Effects of Thiourea Treatment on Sexually Maturing and Gonadectomized Male Sockeye Salmon (Oncorhynchus nerka)

Adult male sockeye salmon in the final stage of sexual maturation were treated with thiourea for periods of 7–14 wk. The treatment produced strong histological thyroid stimulation but no visible effect on spermatogenesis or development of secondary sexual characteristics. The drug did not affect the interrenal hypertrophy that commonly occurs in these salmon, but slightly inhibited the increase in thickness of the skin. Thiourea induced changes in the pars distalis of the pituitary gland, involving several cell-types, including retardation of gonadotrop development.In gonadectomized fish, thiourea affected neither the skin, nor the interrenal tissue. It caused a marked increase in the height of the thyroid epithelium, correlated with hypertrophy, degranulation, and some vacuolization of PAS-positive cells in the dorso-caudal area of the proximal pars distalis of the pituitary gland. Therefore, these last cells are considered thyrotrops.

Effect of ACTH and Salmon Gonadotropin on Interrenal and Thyroid Activity of Gonadectomized Adult Sockeye Salmon (Oncorhynchus nerka)

Injection of a chinook salmon (Oncorhynchus tshawytscha) gonadotropin preparation into gonadectomized sockeye salmon (Oncorhynchus nerka) did not result in any increase in the plasma concentration of cortisol or cortisone, nor did it stimulate the activity of the interrenal tissue. On the other hand, injection of mammalian ACTH (Acthar) did result in an increase in the plasma concentration of cortisol and cortisone, and stimulated the interrenal tissue. The salmon gonadotropin preparation, however, elicited an increase in thyroid activity. The results suggest that in the salmon, ovulation is not caused by gonadotropin induced interrenal corticosteroidogenesis.

The Use of 17 α-methyltestosterone for Promoting Weight Increases in Juvenile Pacific Salmon

The effect of 17 α-methyltestosterone feeding on the weight of juvenile coho salmon (Oncorhynchus kisutch) and on the weight, length, and condition factor of juvenile chinook salmon (O. tshawytscha) was determined. Significant increases in weight and length but not in condition factor were noted at all levels of steroid tested. Coho fed rations containing 10 mg/kg of the steroid for 42 days showed a 29% net weight gain and chinooks fed 1 mg/kg of the hormone for 84 days exhibited a 17% net weight gain over the respective control groups.A marked thickening of the skin was noted in the coho retained on diets containing 10 and 50 mg/kg of the steroid. This alteration was most evident in those fish fed the highest concentrations of hormone for the longest period.In the coho, diets containing 10 or 50 mg/kg of the hormone evoked marked degenerative changes in the testes. Less drastic alterations were noted in the testes of the chinooks retained on the 1 mg/kg test ration for 84 days. No apparent structural changes were noted in the ovary of any of the test fish.

Histological Effects of 11-Ketotestosterone, 17α-Methyltestosterone, Estradiol, Estradiol Cypionate, and Cortisol on the Interrenal Tissue, Thyroid Gland, and Pituitary Gland of Gonadectomized Sockeye Salmon (Oncorhynchus nerka)

Effects of two androgens, two estrogens, and cortisol in gonadectomized sockeye salmon (Oncorhynchus nerka) were investigated. Males were injected with 11-ketotestosterone, 17α-methyltestosterone, or cortisol for 4 or 7 weeks. Females were injected with estradiol, estradiol cypionate, or cortisol for 8 weeks.Both the androgens and the estrogens caused interrenal hypertrophy. The effect of 17α-methyltestosterone was stronger than that of 11-ketotestosterone, and of the two estrogens used, estradiol cypionate exerted the most marked effect. Cortisol brought about a slight atrophy of the interrenal tissue.A pronounced histological activation of the small thyroid follicles was induced by the two androgens. The estrogens exerted no visible effect on the thyroid gland, and cortisol treatment caused a slight reduction in the height of the follicular epithelium.In the gonadectomized control fish of both sexes, gonadotrophs were small and practically all devoid of granules. All four sex steroids induced the appearance of many granulated PAS-positive gonadotrophs, particularly in the anterior part of the proximal pars distalis. This effect is considered on activation of the gonadotrophs. Cortisol administration induced pronounced degranulation and atrophy of the corticotrophs and this effect was strongest in the males. Neither the androgens nor the estrogens visibly affected the corticotrophs.

