The Characteristics of Culturable Bacterial Microflora in the Gastrointestinal Tract of Turbot (Scophthatmus maximus) Larvae

Abstract:

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 16S rDNA for alignment with NCBI 16S rDNA 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 (P<0.01). Similarly, vibrio counts were increased initially and then tended toward stable. Day 17 is the cutoff for the significant differences (P<0.05). 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.