2010/771 Alleviation of Summer Gut Syndrome in Tasmanian Atlantic Salmon

By Christina Neuman

Atlantic Salmon farmed in south-eastern waters of Tasmania have been reported to experience clinical symptoms during periods of high water temperature, including loss of appetite and diarrhoea resulting in underweight fish. The symptoms have collectively been referred to as summer gut syndrome (SGS) and it is believed to be of bacterial origin as antibiotic treatment, in combination with a change in diet, temporarily alleviated these symptoms. This project investigated the impact of two commercially available diets and environmental water temperature on the hindgut bacterial populations of farmed Atlantic Salmon, over a 10-month production period, between July 2010 and May 2011. A novel approach was employed to analyse the functional status of the gut microbial community and their ability to break down various substrates. The project also investigated the presence and characteristics of lactic acid bacteria (LAB) in the gut of healthy salmon, and evaluated their usefulness as a probiotic candidate in vitro.

Results showed that an increase in the seawater temperature from 10°C to 18.5°C had a greater impact on the gut microbiota than either of the two commercial feeds given to the fish. The effectiveness of a semi-continuous culture fermenter to assess differently formulated fish feeds on the growth of the salmon gut microbiota was also tested. The results showed changes in the composition of the fermenter microbiota similar to those observed in the farmed fish with an increased level of Vibrio species and a decreased number of LAB.

T

hese data suggests that for Atlantic Salmon, water temperature is the most important factor influencing the gut microbiota during summer months. Considering the gut microbiota has a major role in the health of the fish, any changes to its composition may allow for the overgrowth of opportunistic pathogens and development of diseases under favourable conditions. An improved formulation of the fish feed alone or in combination with LAB strains, such as those identified in this project, may help the stability of the gut microbiota of salmon at high water temperatures.