Effects of Androgens, Estrogens, and Cortisol on the Skin, Stomach, Liver, Pancreas, and Kidney in Gonadectomized Adult Sockeye Salmon (Oncorhynchus nerka)

A study was made of the histological changes occurring in the skin, stomach, liver, pancreas and kidney of adult gonadectomized male and female sockeye salmon in response to hormone treatments. The males received 11-ketotestosterone, 17α-methyltestosterone or cortisol for 4 or 7 weeks, and the females received estradiol, estradiol cypionate, or cortisol for 8 weeks.In the males, androgen injection evoked a highly significant increase in the thickness of the epidermis, a marked atrophy of the stomach, and a degeneration in the liver and kidney. In the pancreas, the exocrine portion showed characteristics of cytolysis in the acini, whereas the islets of Langerhans were hypertrophied. These changes were generally more pronounced after 7 weeks than after 4 but, in the skin, no further increase in the thickening of the epidermis was noted after the 4th week of treatment. No differences between responses of these tissues to 11-ketotestosterone and 17α-methyltestosterosne were detected.Estrogen administration in the females evoked similar, albeit weaker, responses in the skin, stomach, pancreas, and kidney than those recorded in the androgen-treated males. The liver of the females exhibited the characteristics of a hyperactive organ, which probably reflects estrogen-induced vitellogenesis.The effects of cortisol were similar in both sexes: little, if any, change was noted in the skin; atrophy or degeneration was observed in the stomach, liver, kidney, and in the exocrine portion of the pancreas, and the islets of Langerhans were hypertrophied. The cortisol-induced alterations were not, however, as pronounced as those noted in either the androgen- or estrogen-treated fish.These changes are discussed in relation to the changes observed in normal sexually maturing and reproducing Pacific salmon.

Hypertrophy of the Interrenal Tissue in Sexually Maturing Sockeye Salmon (Oncorhynchus nerka) and the Effect of Gonadectomy

Sockeye salmon (Oncorhynchus nerka) develop marked hypertrophy of the interrenal tissue during the period of sexual maturation and spawning. No differences were found between fish held in captivity and those that matured in their natural habitat. Feeding appeared to have an inhibitory effect, but did not prevent the hypertrophy. Gonadectomy of sexually mature fish resulted in a rapid involution of the hyperplastic interrenal tissue. On the other hand, gonadectomy, when performed in an early stage of sexual maturity, prevented the development of interrenal hypertrophy. The interrenal hyperplasia was not accompanied by apparent changes in the ACTH cells of the pituitary gland. Gonadectomy, however, led to increased affinity of these cells for lead-hematoxylin, but this effect did not take place until after interrenal involution had commenced. The results are discussed and it is concluded that the hypertrophy of the interrenal at this time is caused by gonadal hormones, which may act directly on the adrenal homologue without mediation by the pituitary gland.

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.

The Pituitary Gland of the Sockeye (Oncorhynchus nerka) During Sexual Maturation and Spawning

This communication presents the results of a study of the pituitaries of 150 sockeye salmon in various stages of sexual maturation from the time they entered freshwater till after completion of spawning. In the homologue of the adenohypophysis, nine different cell types were distinguished. On the basis of changes in tinctorial and histochemical properties and relative proportions of each of these cells, it was concluded that the sockeye pituitary contains six different hormone-producing cell types. One of these probably possesses a gonadotrophic function. Degenerative phenomena in the pituitary were found in the sexually ripe and the spent salmon, but only to a limited extent. The implications of the changes in the occurrence of the six different cell types and the degenerative alterations are discussed in relation to gonad development and the death after spawning.

