Effects of dietary ascorbic acid levels on the growth, energy budget, and immunological performance of green, white, and purple color morphs of the sea cucumber, Apostichopus japonicus

Microplastic fibers transfer from the water to the internal fluid of the sea cucumber Apostichopus japonicus

Microplastics (MPs) are small plastic particles less than 5 mm in diameter. MPs in the form of microfibers (MFs) are widely detected in aquatic habitats and are of high environmental concern. Despite many reports on the effects of MFs on marine animals, their effect on sea cucumbers is still unclear. In addition, our previous filed study has shown that MFs may transfer to the coelomic fluid of the sea cucumber Apostichopus japonicus (A. japonicus). Here, we show how MFs transfer to the coelomic fluid of the sea cucumber. We captured the MFs during their transfer from the water to the coelomic fluid through the respiratory tree. A. japonicus ingested in the MFs along with the water during respiration; the MFs got stuck in the respiratory tree or transferred to the coelomic fluid. The transferred MFs increased during 72 h of exposure and persisted for 72 h after the transfer to clean water. Among the immunity indices, lysozyme (LZM) levels increased in response to the transferred MFs, which confirms the defensive role of LZMs against strange substances. Additionally, non-significantly decreased levels of total antioxidant capacity (T-AOC), malondialdehyde (MDA), peroxidase (POD) and phenol oxidase (PPO) were observed at 24 h and 48 h post-exposure, suggesting minimal oxidative imbalance. Furthermore, there were no significant changes in the speed and the total distance moved by A. japonicus post MFs transfer. This study revealed that MFs transfer and accumulate in the coelomic fluid of A. japonicus.

Regulation of growth, intestinal microbiota, non-specific immune response and disease resistance of sea cucumber Apostichopus japonicus (Selenka) in biofloc systems

Bioflocs are not only a source of supplemental nutrition but also provide substantial probiotic bacteria and bioactive compounds, which play an important role in improving physiological health of aquatic organisms. A 60-day experiment was conducted to investigate the growth, intestinal microbiota, non-specific immune response and disease resistance of sea cucumber in biofloc systems with different carbon sources (glucose, sucrose and starch). Control (no biofloc) and three biofloc systems were set up, and each group has three replicates. The results showed that biofloc volume (BFV) and total suspended solids (TSS) increased in the sequences of glucose > sucrose > starch and green sea cucumber > white sea cucumber during the experiment. The highest specific growth rates (SGRs) were observed in biofloc system with glucose as carbon source, which also had relatively lower glucose, lactate and cortisol levels in coelomic fluid and higher glycogen content in muscle compared to other groups. There were significant increased Bacillus and Lactobacillus counts of sea cucumber intestine in biofloc systems, and the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) also showed obvious ascending trends. Significant increases in total coelomocytes counts (TCC), phagocytosis, respiratory burst, complement C3 content and lysozyme (LSZ) and acid phosphatase (ACP) activities of sea cucumber were all found in biofloc system (glucose). The expression patterns of most immune-related genes (i.e. Hsp90, Hsp70, c-type lectin (CL), toll-like receptor (TLR)) were up-regulated, suggesting the promotion of pathogen recognition ability and immune signaling pathways activation by biofloc. Furthermore, green and white sea cucumber had significantly higher survival rates in biofloc systems during the 14-day challenge test. In conclusion, biofloc technology could improve growth and physiological health of A. japonicus, by optimizing intestinal microbiota, strengthening antioxidant ability, enhancing non-specific immune response and disease resistance against pathogens, meanwhile glucose was recommended as optimal carbon source in biofloc system of sea cucumber culturing.

Growth, blood health, antioxidant status and immune response in juvenile yellow catfish Pelteobagrus fulvidraco exposed to α-ethinylestradiol (EE2)

Triplicate groups of juvenile yellow catfish Pelteobagrus fulvidraco were exposed to three levels of α-ethinylestradiol (EE2) (0, 0.1 and 1 ng L^-1) for 56 days. Fish survival rate (>93.33%) was not different among experimental groups. Weight gain and specific growth rate of fish exposed to EE2 were higher than those of control fish. Hepatosomatic index of fish exposed to 1 ng L^-1 EE2 was the highest. Serum total protein, albumin, globulin, alanine aminotransferase, aspartate transaminase, cholesterol and triglyceride increased with increasing EE2 exposure levels. Liver total anti-oxidative capacity, malondialdehyde content and lysozyme activity of fish exposed to EE2 were higher than those of control fish. Phagocytic indices of fish exposed to 1 ng L^-1 EE2 was lower than that of control fish. This study indicates that although EE2 exposure can promote the growth of yellow catfish in short-term, EE2 exerts its toxic effects by inducing reactive oxygen species generation and malondialdehyde accumulation, leading to blood deterioration and interfering with immune response.