The effects of environmental stress on the physiology of growth in rainbow trout, Salmo gairderi Richardson

There is little doubt that both mammalian and teleost growth hormones can accelerate growth and increase food conversion efficiency in all commonly-reared species of salmonid fish. In those vertebrates that have been closely studied (predominantly mammals), the pituitary hormone somatotropin (GH or growth hormone) is a prime determinant of somatic growth. The hormone stimulates protein biosynthesis and tissue growth, enhances lipid utilization and lipid release from the adipose tissues (a protein-sparing effect) and suppresses the peripheral utilization of glucose. The present study is a prerequisite for future work on growth hormone physiology in salmonids and should contribute to our understanding of the mechanisms of growth suppression in stressed fish. Plasma growth hormone (GH) levels were measured in rainbow trout using a radioimmunoassay developed against chinook salmon growth hormone

Directional bias of illusory stream caused by relative motion adaptation

AbstractEnigma is an op-art painting that elicits an illusion of rotational streaming motion. In the present study, we tested whether adaptation to various motion configurations that included relative motion components could be reflected in the directional bias of the illusory stream. First, participants viewed the center of a rotating Enigma stimulus for adaptation. There was no physical motion on the ring area. During the adaptation period, the illusory stream on the ring was mainly seen in the direction opposite to that of the physical rotation. After the physical rotation stopped, the illusory stream on the ring was mainly seen in the same direction as that of the preceding physical rotation. Moreover, adapting to strong relative motion induced a strong bias in the illusory motion direction in the subsequently presented static Enigma stimulus. The results suggest that relative motion detectors corresponding to the ring area may produce the illusory stream of Enigma

Differences in the sensitivity of brown trout, Salmo trutta L., and rainbow trout, Salmo gairdneri Richardson, to physiological doses of cortisol

Interspecific differences in the stress response of fish may be due, in part, to differences in the sensitivity of target tissues to cortisol. The relative response of brown and rainbow trout to a standardized dose of cortisol was assessed by monitoring condition (K factor), the number of circulating lymphocytes and mortality due to disease, following cortisol treatment. Cortisol implantation resulted in a significant decline in K factor and number of circulating lymphocytes in immature brown trout, but not in immature rainbow trout, despite plasma cortisol levels being similar in both cases. Cortisol implantation in mature brown and rainbow trout significantly increased the mortality rate due to bacterial and fungal infection compared with control fish. Furthermore, the mortality rate due to disease was significantly greater in brown trout than rainbow trout, despite both groups receiving similar doses of steroid

The deleterious effects of cortisol implantation on reproductive function in two species of trout, Salmo trutta L and Salmo gairdneri Richardson

Implantation of a cortisol-releasing pellet (60 mg/kg fish) into the peritoneal cavity of brown trout, Salmo trutta L. (sexually maturing males and females), and rainbow trout, Salmo gairdneri Richardson (maturing males and immature fish of both sexes), significantly elevated their plasma cortisol level. At 18 days postimplantation, cortisol-implanted sexually maturing male brown trout had smaller gonads, a lower plasma testosterone level, and less gonadotropin in their pituitary gland than control fish. Plasma levels of 11-ketotestosterone and gonadotropin were not significantly affected. Cortisol-implanted sexually maturing female brown trout had smaller gonads, reduced plasma levels of 17β-oestradiol, testosterone, and vitellogenin, and a lower pituitary gland gonadotropin content than control fish. The plasma gonadotropin level was unaffected. At 36 days post-implantation, cortisol treatment of maturing male rainbow trout significantly suppressed plasma gonadotropin levels. Plasma levels of testosterone, 11-ketotestosterone, and 17α,20β-dihydroxy-4-pregnen-3-one, pituitary gonadotropin content, and gonad size were not significantly affected. In sexually immature female rainbow trout, cortisol administration suppressed the level of vitellogenin in the plasma, compared to control-implanted fish. The 17β-oestradiol level was not affected. Cortisol implantation did not affect the plasma testosterone level in sexually immature male trout. These results suggest that prolonged elevation of plasma cortisol, to levels well within physiological range, can affect a wide range of reproductive parameters in both brown and rainbow trout. Further, some effects are manifest in immature as well as in mature fish. These findings are discussed in relation to the effects of cortisol treatment on the state of health of the treated fish

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

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 store

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

The acute stress of handling followed by confinement for a period of 1 or 24 hr caused a typical stress response in rainbow trout (elevation of plasma ACTH and cortisol) and a significant reduction in the concentration of circulating growth hormone. The chronic stress of low oxygen levels in both crowded and uncrowded tanks of fish caused a significant elevation of circulating GH levels, an effect which was abolished by the provision of additional aeration to the rearing tanks. This chronic elevation of GH levels was closely correlated with an elevation of plasma cortisol in the same fish. These findings are discussed in relation to stress-induced growth suppression and to the links between the hypothalamic-pituitary-interrenal axis and somatotrope activity

Plasma growth hormone levels during sexual maturation in diploid and triploid rainbow trout (Oncorhynchus mykiss)

International audiencePlasma growth hormone concentrations were determined in diploid and triploid rainbow trout of both sexes during sexual maturation. Diploid females grow large ovaries, whereas triploid female trout show no ovarian development. The plasma growth hormone concentration in triploid female trout remained low and unchanged throughout the study, whereas it rose slightly, but significantly, in the diploid females that matured, but not in those that remained immature. On the other hand, triploid males do develop tests like their diploid counterparts. In both groups spermiation was accompanied by a steady rise in the plasma growth hormone concentration. The results suggest that the elevated growth hormone concentration in mature male trout was a consequence not of reproduction per se, but of the loss of condition that accompanied spawning. This hypothesis was supported by the results from the females. Apart from a temporary loss in the mature diploids caused by stripping of the eggs, female trout did not lose condition, neither did they show any change in the plasma growth hormone concentration during the period when they ovulated. These results suggest that it was the nutritional insufficiency accompanying reproduction in male fish that caused the elevation in growth hormone concentration. In fact, a strong negative correlation between the plasma growth hormone concentration and the condition factor of the fish was observed