The Pacific white shrimp Litopenaeus vannamei is the most important crustacean species in aquaculture, accounting for 70% of the total shrimp production in the world. In the past decade, development of the shrimp industry has been greatly impeded by disease prevalence, poor growth in low salinity inland water, dietary use of plant ingredients, and antibiotic overuse. The animal gut is a vital organ, and most of the gut functions, such as the functions of immunity, health regulation and nutrient absorption, are achieved by bacterial metabolism in the gut. Therefore, understanding the role of the gut microbiota of L. vannamei is important for improving the performance and production of L. vannamei in aquaculture. This paper summarizes the recent advancements in research on the composition of the gut microbiota of L. vannamei, the factors that influence the microbiota, and nutritional manipulation of the gut microbiota. In addition, based on the review, current problems are raised and future studies directed at solving these problems are proposed. Proteobacteria is the core bacterial group found the gut of L. vannamei, but other groups of bacteria can also be beneficial to shrimp health and growth. The abundance of opportunistic pathogenic bacteria in the gut can change with the developmental stage of the shrimp, diet composition, environmental factors, and in the presence of ambient toxicants such as sulfide. Various prebiotics, probiotics isolated from the gut of L. vannamei and other crustacean species, synbiotics and some organic acids have been used as dietary supplements to evaluate the health of L. vannamei farms. These additives have been compared for their roles in regulating shrimp growth and immunity and in shaping the community structure of the gut microbiota. Future studies should focus on understanding the underlying mechanisms between shrimp metabolism and the gut microbiota and on practical applications of dietary additives to solve problems faced by the shrimp industry.

The Pacific white shrimp Litopenaeus vannamei is a euryhaline penaeid species that shows ontogenetic adaptations to salinity, with its larvae inhabiting oceanic environments and postlarvae and juveniles inhabiting estuaries and lagoons. Ontogenetic adaptations to salinity manifest in L. vannamei through strong hyper-osmoregulatory and hypo-osmoregulatory patterns and an ability to tolerate extremely low salinity levels. To understand this adaptive mechanism to salinity stress, RNA-seq was used to compare the transcriptomic response of L. vannamei to changes in salinity from 30 (control) to 3 practical salinity units (psu) for 8 weeks. In total, 26,034 genes were obtained from the hepatopancreas tissue of L. vannamei using the Illumina HiSeq 2000 system, and 855 genes showed significant changes in expression under salinity stress. Eighteen top Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways were significantly involved in physiological responses, particularly in lipid metabolism, including fatty-acid biosynthesis, arachidonic acid metabolism and glycosphingolipid and glycosaminoglycan metabolism. Lipids or fatty acids can reduce osmotic stress in L. vannamei by providing additional energy or changing the membrane structure to allow osmoregulation in relevant organs, such as the gills. Steroid hormone biosynthesis and the phosphonate and phosphinate metabolism pathways were also involved in the adaptation of L. vannamei to low salinity, and the differential expression patterns of 20 randomly selected genes were validated by quantitative real-time PCR (qPCR). This study is the first report on the long-term adaptive transcriptomic response of L. vannamei to low salinity, and the results will further our understanding of the mechanisms underlying osmoregulation in euryhaline crustaceans.

Carbohydrates are the primary energy source in all animal diets and are the least expensive energy source in the diets of aquatic animals. However, the utilization of carbohydrates by aquatic animals is relatively low relative that of terrestrial animals. Compared with those in fish, few studies have examined the nutrition or metabolism of crustacean species. This lack of information is a bottleneck for current research of crustacean physiology, especially that which focuses on nutrition. Specifically, there is a deficiency of research that focuses on glucose transporter proteins (except for glucose transporter (GLUT) family protein), regulators involved in carbohydrate metabolism, and the interaction of different hormones. This paper summarizes the dietary carbohydrate requirements of various crustacean species and reviews the progress of research on carbohydrate utilization and metabolism, with an aim to providing clearer insight into carbohydrate metabolism and laying a theoretical foundation for crustacean physiological research.