Correlation between dietary lipid:protein ratios and plasma growth and thyroid hormone levels in juvenile Arctic charr, Salvelinus alpinus (Linnaeus)

Cameron, C.; Gurure, R.; Reddy, K.; Moccia, R.; Leatherland, J.

doi:10.1046/j.1365-2109.2002.00683.x

Sexually immature Arctic charr, Salvelinus alpinus (Linnaeus), were fed one of five isoenergetic practical diets of differing lipid:protein ratios (0.98, 0.67, 0.41, 0.26, 0.19) for an 84-day period to examine the influence of diet composition on growth, and growth hormone (GH) and thyroid hormone physiology. All five diets supported growth at approximately the same rate, but the diet with a lipid:protein ratio of 0.98 had the lowest weight gain and highest food conversion ratios. A GH enzyme-linked immunosorbent assay (ELISA), developed for use with oncorhynchid fishes, was validated for use with Arctic charr. Plasma GH concentrations were significantly higher in fish fed the diet with a lipid:protein ratio of 0.98, and there were significant direct and inverse correlations between plasma GH levels and dietary lipid and protein content respectively. There were no significant differences in pre- and post-prandial plasma GH concentrations for any group. There were significant post-prandial elevations of plasma triiodothyronine (T3) and thyroxine (T4) for fish fed the lower lipid:protein ratio diets, but there were no differences related to the diets. The results are discussed in terms of GH as a factor in the regulation of lipid and protein homeostasis in fishes.