The African catfish, Clarias gariepinus, a model for the study of reproductive endocrinology in teleosts

Abstract

In their natural habitat African catfish, Clarias gariepinus, show a discontinuous reproductive cycle. This cycle follows changes in the gonadotropic activity of the pituitary. Gonadotropin release has been shown to be under dual hypothalamic control, i.e. a gonadotropin-releasing hormone ( GnRH) and a gonadotropin release-inhibiting factor (GRIF) , which turned out to be dopamine.Gonadal sex hormones influence gonadotropin release by a negative feedback, and a model has been developed to explain their mode of action.Steroid formation has been studied in testes, seminal vesicles and ovaries and correlated with the annual reproductive cycle. Steroid glucuronides, originating from the seminal vesicle, act as male sex pheromones; ovulation seems to be synchronized by female pheromones.Techniques for the induction of ovulation were developed. Only brood&h, reared from eggs to maturity under favourable conditions, show a continuous reproductive cycle and can be induced to produce viable eggs throughout the year.

Exploration of natural cryoprotectants for cryopreservation of African catfish, Clarias gariepinus, Burchell 1822 (Pisces: Clariidae) spermatozoa

“…In the wild, it has a discontinuous annual reproductive cycle (Van Oordt and Goos 1987) and the breeding season correlates with periods of maximal rainfall . Outside this range of breeding seasons, the availability of high quality broodstocks is scarce, as in general the quality and quantity of spermatozoa decreased as the spawning season progressed (Moczarski and Koldras 1982;Fauvel et al 1999;Suquet et al 2000).…”

In vivo activity of native GnRHs and their analogues on ovulation in the African catfish, Clarias gariepinus (Burchell)

“…The ovaries of such females show a continuous cycle with numerous postvitellogenic oocytes throughout the year. These females can be used for artificial propagation at all seasons and ensure the production of large quantities of viable eggs all year round (Van Oordt & Goos 1987). Therefore, we could set up our experiments disregarding the time of the year.…”

“…The animals were fed with dry pellets (protein content: 48%) at a ration of 1.0% of body weight (BW). Experiments were performed with sexually mature female fish, 13–16 months of age and with a BW of 700–1200 g. In African catfish, both raised and constantly kept under favourable husbandry conditions, the ovary shows a continuous cycle with postvitellogenic oocytes at all seasons, but without spontaneous oocyte maturation and ovulation (Van Oordt & Goos 1987). One week before each experiment, the fish were transported to the hatchery of Szarvas Fish and placed in polypropylene tanks with running well water.…”

Effects of exogenous neurohormone, gonadotropin (GtH) and dopaminergic drugs on the serum GtH content and ovulatory responsiveness of wild catfish, Silurus asotus (Linnaeus, 1758)

“…This involves intraperitoneal or intramuscular injection of a superactive analogue of GnRH, specifically salmon [ d ‐Arg 6 , Pro 9 ‐NET]‐GnRH (sGnRH‐A) or [ d ‐Ala 6 , Pro 9 Net]‐luteinizing hormone‐releasing hormone (LHRH‐A), with a DA receptor antagonist, specifically pimozide (PIM) or domperidone (DOM), to remove the inhibitory influence of DA on pituitary GtH secretion (Peter, Lin & Van Der Kraak 1988; Lin, Zhou, Van Der Kraak & Peter 1991). This combination well stimulated the normal ovulatory surge of GtH in goldfish Carassius auratus (Linnaeus, 1758) (Chang & Peter 1983; Sokolowska, Peter & Nahorniak 1985a; Sokolowska, Peter, Nahorniak & Chang 1985b) and common carp Cyprinus carpio (Linnaeus, 1758) (Lin, Van Der Krrak, Zhou, Liang, Peter, Rivier & Vale 1988; Peter et al 1988), Chinese loach Paramisgurnus dabryanus (Sauvage, 1878) (Lin, Peng, Lu, Zhou, Van Der Kraa & Peter 1985; Lin, Peng, Van Der Kraak, Peter & Breton 1986; Lin et al 1988; Lin et al 1991), African catfish Clarias gariepinus (Burchell, 1822) (De Leeuw, Resink, Rooyakkers & Goos 1985; Goos, Joy, De Leeuw, Van Oordt, Van Delft & Gielen 1987; Van Oordt & Goos 1987) and coho salmon Oncorhynchus kisutch (Walbaum, 1792) (Van Der Kraak, Donadson & Chang 1986). This method of using a GnRH‐A or LHRH‐A with DA antagonist PIM or DOM for inducing ovulation of cultured fish had been termed the Linpe technique (Peter et al 1988).…”