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Regulation of spawning behaviour in the female goldfish, Carassius Auratus

University of British Columbia

This study of the regulation of spawning behaviour in the female goldfish (Carassius auratus) identified four endogenous factors believed to play major roles in spawning behaviour: (i) stimuli from ovulated eggs, (ii) ovarian steroids, (iii) pituitary hormones, and (iv) prostaglandins. Spawning behaviour is synchronized with ovulation by the stimulus of an intraovarian mass of ovulated eggs. Normally, female goldfish begin to spawn on the morning of the day of ovulation and perform as many as several hundred spawning acts over a period of several hours; spawning behaviour ceases when all ovulated eggs have been shed. The duration of spawning behaviour was extended if oviposition (the release of eggs through the ovipore) was prevented by placing a plug in the ovipore. Spawning behaviour was terminated when ovulated eggs were removed by hand-stripping and restored when ovulated eggs were injected through the ovipore and into the ovarian lumen. This effect of eggs on spawning behaviour was not restricted to the day of ovulation but was seen in all fish with ovaries in any stage of vitellogenesis. Injection of several substitutes for ovulated eggs induced low levels of spawning behaviour. Injection of ovulated eggs failed to induce spawning behaviour in female goldfish with regressed, nonvitellogenic ovaries. Pretreatment with a variety of gonadal steroids restored the spawning response to egg injection in these intact, regressed fish. Hypophysectomized fish did not perform spawning behaviour when injected with ovulated eggs. Pretreatment of hypophysectomized fish with homogenized goldfish pituitaries or partially purified salmon gonadotropin (SG-G100) restored the response to egg injection. Aminoglutethimide, an inhibitor of steroid synthesis, blocked the effect of SG-G100 on spawning behaviour, suggesting gonadotropin may exert its effect on behaviour by stimulating steroidogenesis. However, steroid treatments were totally ineffective in restoring the response to egg injection in hypophysectomized fish. Prostaglandin (PG) appears to be involved in mediating the behavioural response to ovulated eggs. Indomethacin (IM), an inhibitor of PG synthesis, blocked the onset of spawning behaviour following egg injection. Injection of PGF₂ restored spawning behaviour in egg-injected, IM-treated fish; PGE₂ was less effective and PGE₁ was without effect. Injection of PGF₂ induced normal spawning behaviour in fish which had not been injected with ovulated eggs, suggesting that ovulated eggs induce spawning behaviour by stimulating synthesis of PG. The effects of PG on spawning behaviour of hypophysectomized fish treated with SG-G100 or steroids paralleled the effects of egg injection on fish receiving similar treatments; SG-G100 restored the spawning response to injection of PG, while steroid treatments were without effect. Mechanisms by which ovarian and pituitary hormones and prostaglandins may influence spawning behaviour are discussed and a model of the regulation of spawning behaviour is proposed. In addition, an attempt is made to provide a theoretical basis for comparing the regulation of sexual behaviour in female vertebrates.

Text

2010-02-21

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http://hdl.handle.net/2429/20713

Zoology

University of British Columbia

Graduate