Beneficial effects of Metschnikowia sp. C14 on growth and intestinal digestive enzymes of juvenile sea cucumber Apostichopus japonicus

The feces of sea urchins as food improves survival, growth, and resistance of small sea cucumbers Apostichopus japonicus in summer

Mass mortality and low growth highly decrease the production efficiency and sustainable aquaculture development of the sea cucumber Apostichopus japonicus in summer. Sea urchin feces was proposed to address the summer problems. A laboratory study was conducted for ~ 5 weeks to investigate survival, food consumption, growth and resistance ability of A. japonicus cultured with the feces of sea urchins fed kelp (KF feces, group KF), the feces of sea urchins fed prepared feed (FF feces, group FF), and the prepared sea cucumber feed (group S) at high temperature (25 °C). The sea cucumbers of group KF had better survival (100%) than those of the group FF (~ 84%), higher CT_max (35.9 °C) than those of the group S (34.5 °C), and the lowest skin ulceration proportion (0%) when  they were exposed to an infectious solution among the three groups. These results suggest that the feces of sea urchins fed kelp is a promising diet for improving the survival and enhancing the resistance in A. japonicus aquaculture in summer. Sea cucumbers fed significantly less FF feces after 24 h of ageing than the fresh FF feces, suggesting this kind of feces became unsuitable for A. japonicus in a short time (within 48 h). However, the 24 h of ageing at 25 °C for the high fiber feces of sea urchins fed kelp had no significant effects on the fecal consumption of sea cucumbers. In the present study, both fecal diets provide better individual growth to sea cucumbers than the prepared feed. Yet, the feces of sea urchins fed kelp provided the highest weight gain rate (WGR) to sea cucumbers. Therefore, the feces of sea urchins fed kelp is a promising food to reduce the mortality, to address the problems of summer, and to achieve higher efficiency in A. japonicus aquaculture in summer.

Dietary fulvic acid supplementation improves the growth performance and immune response of sea cucumber (Apostichopus japonicas)

The present study aims to explore the effects of dietary fulvic acid (FA) supplementation on the growth performance, digestive enzyme activity and immune response of sea cucumber (Apostichopus japonicas). FA was used to replace 0 (control), 0.1, 0.5 and 1 g cellulose in the basic diet of sea cucumber to formulate four experimental feeds with equivalent nitrogen and energy denoted as F0, F0.1, F0.3 and F1, respectively. No significant differences were observed in the survival rate among all groups (P > 0.05). Results show that the body weight gain rate, specific growth rate, intestinal trypsin, amylase and lipase activities, serum superoxide dismutase, catalase, lysozyme, alkaline and acid phosphatase activities and disease resistance ability against the pathogen, Vibrio splendidus of the sea cucumbers fed with FA-containing diets were significantly higher than those of the control group (P < 0.05). The optimum dose of dietary FA supplementation required for the maximum growth of sea cucumber was 0.54 g/kg. Therefore, dietary FA supplementation to the feed of sea cucumber can significantly improve its growth performance immune response.

Adverse effects of dietary virgin (nano)microplastics on growth performance, immune response, and resistance to ammonia stress and pathogen challenge in juvenile sea cucumber Apostichopus japonicus (Selenka)

