Aerobic, heterotrophic gastrointestinal microflora of tropical marine fishes

The aerobic/facultatively anaerobic bacterial flora of the gastrointestinal tract of four tropical marine fishes, representing differing nutritional habits, was investigated. Populations of marine bacteria in the coral trout (Plectropomus leopardus), a carnivore, were variable and not clearly related to the presence of food in the intestinal tract. For the planktivore Caesio erythrogaster, and the detritivore (Ctenochaetus striatus), up to 108 bacteria were detected per gram of gastrointestinal contents, and the population size remained relatively constant throughout the intestinal length. Vibrio species, particularly V. harveyi and V. damsela, dominated the microbial populations in all of the above fish. The intestinal microflora of the herbivore Acanthurus nigrofuscus was markedly different from the other fish examined. Stomach contents were devoid of culturable bacteria and the intestinal tract was dominated (in some cases up to 100%) by agar digesting non-Vibrio bacteria. These results are discussed in relation to the possible role of marine bacteria in digestive and nutritional processes in tropical marine fishes