would most likely occur in species where males with ripe gonads are con-
tinuously available waiting for new females to encounter their nests. Al-
though very interesting, these experiments concerning S. mossam bicus should
be performed on other species, and efforts should be made to look for the
existence of pheromone-like substances which have been shown in other fish
(Solomon 1977).
The Role of Internal Factors in the Regulation
of Reproductive ActivityNumerous organs, endocrine glands, and hormones are involved, directly
or indirectly, in the regulation of reproduction in fish as in other vertebrates
(Fontaine 1976; Olivereau 1977). This complex control system is directed
by the nervous system which integrates external stimuli together with
ontogenetic and physiological constraints, and exerts its control mainly
through the hypothalamo-pituitary-gonad axis. The following section will
deal essentially with the functional modalities of this axis. Points which are
still very controversial in other teleosts, and which have not even been
studied in cichlids to our knowledge will be omitted: for example, the role
of the pineal organ.THE ROLE OF THE PITUITARYMany works reviewed by Pickford and Atz (1957) have demonstrated how
important the role of the pituitary is in the control of reproduction in fish.
This role was confirmed in cichlids (Sarotherodon spilurus) by means of
chemical hypophysectomy using methallibure and replacement therapy
(Hyder 1972; Hyder et al. 1974; Hyder et al. 1979). Methallibure, which was
shown to inhibit gonadotropin secretion by the pituitary in fish (Breton et
al. 1973) as it is known to do in mammals, induces an effective gonadal
regression in both male and females. spilurus after 4 to 5 weeks of treatment
with daily doses of 1 mg/l of aquarium water (Hyder 1972). This treatment
results in an extensive resorption of yolk-laden oocytes and a complete
inhibition of vitellogenesis in females and in the complete inhibition of two
steps of spermatogenesis in males: the step between spermatogonia and
spermatocytes (meiosis) and final spermiation. A similar effect was con-
firmed by Lanzing (1978).
The present state of knowledge of teleost fish reproduction tends to
support the hypothesis that two different pituitary gonadotropins are
involved in the control of gametogenesis. One purified at first from carp,
Cyprinus carpio (Burzawa-Gerard 1971), trout, Salmo gairdneri (Breton
et al. 1976) and in salmon of the genus Oncorhynchus (Donaldson et al.
1972) is characterized by its control over final intrafollicular oocyte matura-
tion (Jalabert et al. 1974) and its effect upon spermatogenesis (Billard et al.
1970). A second kind of gonadotropin which seems necessary for vitello-
genesis was recently purified from carp and salmon pituitaries (Idler and Bun
Ng 1979).