The Sodium, Potassium, and Water Content of the Flesh of Sockeye Salmon (Oncorhynchus nerka) in Relation to Sexual Development and Starvation

The influence of feeding on the changes that occur in the skeletal muscle content of sodium, potassium, and water in sockeye salmon (Oncorhynchus nerka) during sexual development and spawning has been investigated. Feeding has little, if any, effect on the changes. Thus it appears that the period of starvation these fish undergo during their spawning migration under natural conditions is not the major cause of the degeneration of their skeletal muscle, but rather that these changes are associated in some manner with the development of the gonads, presumably through the mediation of hormones.

Effects of Feeding on the Thyroid, Kidney, and Pancreas in Sexually Ripening Adult Sockeye Salmon (Oncorhyncus nerka)

In unfed adult sockeye salmon, Oncorhynchus nerka, histological examination showed extensive degenerative changes in the thyroid, pancreas, and kidney during gonad development. The more pronounced changes were generally noted in starved fish spawned in the wild. Feeding either prevented (thyroid) or distinctly reduced (pancreas, kidney) these changes in the sexually ripe fish. In fed spent sockeye the thyroid showed little change, the kidney exhibited further deterioration although not as marked as in the corresponding unfed fish, but the pancreas showed marked degenerative changes comparable with those exhibited in the unfed.

Post-Spawning Death of Pacific Salmon: Sockeye Salmon (Oncorhynchus nerka) Maturing and Spawning in Captivity

It has been shown that sockeye salmon, Oncorhynchus nerka, will start to eat soon after capture during their freshwater spawning migration. Some will continue to eat up to, during, and after spawning, while others stop eating shortly before spawning. The effect of feeding has been investigated histologically in a number of tissues by comparison of feeding fish, unfed controls, and fish spawned in the wild. Atrophy, and often degeneration of the liver, stomach, and intestine in post-spawned unfed controls and fish spawned in the wild was equally marked, but was absent or much less pronounced in fed fish.

OLFACTORY PERCEPTION IN JUVENILE SALMON: II. CONDITIONED RESPONSE OF JUVENILE SOCKEYE SALMON (ONCORHYNCHUS NERKA) TO LAKE WATERS

Sockeye salmon smolts were conditioned to distinguish between waters from two natural sockeye nursery systems, Great Central Lake (from which the smolts were obtained) and Cultus Lake. The attractant from each water was volatile, but that from Great Central Lake was the more readily volatilized of the two. Volatile material from Great Central Lake water was collected and shown to evoke a response in the group of fish conditioned to whole Great Central Lake water.

Olfactory Perception in Migrating Salmon: III. Stimulants for Adult Sockeye Salmon (Oncorhynchus nerka) in Home Stream Waters

Adult sockeye salmon (Oncorhynchus nerka) captured during their spawning migration to Great Central Lake, British Columbia, show a consistent response in the laboratory to water taken from the outlet of the lake. The specificity of this response has been confirmed and the responses to water from streams feeding Great Central Lake have been determined. A portion at least of the stimulatory material is volatile and can be retained in a cold trap. Concentration of the active factor has been achieved by a freezing-out technique.

2-Phenoxyethanol as a General Anaesthetic for Sockeye Salmon

The dose–response relationship of 2-phenoxyethanol, as a general anaesthetic, in adult sockeye salmon (Oncorhynchus nerka) has been investigated. At 11 °C the effective dose (ED50) and lethal dose (LD50) were approximately 43 and 130 ml/100 Imperial gal, respectively. The therapeutic ratio [Formula: see text] was more than 3, indicating a good margin of safety. At a lowered aquarium temperature of 4 °C the anaesthetic effects of 2-phenoxyethanol were potentiated. ED50 and LD50 at this temperature were approximately 25 and 130 ml/100 gal of water, respectively. The therapeutic ratio was more than 5, indicating that the margin of safety was increased by the decrease in temperature.

