumber aquaculture in China reached > 3.7 million acres, with a breeding yield of 24.85 tons. Sea cucumber aquaculture is the largest single variety of marine aquaculture species in China. With the increase of sea cucumber aquaculture scale and density, its feeding efficiency is low, which leads to low utilization rate of feed. It is easy to cause residual bait to mold and decay, polluting water quality and leading to frequent sea cucumber diseases. Therefore, antibiotic abuse has become abundant. However, the extensive use of antibiotic drugs poses ecological and food safety risks. Therefore, developing environmentally friendly and healthy feed additives that have feeding, antibacterial, and immune enhancing effects is urgently required. Our research group screened various sea cucumber attractants in the early stage and selected allicin for further feeding experiments based on the initial experimental results. To investigate the effects of adding allicin to feed on the growth, digestion, immune performance, and gut microbiota structure of sea cucumber (Apostichopus japonicus), healthy sea cucumber with an initial body weight of (50.25±3.21) g was used as the research object. Feed supplemented with 0% (control), 0.2%, 0.4%, and 0.6% allicin was used as feed for 45 days. The growth rate, immune and digestive enzyme indicators, as well as differences in gut microbiota structure of different experimental groups were determined. Weight gain and specific growth rates of the experimental group with added allicin were significantly higher than those of the control group (P < 0.05), with the weight gain rate and specific growth rate of the group with added 0.4% allicin being (29.49±2.07)% and (0.57±0.13)%/d, respectively, significantly higher than the other groups (P < 0.05). As the amount of allicin added increases, the activities of digestive enzymes such as trypsin, amylase, and lipase, as well as non-specific immune enzyme activities such as alkaline phosphatase, acid phosphatase, lysozyme, and superoxide dismutase in body fluid, all showed a trend of first increasing and then decreasing. Except for the ACP index, the digestion enzyme and non-specific immune enzyme activities of the 0.4% experimental group were significantly higher than those of the other groups (P < 0.05). There was no significant difference in the number of OTUs in the gut microbiota of sea cucumber. The Chao1 index showed a trend of first increasing and then decreasing with the increase of allicin addition, while diversity indices such as ACE, Shannon, and Simpson indices showed a decreasing trend with the increase of allicin addition. The diversity index of the 0.6% experimental group was the smallest. The addition of allicin affected the gut microbiota structure of sea cucumber, with an increasing trend in the abundance of Rhodobacter, a decreasing trend in the abundance of Escherichia coli, and an initial increase followed by a decrease in the abundance of Clostridium. When the allicin addition was 0.6%, the microbial community structure changed significantly (P < 0.05). LEfSe analysis showed that Chitinophagales, Ruminococcacaea, Gardnerella, and Bifidobacteriales were significantly dominant bacteria in the control group (P < 0.05), indicating that these bacteria were significantly inhibited with the addition of allicin. The research results indicate that adding an appropriate amount of allicin to feed can improve the growth performance of sea cucumber, promote digestive and non-specific immune enzyme activity, increase the abundance of beneficial bacteria while inhibiting the proliferation of harmful bacteria, and change the structure of sea cucumber gut microbiota. The appropriate amount of allicin added to feed was 0.4%. To our knowledge, this is the first report to demonstrate the effect of different garlic concentrations on the growth performance and intestinal microbiota of sea cucumber. Dietary garlic supplementation was intestinal microbiota for sea cucumber when administered as feed additive in terms of promoting growth and inducing changes in the intestinal microbiota. Finally, our research findings suggest that dietary garlic supplementation may represent an antibiotic as growth promoter in aquaculture.

Keywords

• sea cucumber
• allicin
• gut microbial structure
• enzyme activity