The effect of starvation on growth and plasma growth hormone concentrations of rainbow trout, Oncorhynchus mykiss

Abstract

Two experiments, one using 0+ the other 1 + rainbow trout, were conducted to investigate the effect of prolonged starvation on plasma growth hormone levels. The results from both experiments were essentially the same. As expected, starvation resulted in cessation of growth and in a lower coefficient of condition, whereas fed fish continued to grow and remained in good condition. Starvation had relatively little effect on the plasma cortisol level; in one experiment levels were elevated temporarily in starved fish, although by the end of the experiment there was no longer any difference between starved and fed fish, and in the other experiment plasma cortisol levels remained very low throughout the course of the experiment in both starved and fed fish. In contrast, in both experiments starvation had a pronounced effect on the plasma growth hormone level, which rose steadily during both experiments, such that it was six times higher after 1 month of starvation in 0+ fish. and five times higher after 6 weeks of starvation in 1 + fish. Thus, paradoxically, fed fish had very low plasma growth hormone levels and grew rapidly, whereas starved fish had elevated plasma growth hormone levels but did not grow. In both experiments a strong negative correlation was observed between the plasma growth hormone level and the coefficient of condition of the fish. The results are discussed with regard to the well-established metabolic changes that occur during starvation, and it is suggested that a major role of growth hormone during starvation is to aid in the mobilisation of fatty acids and glycerol from adipose stores.

Effects of acute and chronic stress on the levels of circulating growth hormone in the rainbow trout, Oncorhynchus mykiss

“…Although low, it seems likely that variations in GH levels of the magnitude observed in the present investigation (up to IO-fold differences between individual control and stressed fish) are of physiological significance to the fish. The basal level of GH in the blood of rapidly growing trout is of a similar level to that observed here (see Sumpter et al, 1991, for data on rapidly growing diploid and triploid rainbow trout). A further factor worth taking into account when considering the results of Experiments 1 and 2 is that of the mode of GH release.…”

Sequence, genomic organization and expression of ghrelin receptor in grass carp, Ctenopharyngodon idellus

“…Plasma GH levels were significantly increased after starvation in contrast with the control group, and showed the same trend with previous studies (Sumpter et al, 1991;Johnsson et al, 1996;Company et al, 1999;Pierce et al, 2005;Jönsson et al, 2007). The increased plasma GH levels correlated positively with ghrelin and GHS-R1a mRNA expression levels in the pituitary during fasting of the grass carp in the current study, but are not in support of previous observations of decreased plasma ghrelin levels in fasted rainbow trout, may be due to differences in various physiological as well as physical parameters (Jönsson et al, 2007).…”

The effects of diet composition and ration on biotransformation enzymes and stress parameters in rainbow trout, Oncorhynchus mykiss

“…All of these factors could lead to consumption of suboptimal prey and reduced energy conversion (Higgs et al, 1995). During these periods of reduced feeding, fish must rely on their internal stores of energy to survive and subsequently may experience reduced growth rates (Sumpter et al, 1991).…”