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

Abstract

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 enzymelinked 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 (T 3 ) and thyroxine (T 4 ) 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.

Influence of plasma lipid changes in response to 17β‐oestradiol stimulation on plasma growth hormone, somatostatin, and thyroid hormone levels in immature rainbow trout

“…Furthermore, the observed plasma GH changes may be in response to the E 2 -induced elevation in plasma total lipid concentrations. This argument is supported by evidence of elevated plasma GH levels in fish fed high lipid diets (Martí-Palanca et al, 1996;Company et al, 1999;Pérez-Sánchez, 2000;Cameron et al, 2001), and the observed influence of ration levels on plasma GH concentrations in fishes (Farbridge et al, 1992). Such a response would be found equally in in vivo and in vitro models, since even in the in vitro model, the donor fish were E 2 -primed before the pituitary glands were harvested.…”

Modulation of fish growth hormone levels by salinity, temperature, pollutants and aquaculture related stress: a review

“…Significantly increased GH amounts were detected in gilthead sea bream fed low protein diets however this was unlikely to be translated into enhanced growth since reduced hepatic GH binding and IGF-1 amounts were also found in gilthead sea bream fed low protein diets (Pérez-Sánchez et al 1995). In addition a diet high in lipid composition has been shown to increase plasma GH levels for rainbow trout (Holloway and Leatherland 1998;Holloway et al 1999), Arctic Charr (Cameron et al 2002) and gilthead sea bream (Martí-Palanca et al 1996;Company et al 1999;Pérez-Sánchez 2000). Two explanations currently exist for elevated plasma GH levels when fish are fed diets high in lipid content.…”

Effects of fasting on temporal changes in plasma concentrations of sex steroids, growth hormone and insulin‐like growth factor I, and reproductive investment in Arctic charr

“…This effect is attributed to reduced feedback inhibition by IGF‐I associated with mobilization of lipid reserves (Björnsson, 1997). In Arctic charr, however, plasma lipids may stimulate GH directly, resulting in higher plasma GH in Arctic charr fed high lipid diets than in Arctic charr fed low lipid diets (Cameron et al ., 2002). It is thus possible that the higher plasma GH of the fed fish in the present study may be a response to increased concentration of plasma or tissue lipids derived from the feed.…”