The Biology and Culture of Tilapias

In cichlids, some attempts have been made to purify and characterize
pituitary gonadotropins. Farmer and Papkoff (1977) obtained two prepa-
rations from S. mossambicus which exhibited some biochemical character-
istics similar to luteinizing hormone (LH) and follicular stimulating hormone
(FSH) from higher vertebrates. The first preparation stimulated testosterone
production in isolated rat testis Leydig cells, an assay which is considered
highly sensitive and specific for mammalian LH. Neither of the two prepara-
tions was assayed for its activity on Sarotherodon gonads. More recently,
Hyder et al. (1979) observed enhanced gonadotropic activity (as judged by
testis stimulation in methallibure-treated S. spilurus) after chromatographic
separation of a glycoprotein hction from S. niloticus. The fraction was the
same as that known to contain FSH when the same biochemical procedure is
applied to pituitary preparations from higher vertebrates. Results are thus
still confusing, and more work remains to be done in order to find specific
bioassays for the gonadotropins of cichlids.
Another pituitary hormone, characterized as a "prolactin-like" hormone,
is believed to play an interesting role in the reproductive physiology of
cichlids, in relation to the regulation of breeding activity and parental care
Bliim and Fiedler (1964) found that injection of ovine prolactin induced
behavioral and histiotropic effects in Symphysodon aequifasciata axelrodi.
The behavioral reactions were of fanning movements with the pectoral fins
orientated to a distinct reference point (normally associated with parental
care towards the brood) and suppression of feeding and fighting tendencies.
The histiotropic effect was an increase in mucous cell production on the
body surface which normally serves to nourish the young in that species
(Hildemann 1959), thus exhibiting a curious analogy with the secretion of
crop-milk in pigeons and milk production in mammals.
In other cichlids, e.g., Pterophyllum scalare, Aequidens latifrons, Cich-
lasoma severum and Astronotus ocellatus (Bliirn and Fiedler 1965) ovine
prolactin induces similar effects, including increase in mucous cell production
although to a lesser extent than in Symphysodon and here this is not related
to nursing of the young in that species. It is possible that mucus secretion
can be related to the osmoregulatory properties of prolactin in fish (Bliirn
1973; Bern 1975). Isolation and purification of Sarotherodon prolactin was
successively reported by Bliim (1973) using behavioral and histiotropic
effects in Symphysodon and by Farmer et al. (1977) using specific assays for
osmoregulation. Considering the pleiotropic action of prolactin, isolating the
same molecule through different kinds of bioassays is not surprising, but a
comparison of different preparations using the same tests would be of
interest in assessing the reality of this pleiotropic role for the same hormone.
Among the alleged multiple actions of prolactin in fish, one could be of
interest for Tilapia and Sarotherodon culture if its mechanism could be
elucidated: the inhibition of gonad development (Bliim 1976). In natural
conditions, gonadal development after spawning might be inhibited during
parental care, which is precisely the period when prolactin is supposed to be
acting. In addition, some antagonism between prolactin and gonadotropins
was found to occur regarding spawning behavior (Bliim and Fiedler 1966).