Resumption of Feeding by and Survival of Adult Sockeye Salmon (Oncorhynchus nerka) Following Advanced Gonad Development

Adult, migrating, fasting sockeye salmon (Oncorhynchus nerka) were held in captivity in fresh water without spawning well beyond the time when they would normally have done so and died. A few of the fish were then gonadectomized and force feeding was begun. A few unoperated fish were fed similarly while the remainder served as unoperated, unfed controls. The gonads of the operated fish were well developed. After a period of feeding of about four months some fish in each group had survived. The fed fish had regained their green color and much of their weight and vigor, while the surviving unfed fish were extremely emaciated and listless. At this time voluntary feeding by the force-fed fish was observed for the first time, and it was then found that the five surviving unfed controls would also take food voluntarily. While two of these fish died without apparent improvement in their condition, the other three gradually regained green color, weight and vigor.

Olfactory Perception in Juvenile Salmon.: I. Observations on Response of Juvenile Sockeye to Extracts of Foods

The introduction of aqueous extracts of natural foods into an aquarium holding juvenile sockeye evoked exploratory and feeding responses in fish that had previously eaten the foods, but failed to do so in fish that had not. Responses were characterized by breaking up of the school, increased swimming speeds, and the swimming of the fish into lighted areas. The fish detected concentrations of the active substance(s) in the order of one part in 80,000,000, based on the wet weight of the whole food.

OLFACTORY PERCEPTION IN MIGRATING SALMON: II. STUDIES ON A LABORATORY BIO-ASSAY FOR HOMESTREAM WATER AND MAMMALIAN REPELLENT

A laboratory bio-assay, based on the response of adult migrating sockeye salmon (Oncorhynchus nerka) to homestream water, is described. A characteristic response to the repellent in mammalian skin is discussed. The homestream substance(s) was tentatively identified as volatile, dialyzable, neutral, and heat-labile.The transportation and holding of sockeye in captivity was investigated.

The Liquefaction of British Columbia Herring by Ensilage, Proteolytic Enzymes and Acid Hydrolysis

Nearly all the herring landed on the British Columbia coast during the past 10 years has been converted by the wet reduction process to animal feed, the bulk of which was in the dry form. While the final products of the wet reduction process have proven to be of a high nutritive value, in the dry form they have the disadvantage in the amount of handling required during transit. A liquid product would not only reduce handling costs but also it would act as a binder in otherwise dry feed rations.Three methods have been tested to liquefy the whole herring: ensilage, high pressure steam liquefaction and proteolytic enzyme solubilization. In the ensilage process the liquefaction of the whole fish in an acid medium was achieved in 72 hours at 37 °C. The liquefaction of the fish was shown to be due to proteolysis by the natural occurring enzymes present both in the viscera and in the flesh of the fish and was not caused by the action of bacteria. While up to 70% of the whole fish was solubilized by autoclaving the fish in an acid medium, the resulting free oil was high in free fatty acid content and the liquid concentrate dark in colour. Of the commercial proteolytic enzymes tested, pepsin achieved the highest maximum solubilization, followed by bromelin and Rhozyme B-6. An oil–protein emulsion stable at 100 °C and to salting, however, was formed in the digest of each enzyme tested.Liquid fish products were prepared under pilot-plant conditions for future nutritional assay.

Seasonal Variation in the Collagen Content of Pacific Herring Tissues

The total amount of collagen and its relative solubility was determined in 3-year-old herring of the same population caught at two periods, June and January, representing two extremes of the sexual cycle. Sexually mature herring, caught in January, contained 40% more collagen than sexually immature fish caught in June. When fractionated into neutral salt-soluble, acid-soluble and insoluble collagen, the proportions of the three fractions remained much the same at both seasons of the year. When various tissue fractions of the fish were examined at the two seasons it was found that not only did the concentration of collagen change in the tissues with maturation but the contribution which some of the tissues made to the total body weight also changed. The skin + scales fraction contributed most to the increase in collagen in February herring. This was due partly to a higher concentration of collagen in these tissues at this season and partly to the higher proportion of skin + scales at this time of year. The significance of these findings in relation to the biochemistry of sexual maturation is considered.