Research progress in function, influence factor and 

application of intestinal flora of shrimp

DING Lan1, XU Shengnan1, LUO Jinping2, GAO Quanxin2

（1. Bureau of Agriculture and Rural Affairs of Anji County, Huzhou Zhejiang313300, China;

 2. College of Life Science, Huzhou University, Huzhou Zhejiang313000, China）

Abstract: There are a large number and a wide variety of bacteria in shrimp intestines, which play important roles in nutrient absorption, growth and development and disease defense. Intestinal bacteria are the main members of intestinal microorganisms, which have been found to be closely related to growth stage, individual size and health status of shrimp. Moreover, once the dynamic balance of intestinal flora of shrimp deviates from the normal and healthy range, the shrimp will exhibit metabolic abnormalities and tissue lesions, leading to the invasion of pathogenic microorganisms. With the continuous deepening of research, experts and scholars at home and abroad have begun to explore the unknown functions of shrimp intestinal microflora and made much progress in recent years, mainly involving growth and development, environmental stress, disease occurrence, feed nutrition, and water quality conditions. During the entire development process of shrimp, the structure of intestinal microflora undergoes significant changes. Intestinal microflora can be adjusted based on shrimp feed, feeding patterns, and nutrient requirements for growth and development, so the dynamic balance of symbiosis is more beneficial to both parties, thereby promoting shrimp growth. The abundance of Actinobacteria significantly increases with the extension of culture time of Litopenaeus vannamei, while αProteobacteria showes an opposite trend of change. γProteobacteria is the dominant bacteria in healthy shrimp, accounting for 40% of L. vannamei and 90% of Penaeus monodon. During the early development stage of P. monodon, Proteobacteria dominates, but Actinomycetes becomes the dominant bacteria in the intestinal tract of adult shrimp. γ and α Proteobacteria and Flavobacteria are the dominant microflora of L. vannamei at different stages of early development. During the larval stage of L. vannamei, Vibrionaceae occupies an absolute advantage in the intestinal flora, but in juvenile and adult stages, Rhodobacteraceae gradually replaces Vibrionaceae as the dominant bacteria. In the early stage, the intestinal microflora of shrimp is variable, but in the later stage of development, it is relatively stable. In order to coexist with the host, the intestinal microflora of healthy shrimp regards pathogenic microorganisms as invasive species. Once the balance of intestinal flora changes significantly, harmful microorganisms will seize the opportunity to invade, leading to disease of host. There is a significant correlation between the intestinal microflora structure of shrimp and the outbreak of diseases. After an outbreak of disease, the normal activity of the intestinal microflora of L. vannamei is abnormal and presents a relatively disordered state. In recent years, experts and scholars have proposed the concept of microbiotaforage Z scores (MAZ), which is a time variant index of intestinal microflora based on the age of the host. MAZ is relatively stable in healthy shrimp, but once diseases occur, MAZ will decline sharply. Therefore, analysis of the structure of host intestinal microflora can assess the health level and susceptibility to pathogens. The core microflora of healthy shrimp is generally dominated by the orders Verrucomicrobiales and Alteromonadales, but during the outbreak of disease, the core microflora gradually shifts to a structure with the orders Rhodobacterales, Vibrionales, and Flavobacteria. There is a significant positive correlation between the immune status of shrimp and relative abundance of intestinal core flora. In order to make the dynamic balance of the intestinal flora and its symbiotic state with the host more conducive to adapting to changes in the external environment, the shrimp intestinal flora can be changed according to environmental conditions of water (ammonia nitrogen, water temperature, salinity, pH, etc.). As an important ecological factor, salinity is crucial for the growth of cultured shrimp. The intestinal microflora of L. vannamei is closely related to the salinity of water. In highly saline water, multiple conditional pathogens in the intestinal tract increases, leading to a sharp decline in the health level of the shrimp. With the continuous changes of salinity, conditional pathogenic bacteria increase and beneficial bacteria decrease, indicating that continuous changes in salinity can lead to serious imbalance in the structure of intestinal flora and may lead to intestinal dysfunction. Research on the response mechanism of salinity stress to P. monodon has shown that the abundance of Vibrio in high salinity group is higher than that in low salinity group, while the abundance of Shewanella in low salinity group is higher than that in high salinity group. Based on the theory of coevolution, it can be inferred that the interaction between shrimp and its intestinal flora is formed through longterm coevolution, and this symbiotic mechanism can ensure the colonization and reproduction of intestinal bacteria. In other words, the evolution of shrimp intestinal microflora follows Darwin’s law of evolutionary dynamics, and shrimp host and their intestinal microflora must adapt to each other to survive. Establishing criteria for the intestinal microflora of healthy shrimp at different stages of development will help to assess the health level and development status of shrimp. The growth and development, phenotypic traits, and stress resistance characteristics of shrimp are closely related to the composition and structure of intestinal microflora. Therefore, establishing a relationship model between economic traits and intestinal microflora using bioinformatics, macrogenomics and molecular biology will be helpful in improving economic traits and productivity through optimizing the microflora structure. China is recognized as a major shrimp production and consumption country in the world, but there are many problems in China’s shrimp industry, such as frequent disease outbreaks, low feed utilization, and water environmental pollution. Intestinal microflora as a symbiotic partner of shrimp has become the focus of research on healthy shrimp farming. In the process of shrimp culture, it is necessary to rationally mix the nutritional components of the diet at different stages of development to fully utilize the beneficial functions of intestinal flora, thereby promoting intestinal health. Therefore, it is necessary to build a shrimp specific intestinal bacterial strain bank and develop shrimp specific probiotic preparations. In general, the beneficial function of intestinal microflora has been widely recognized, but precise microflora regulation technology is still in the initial stage. An indepth understanding of the functional characteristics of intestinal flora can lay an important theoretical foundation for the healthy culture of shrimp and improve the production capacity and development and utilization of probiotics. This paper briefly describes the relationship between intestinal flora and growth and development, and disease occurrence. And the effects of feed nutrition and environmental stress on the intestinal flora of shrimp are further reviewed. Finally, this paper looks forward to the research and application trend of shrimp intestinal flora. The paper provides scientific basis for exploring the function of intestinal microbiota, improving shrimp intestinal nutritional health and developing new functional intestinal probiotics.

Keywords: shrimp; intestinal flora; phenotypic traits; environmental stress