Dietary lipid composition affects the gene expression of gill Na+/K+-ATPase α1b but not the α1a isoform in juvenile fall chinook salmon (Oncorhynchus tshawytscha)

We assessed the effects of dietary fatty acid composition on sodium–potassium ATPase (Na+/K+-ATPase) activity and isoform expression in the gills of juvenile fall chinook salmon, Oncorhynchus tshawytscha by supplementing diets with either anchovy oil (AO) or AO blended with canola oil (CO) so that CO comprised 0% (0CO), 11% (11CO), 22% (22CO), 33% (33CO), 43% (43CO), or 54% (54CO) of the measured dietary lipid content. The effects of diet were assessed in freshwater (FW) following 104 days of diet manipulation, in response to 24-h seawater (SW) transfer at this time, and following an additional 35 days of SW acclimation. Gill Na+/K+-ATPase activity was not significantly affected by diet at any sampling time, and there were no consistent effects of diet on the expression of the Na+/K+-ATPase α1a isoform. As dietary CO increased, Na+/K+-ATPase α1b mRNA decreased in fish held in FW, with the 43CO and 54CO diet groups having significantly lower levels than fish fed the 0CO and 11CO diets. Twenty-four-hour SW challenge did not affect the expression of the Na+/K+-ATPase α1a isoform in any diet group, but this isoform was down-regulated in all diet groups following 35 days of SW acclimation. Na+/K+-ATPase α1b expression levels increased in response to 24-h SW transfer and SW acclimation only in fish fed the 54CO diet. The effects of the two extreme diets (0CO and 54CO) were also assessed at various time points during 104 days of rearing in FW. Na+/K+-ATPase α1b mRNA levels were greater in fish fed diet 0CO versus those fed diet 54CO at all times during the FW culture period. These data demonstrate that dietary fatty acid composition can influence the gill Na+/K+-ATPase isoform physiology of juvenile fall-run chinook salmon prior to SW transfer.