Effects of dietary testosterone on growth and sex ratio in juvenile Atlantic salmon (Salmo salar)

Diets to which testosterone (1 or 10 ng/g diet) had been added were fed to juvenile Atlantic salmon (Salmo salar) for nine months beginning for months after hatching (Experiment 1) and upon completion of yolk absorption (Experiment 2) to determine the effects on growth, gonadal development, and sex ratio. Dietary testosterone at 10 ng/g fed to juvenile salmon at four months after hatching (Exp. 1) induced significant changes in condition factor (0.69±0.01) compared to controls (0.79±0.01) at the end of the test period. In both experiments, salmon treated with 10 ng/g diet induced a significantly higher percentage of male fish compared to controls. Dietary testosterone at 1 ng/g fed to juvenile salmon beginning four months after hatching induced significant increases in weight (18.95±0.99) and length (13.58±0.23) compared to controls (14.55±1.50 and 11.94±0.43, respectively). In Experiment 1 or 2, there was no apparent influence of dietary testosterone on precocious male sexual development. Dietary testosterone at 1 or 10 ng/g fed to juvenile salmon upon completion of yolk absorption (Exp. 2) induced no consistent changes in growth in juvenile Atlantic salmon. These studies indicate that low levels of dietary testosterone may influence physiological responses in juvenile Atlantic salmon dependent upon timing of treatment.

Use of an immobilized enzyme reactor for the analysis of residues of 17 alpha-methyltestosterone in trout by high-performance liquid chromatography

We have recently observed in trout that 48 h after ingestion of a single dose of [14C]-17 alpha-methyltestosterone ([14C]-MT), 25% of the radioactivity was still in the carcass, corresponding to metabolites of 17-MT. These compounds have no appreciable chromophore, fluorophore or electrophore, therefore the usual detection systems was not satisfactory for their analysis. Consequently a method was developed for high-performance liquid chromatographic separation and detection of two of the major tissue metabolites of 17-MT: 5 alpha-androstane-17 alpha-methyl-3 alpha,17 beta-diol and 5 beta-androstane-17 alpha-methyl-3 alpha,17 beta-diol. A column of immobilized 3 alpha-hydroxysteroid dehydrogenase was prepared and used for detection. The NADH produced from 3-hydroxysteroids by this immobilized enzyme reactor was monitored fluorimetrically. The detection limit of this method, as obtained from the calibration curve, was at the picomole level; the limit of quantification in muscle was 1 microgram/kg, at a signal-to-noise ratio of 4.

Interaction "nutrition-reproduction" in fish

In wild fish, gonad maturation and spawning induce modifications in feeding behaviour and dynamics of body stores which are possibly responsible for metabolic disorders. Conversely, food manipulations can modify reproduction of captive female broodstock. A restricted diet during early stages of the life cycle delays the first maturation age, a quantitatively restricted food supply during the stages of oocyte differentiation reduces the egg number, while a reduction of food levels during the last phases of oogenesis has only a small effect on egg size, composition and hatchability. During the spawning period, salmonid female broodstock seem to be more able to utilize carbohydrates than immature fish, they valorize the energy brought in by fats and have low quantitative requirements for proteins (28%). On the other hand, Red Sea bream broodstock have higher needs for proteins (45%).The incorporation into diet of liposoluble vitamins and essential fatty acids is necessary for normal reproduction, but (n-6) fatty acids seem to play a more important role than in juveniles. Although the effects and physiological role of carotenoids are not yet well known in salmonids, they are necessary for normal development in Red Sea bream. Although little work has been done on the effects of mineral nutrition, special attention must be paid to trace elements, manganese in particular.The major part of this review concerns female broodstock, since very little interest has been devoted to males.

Cytological Changes in the Pituitary Gland of the Adult Sockeye Salmon (Oncorhynchus nerka) after Gonadectomy

Effects of gonadectomy on the cytological structure of the pituitary gland of sockeye salmon were investigated. Castration of fully grown, but sexually immature, fish appeared to prevent differentiation of any periodic acid–Schiff (PAS) positive cells. On the other hand, castration of mature sockeye induced degranulation of this cell type. These cells later disintegrated. Although the acidophil cells of the proximal pars distalis in the immature castrates showed an apparent increase in number, those in the gonadectomized ripe fish exhibited marked hyperplasia and hypertrophy. In view of the "rejuvenation," including the considerable increase in body weight that occurs after castration of sexually ripe sockeye, it is thought that the changes in the acidophils noted in this experiment may reflect an increased production of growth hormone. Where the gonadectomy was incomplete it was noted that very small remnants of gonad were able to induce, or maintain, all the external secondary characteristics of full sexual maturity. The pituitary of these fish exhibited cytological features intermediate between those of the controls and the complete castrates.

Effect of Metopirone on Pituitary–Interrenal Function in Two Teleosts, Sockeye Salmon (Oncorhynchus nerka) and Rainbow Trout (Salmo gairdneri)

Metopirone (SU 4885), an inhibitor of 11β-hydroxylation of adrenocorticosteroids, was administered intramuscularly to adult castrated sockeye salmon (Oncorhynchus nerka) and intact rainbow trout (Salmo gairdneri). Marked hypertrophy of interrenal cells pointed to an increase in the activity of the interrenal tissue of both species. Increased cortisol concentrations in trout at low dosage levels of metopirone suggested that the drug was stressful. However, decreased concentrations at higher dosage levels in trout, and decreased cortisol concentrations in all salmon indicated that the drug was also exerting a marked inhibitory effect on 11β-hydroxylation. In salmon, a repository ACTH preparation (acthar) brought about interrenal hypertrophy similar to that produced by metopirone. Metopirone also induced degranulation and hyperplasia of the cells of the palisade-like layer in the rostral region of the pars distalis in both species of fish. These cells were the only cell type of the pars distalis that were stained with lead-haematoxylin. The evidence indicates that they are the corticotrops.