William S. Hoar

Smolt Transformation: Evolution, Behavior, and Physiology

Literature concerned with the appearance of smolts (silvery color, streamlined body form), their physiology (salinity relationships, endocrinology), and their behavior (territorial and schooling) i...

Hormones and the reproductive behaviour of the male three-spined stickleback (Gasterosteus aculeatus)

Male sticklebacks (Gasterosteus aculeatus), castrated in the pre-nest building phase, show a high level of aggressive behaviour if they are maintained under a long photoperiod day—16 hours illumination alternating with 8 hours of darkness. Castrates under short photoperiods, with only 8 hours illumination per day, are much less aggressive. Pituitary gonadotropic activity is assumed to be high in the long photoperiod fish and low in the short photoperiod groups. If castrated in the nest building phase, all nest building and associated reproductive activities cease. Methyl testosterone initiates full development of secondary sex characters in castrates under either photoperiod regime but agonistic behaviour and nest building is less likely to be seen and is of lower intensity in groups maintained under the short photoperiods. Neither methyl testosterone nor the mammalian gonadotropins (FSH, LH, PMS, HCG) will regularly induce full development of reproductive behaviour in unoperated fish maintained continuously under short photoperiods. It is indicated that the gonadal androgen alone is responsible for the secondary sex characters. It is also essential to the development of nest building behaviour but the complete expression of nest building and associated reproductive behaviour requires an interaction of gonadal and hormones.

The effects of prolactin and testosterone on the parental behaviour of the male stickleback Gasterosteus aculeatus

Abstract Injections of mammalian prolactin (lactotrophic hormone LTH) failed to induce fanning behaviour or to intensify either displacement fanning or parental fanning of the male threespine stickleback. Castration greatly reduces or entirely eliminates fanning behaviour in sexually active male sticklebacks. Treatment with methyl testosterone maintains or restores fanning in castrated males. With a series of graded doses of methyl testosterone, the earlier stages of reproductive behaviour (sand digging) appear at the lower dosages while the later elements (fanning) are evident at full intensity only with the higher dosages. All of the evidence indicates that the parental fanning is regulated by the androgenic hormones of the testes. Prolactin probably exerts its physiological action during the pre-sexual migratory period of the reproductive cycle.

Inhibition of the pituitary gonadotropic activity of fishes by a dithiocarbamoylhydrazine derivative (I.C.I. 33,828)

Abstract Three teleost fishes, Carassius auratus, Gasterosteus aculeatus , and Cymatogaster aggregatus , have been injected for periods of about 4 weeks with a suspension of Methallibure (I.C.I. Compound 33,828). Although division of the primary germ cells continued, the gametogenetic processes of maturation were suspended in the gonads of both sexes of all three species. The brush border segments of the kidney tubules of Gasterosteus , a secondary sex character which increase in thickness under the influence of male gonadal hormones, remained in a state characteristic of immature fish; control animals showed changes characteristic of the breeding season. It is concluded that this compound blocks the action of pituitary gonadotropins on both the gametogenetic and the endocrine tissues of the testis.

SOME EFFECTS OF ULTRAVIOLET RADIATION ON SOCKEYE SALMON EGGS AND ALEVINS

Ultraviolet radiation of wave lengths from 2800 A to 3100 A, generated by a General Electric RS sun lamp, was used to irradiate eggs and alevins of the sockeye salmon (Oncorhynchus nerka). Mortality curves are presented for a series of measured dosages. Irradiation of eggs in the later stages of development produced a stimulating effect on the rate of hatching. These premature alevins, which hatched a month before the controls, were abnormal in several respects. The vertebral column was curved downward over the region of the heart, growth was retarded, the yolk was not utilized as rapidly as in the controls and pigmentation was delayed. The mortality was particularly high at the time of hatching and the process was abnormal. Histological examination of irradiated alevins revealed changes in the epidermis and fibroelastic layers of the skin. These were localized to the irradiated regions. Heavy doses produced severe degeneration of the epidermal layer with the formation of granules in the nuclei, the break...

Effects of Temperature On the Responses of Young Salmon To Water Currents

The rheotactic responses of three species of juvenile Pacific salmon (genus Oncorhynchus) were studied under varying temperature conditions. Rheotaxis is predominantly positive at lower temperatures but frequently becomes actively negative at higher temperatures. A positive response was usual at temperatures which normally prevail during the seaward migration of these fish. The presence or absence of shelter may markedly modify rheotactic responses. If exposed to light young salmon may show a negative rheotaxis while a positive response occurs if shelter is available.