It has been well documented that micro- and nanoplastics are emerging pollutants in aquatic environments, and their potential toxic effects has attracted widespread concerns. Here, we evaluated the adverse effects of dietary polystyrene nanoplastics and microplastics (PS-N/MPs) on growth performance, oxidative stress induction, immune response, ammonia detoxification, and bacterial pathogen resistance of sea cucumber Apostichopus japonicus. After collection and acclimation, sea cucumbers were randomized into 3 groups (i.e., control, 100 nm PS-NPs and 20 µm PS-MPs at 100 mg kg^-1 diet) for 60-day feeding experiment. Every group contained 360 sea cucumbers which were equally divided into 3 aquaria as biological triplicates. The results showed that the specific growth rate and final weight of the sea cucumbers fed with diets containing PS-N/MPs were significantly lower than those of control group. Dietary virgin PS-N/MPs significantly increased the reactive oxygen species production and malondialdehyde content in coelomic fluid, causing oxidative stress and damage to the growth and development of A. japonicus. During the experiment, 100 nm PS-NPs significantly induced the depletion in cellular and humoral immune parameters. The calculated IBR values based on multi-level biomarkers revealed the size-dependent toxic differences of PS-NPs > PS-MPs. The relative expression levels of GDH and GS mRNA showed first rise and then fall trends after exposure to ammonia, and 100 nm PS-NPs had a more profound impact on suppressing ammonia detoxification compared with 20 µm PS-MPs. Moreover, the expression of Hsp90, Hsp70, CL, TLR, and CASP2 genes were all down-regulated by ammonia exposure. Taken together of IBR results, ammonia stress test and pathogen challenge, we deduced that dietary 100 nm PS-NPs are more potentially hazardous than 20 µm PS-MPs. These findings provide valuable information for understanding the size-dependent toxic effects of PS-N/MPs and early risk warning on marine invertebrates.

Effects of dietary yeast culture on shrimp growth, immune response, intestinal health and disease resistance against Vibrio harveyi

The current study was conducted to evaluate the effects of different levels of yeast culture (YC) supplementation at 0% (YC 0%), 1% (YC 1%), and 2% (YC 2%) on growth, feed conversion ratio, body composition, intestinal morphology, microflora, immune response, and resistance to Vibrio harveyi infection in Litopenaeus vannamei. After 8-weeks feeding trial, the results showed significant improvement (p < .05) in the final weight, weight gain rate, specific growth rate, survival rate and low feed conversion ratio in YC groups than the control. Serum total protein, superoxide dismutase, catalase, alkaline phosphatase, acid phosphatase, lysozyme, and phenol oxidase in shrimps fed diet YC (2%) were significantly higher (p < .05), whereas significantly decreased trend in serum cholesterol, triglyceride, aspartate aminotransferase, and alanine aminotransferase (p < .05) were observed in YC (2%) diet. Proteobacteria, Bacteroidetes, Actinobacteria, and Firmicutes were the core phylum bacteria found in the shrimp intestines. At the genus level, opportunistic pathogenic bacteria, Vibrio was significantly decreased (p < .05) while beneficial bacteria Pseudoalteromonas was increased in YC (2%) group. Intestinal villus height and width in shrimps fed YC diets were significantly improved than the control diet (p < .05). YC groups challenged test significantly showed (p < .05) improved shrimps immune response against V. harveyi infections with YC (2%) recording the highest percentage survival rate (70%). The present study demonstrated that supplementing YC (2%) can improve growth, intestinal microbiota, intestinal morphology, and immune response against V. harveyi infections in L. vannamei.

Use of probiotics in aquaculture of China-a review of the past decade

China is the largest aquaculture producer in the world. Antibiotics were extensively used to ensure the development of the intensive aquaculture; however, the use of antibiotics causes safety- and environment-associated problems. As an alternative strategy to antibiotics, aquatic probiotics have attracted attention. The microbial organisms used as probiotics or tested as potential probiotics in Chinese aquaculture belong to various taxonomic divisions, including Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria and yeast. Moreover, the mixture of probiotic strains and synbiotics are also widely used. Studies on the mode of action of aquatic probiotics have extended our understanding of the probiotic effects, and novel mechanisms have been discovered, such as interference of quorum sensing. However, use of probiotics in Chinese aquaculture is still at an initial stage, and there are potential risks for some probiotic applications in aquaculture. Further regulation and management are required to normalize the production and usage of aquatic probiotics. In this review, we discuss species, effects, and mode of actions of probiotics in Chinese aquaculture since 2008. Challenges and future directions for research are also discussed.

