Gut microbiota of fast and slow growing grouper Epinephelus coioides

Abstract

Although the gut microbiota of fish has been studied extensively using traditional or molecular techniques, little information is available on the correlation between gut microbiota and growth of host fish. In the present study, the gut microbiota of two groups of juvenile grouper Epinephelus coioides, slow growing (SG) and fast growing (FG) grouper at 75 days post-hatch (DPH), were investigated by using standard isolation and characterization procedures. The results showed that 4 Vibrio specieswere isolated and comprised 12.3% of the total gut bacteria in SG grouper, whereas only two Vibrio species were isolated and comprised 3.6% of the total bacteria in FG grouper. At the same time, Bacillus pumilus, Bacillus clausii and Psychroacter sp. were only isolated and dominated in the gut of FG fish. The 3 species showed antagonistic effect on pathogenic Vibrio, this may cause the lower number and less species of Vibrio in the gut of FG grouper and suggesting fast growing fish might harbor a favorable microbiota. The number of total cultivable aerobic and facultative anaerobic bacteria was similar in the gut of two groups, 5.4×106 CFU/g and 9.0×106CFU/g in SG and FG group, respectively. Besides those most common bacteria such as Vibrio spp., Pseudomonas spp. and Acinetobacter spp., several Gram-positive and Gram-negative bacteria not normally in the gut of marine fish were also isolated from both groups of fish. The bacteria in the gut of grouper could be classified into three groups belonging to γ-proteobacteria, β-proteobacteria and Bacilli class. Key words: Gut microbiota, fast growing grouper, slow growing grouper,Epinephelus coioides