Rainbow trout (Oncorhynchus mykiss). Photo credit: S. Kamalam.

Rainbow trout (Oncorhynchus mykiss). Photo credit: S. Kamalam.

Thanks to the aquaculture revolution, fish such as trout and salmon are no longer a luxury available to the wealthy alone. However, modern cultivation techniques require that we plunder the oceans to provide the fish-oil and - protein diet that sustains output. ‘In order to improve the sustainability of the aquaculture production for trout (and other farmed fish), it is essential to develop alternative aquafeeds’, say Stephane Panserat and colleagues from the INRA and IFREMER in France. Intrigued by the possibility of developing new carbohydrate-rich fish diets to wean the industry off its dependence on marine fish stocks, the team decided to find out whether the diet experienced by trout larvae could alter their metabolism in later life – in much the same way as adult mammals benefit from the effects of early diet. Could he convert trout that utilise carbohydrates poorly into animals that thrive on a carbohydrate-rich diet by feeding them carbohydrates when young (p. 3396)?

Supplying trout larvae with a high or low carbohydrate diet for 5 days, the team then switched the fish back to a commercial trout feed diet for 100 days before testing their responses to a high carbohydrate diet (28%).

Although the team found alterations in glucose metabolism in the livers of the young fish – known as alevins – that allowed them to process carbohydrates, these changes were not carried through into the juveniles. And when they tested glucose metabolism in the muscles of the juvenile fish, they found that the fish that had been fed a high carbohydrate diet in early life had altered their glucose metabolism, but, paradoxically, the change had left them less able to use glucose as a muscle fuel. The team also tested the effect of the high carbohydrate diet on the gut flora of the fish and found changes in the fungi in the larvae's intestines. Considering the results together, the team concludes that dietary reprogramming is possible, but more work needs to be done to understand the mechanisms of change.

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