Dietary supplementation of biofloc influences growth performance, physiological stress, antioxidant status and immune response of juvenile sea cucumber Apostichopus japonicus (Selenka)

Bioflocs are rich in various probiotics and bioactive compounds, which play an important role in improving growth and health status of aquatic organisms. A 60-day experiment was conducted to investigate the effects of dietary supplementation of biofloc on growth performance, digestive enzyme activity, physiological stress, antioxidant status, expression of immune-related genes and disease resistance of sea cucumber Apostichopus japonicus. Juvenile sea cucumbers were fed five experimental diets containing graded levels of biofloc from 0% to 20% (referred as B0, B5, B10, B15 and B20, respectively). The results showed that the sea cucumbers at dietary supplementation levels of 10%-15% biofloc had significantly higher specific growth rate (SGR) compared to control group (diet B0). Digestive enzyme activity increased with the increasing of dietary biofloc level, while no significant difference was found between diets B15 and B20. Dietary supplementation of biofloc also had significant influences on physiological stress parameters except for lactate. There was no significant discrepancy in total coelomocytes counts (TCC) in coelomic fluid of sea cucumber between the treatments. Phagocytosis and respiratory burst of cellular immune at 15% and 20% biofloc levels were significantly higher than those of control group. Significant increases in superoxide dismutase (SOD), total nitric oxide synthase (T-NOS), lysozyme (LSZ), acid phosphatase (ACP) and alkaline phosphatase (AKP) activities of sea cucumber were found at highest dietary supplementation level of 20% biofloc. The expression patterns of immune-related genes (i.e., Hsp90, Hsp70, p105, Rel, NOS and LSZ) in tissues of sea cucumber were analyzed between the experimental diets, and a general trend of up-regulation was observed at higher biofloc levels. Furthermore, dietary 10%-20% biofloc significantly reduced cumulative mortality of sea cucumber after being challenged with Vibrio splendidus. In conclusion, dietary supplementation of biofloc could improve growth performance of A. japonicus, by increasing digestive enzyme activity, releasing physiological stress, enhancing immune response and disease resistance of sea cucumber. The suitable supplemental level of approximately 15% biofloc was recommended in the present study.

Individual Apostichopus japonicus fecal microbiome reveals a link with polyhydroxybutyrate producers in host growth gaps

Gut microbiome shapes various aspects of a host’s physiology, but these functions in aquatic animal hosts have yet to be fully investigated. The sea cucumber Apostichopus japonicus Selenka is one such example. The large growth gap in their body size has delayed the development of intensive aquaculture, nevertheless the species is in urgent need of conservation. To understand possible contributions of the gut microbiome to its host’s growth, individual fecal microbiome comparisons were performed. High-throughput 16S rRNA sequencing revealed significantly different microbiota in larger and smaller individuals; Rhodobacterales in particular was the most significantly abundant bacterial group in the larger specimens. Further shotgun metagenome of representative samples revealed a significant abundance of microbiome retaining polyhydroxybutyrate (PHB) metabolism genes in the largest individual. The PHB metabolism reads were potentially derived from Rhodobacterales. These results imply a possible link between microbial PHB producers and potential growth promotion in Deuterostomia marine invertebrates.

Effects of potential probiotic Bacillus cereus EN25 on growth, immunity and disease resistance of juvenile sea cucumber Apostichopus japonicus

This study was conducted to determine effects of potential probiotic Bacillus cereus EN25 (isolated from mud of sea cucumber culturing water bodies) on growth, immunity and disease resistance against Vibrio splendidus infection in juvenile sea cucumbers Apostichopus japonicus. Animals were respectively fed diets with B. cereus EN25 at 0 (control), 10(5), 10(7) and 10(9) CFU/g for 30 days. Results showed that dietary B. cereus EN25 had no significant effects on growth, total coelomocytes counts and acid phosphatase activity of A. japonicus (P > 0.05). Dietary EN25 at 10(7) CFU/g had significantly improved the phagocytosis, respiratory burst activity and total nitric oxide synthase activity of animals (P < 0.05). Compared to control, dietary EN25 at 10(5) or 10(7) CFU/g had no significant effects on superoxide dismutase activity of A. japonicus (P > 0.05), whereas dietary EN25 at 10(9) CFU/g had significantly decreased its activity (P < 0.05). The cumulative mortality after V. splendidus challenge decreased significantly in sea cucumbers fed with EN25 at 10(7) CFU/g (P < 0.05). The present study confirmed dietary B. cereus EN25 at 10(7) CFU/g could significantly improve immunity and disease resistance in juvenile A. japonicus.