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A study of the effects of prolactin and testosterone on the parental behaviour of the male stickleback Gasterosteus aculeatus L. Smith, Reginald Jan Frederick

Abstract

Male stickleback did not show a greater increase in displacement or parental fanning when injected with prolactin than they did when injected with saline solvent alone. Displacement fanning was higher in gonadectomized fish with pituitary activity suppressed by short photoperiod than in gonadectomized fish with an active pituitary under long photoperiods when both groups were treated with the same testosterone concentration. Injection of pituitary fractions into the short photoperiod fish reduced fanning to the levels found under long photoperiods. Normal males under long photoperiod showed significantly higher fanning than any of the gonadectomized groups indicating that methyl testosterone in concentrations used did not fully replace the effects of the normal gonad. Exposure of males to a wide range of testosterone concentrations indicated that a relatively high concentration of testosterone was required for normal fanning. Low levels of fanning occurred after gonadectomy of fish in breeding condition in both "displacement" fanning and parental fanning stages, indicating the gonad was not required for performance of the fanning pattern as such but was required for fanning to reach levels approaching these found in normal fish. No evidence was found that prolactin initiates or maintains the parental fanning cycle. Testosterone however was necessary for normal fanning levels.

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