Aims: Factors such as seasonal temperature and diet components, for example, fishmeal (FM) inclusion, can influence the composition of the gut microbiota of fish. In this study, we examined changes in the gut bacterial populations, in particular lactic acid bacteria (LAB), of farmed Tasmanian Atlantic salmon in response to different diets, during periods of higher water temperature.

Methods and Results: Between December 2011 and March 2012 hindgut faecal samples were collected from Atlantic salmon from a commercial fish farm in south of Hobart, Tasmania, fed with one of four trial diets containing either high or low FM inclusion levels with or without prebiotics. Overall there was little difference in the cultivatable bacterial populations in response to varying levels of FM and prebiotic supplementation, with LAB counts decreasing in response to increased water temperatures. However, it was observed that the high FM diet supported the presence of LAB in January, when these were not detected in the low FM diets.

Conclusions: Our study indicates that the inclusion of higher amounts of FM rather than the addition of prebiotics has a greater effect on LAB colonization of the gut in Atlantic salmon.

Significance and Impact of the Study: This study highlights the importance of the new fish feeds for promoting salmon health in aquaculture industry.