Turbot(Scophthatmus maximus) breeding,especially the larval breeding,has been seriously affected by the bacterial diseases that were caused by the interactions of fish,pathogens and the environment.The gastrointestinal flora is the dominant location for the occurrence of diseases.This study is to analyze the gastrointestinal microflora of turbot larvae and expound their formation and succession.Using conventional bacteriological culture techniques,we isolated and quantified the bacteria from the gastrointestinal tract of turbot larvae,tank inlet water and feed in a turbot breeding farm.The dominant strains were identified by sequencing their 16 S r DNA for alignment with NCBI 16 S r DNA sequences database.The results showed that the total bacteria count in turbot larvae GI tract was increased and then decreased from Day 5 to Day 36.From Day 17 to Day 26,the culturable bacteria in GI tract were approximately 105-106 CFU/g,which showed extremely significant difference compared to the other stages(P0.01).Similarly,vibrio counts were increased initially and then tended toward stable.Day 17 is the cutoff for the significant differences(P0.05).Ultimately,the numbers of total bacteria and vibrio remained stable at 104 CFU/g in GI tract.Naturally,Vibrios were the dominant strains in the GI tract of turbot larvae.These results indicated that the dominant bacterial strains in the GI tract changed significantly at different developmental stages of turbot larvae.The bacteria in biological feeding could obviously impact the microflora formation in GI tract in the early stage of turbot,and that Vibrio ichthyoenteri was the dominant strain in the GI tract.
Turbot(Scophthalmus maximus) is a cold-water marine fish. In recent years, with the expansion and improvement of turbot farming, bacterial disease has severely affected turbot development, especially in larvae. Because the fish have the special requirements for the living environment, disease occurrence is the result of interactions among fish, pathogens, and the environment. The gastrointestinal flora plays an important role in fish growth and development, and is closely related to disease occurrence. Therefore, it is necessary to investigate the gastrointestinal flora of larval fish. In this study, factors that influence gastrointestinal microflora formation and succession in turbot larvae were investigated by high-throughput sequencing. The intestinal tract microflara and their relationships with different development stages(e.g., larvae and fertilized eggs), chlorella, rotifer, artemia, pellet feed, and tank inlet water were analyzed. The results revealed that the intestinal tract microflora of turbot larvae was stable after initial feeding and was directly affected by bacteria in fertilized eggs. Meanwhile, microflora structure was stable during turbot larval development and barely influenced by the bacteria in water and feed. The dominant bacterium was Lactococcus piscium at a relative proportion of up to 45%–65% in larval intestines. In addition, the relative abundance of this bacterium in fertilized eggs reached 10.4%. Basing on these results, we suggest that the gastrointestinal tract of turbot larvae may be selective for the colonized bacteria. Some bacteria in water and feed, such as the Streptococcus sp., Pseudomonas sp., and Carnobacterium sp., can colonize intestines as subdominant strains.
