Effects of dietary sodium chloride on chloride cell development and growth of rainbow trout

The effects of increased dietary salt on growth and morphology and numbers of chloride cells of rainbow trout (Oncorhynchus mykiss) were investigated using three isonitrogenous and isocaloric diets containing 1.5, 4.5 and 10.5% sodium chloride, respectively. The basal trout diet contained approximately 0.7 - 0.8% sodium chloride; there was no nutrient dilution in any of the diets caused by salt addition.

The added salt did not affect growth rate and food conversion efficiency of the fish The numbers of chloride cells in the interlamellar region decreased significantly as the salt level in the diet increased, while the numbers of chloride cells at the base of the lamella increased only slightly with the increase of salt level. The total chloride cell numbers, including cells in the interlamellar region and at the base of the lamella, increased somewhat as the salt level in the diet increased. Fish fed on 4.5% and 10.5% of salt had significantly higher numbers of chloride cells than those of fish fed on the control diet after six weeks of feeding. The size of chloride cells at the base of the lamella did not differ among different treatment groups. Total numbers of chloride cells in fish fed 4.5 and 10.5% NaCl were significantly higher than the control groups; however, there were no statistical differences among the treatment diet groups with regard to chloride cell numbers. It was concluded that the dietary salt did not significantly affect either the fish growth or chloride cell size of yearling rainbow trout.