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Reacting to raised levels of RTGE

The warmer summer in 2009 has led to increasing outbreaks of rainbow trout gastro enteritis (RTGE). Reports from farms indicate that the outbreaks are often more severe than in previous years.

Anticipating these events, Skretting in France, Spain and the UK introduced React RTGE, a feed with extra ingredients to support the trout through an RTGE outbreak and to help maintain growth rates.

Frédéric Esnault, a fish vet with Skretting France, says the disease has been building up with the water temperature, especially in the west and southwest of France and more outbreaks were expected at the end of summer because of the combination of raised temperatures and reduced water availability. “The conventional response on the trout farms is to reduce feeding rates, even to introduce periods of fasting. This is preferred to administering antibiotics as they provide only a temporary benefit, often with rapid relapses when the treatment is stopped. RTGE is caused by filamentous bacteria in all parts of the gut of the fish and reducing feed present in the gut reduces the proliferation of the bacteria and thus minimises the symptoms they cause. However, the strategy also reduces the growth rate of the fish, prolonging the time before they are ready for harvest. We formulated React RTGE to include our unique blend of plant extracts which has an inhibitory effect on these bacteria so that feeding rates can be closer to normal.

“Our recommendation is to use slightly lower feed rates and switch between one of our conventional feeds and React RTGE. Two weeks of each feed are separated by one day of fasting. The switching in nutrition and the effects of React RTGE ingredients help to prevent the bacteria from becoming established in the gut of the fish. In trials and with the first customers to adopt this regime we are seeing better growth rates than with trout given only lower rates of conventional feed.”

John Roberts, Product Development Manager in Skretting UK, comments, “The higher growth rate is maintained when the temperature goes above 17 °C if the water is well oxygenated. More robust health is another benefit of React RTGE, as the trout are less susceptible to further infections. React RTGE is a specific feed in our Active Nutrition categorisation of optimised, proactive and specific feeds. It is formulated to help the fish counter the effects of a particular condition, while proactive feeds such as Protec build fish up to withstand imminent stress or a disease outbreak. Protec feeds can be used in anticipation when an outbreak of RTGE is likely.”