Effects of 17α-methyltestosterone on seminal vesicle development and semen release response in the African catfish, Clarias gariepinus

The African catfish, Clarias gariepinus (formerly C. lazera; Fishelson et al., 1994), is well adapted to captivity, and under conditions of 258C and 12 h light per day, the pituitary gland stores large amounts of gonadotrophin and shows a limited continuous secretion of this hormone. The amount of gonadotrophin is sufficient for sustained gametogenesis and gonadal steroid production, but not for spontaneous semen release and male reproductive behaviour (van Oordt et al., 1987). For artificial reproduction, male catfish are killed, their testes removed and macerated, and intratesticular semen is spread over the eggs. In a previous study on African catfish (A. T. M. Viveiros and J. Komen, unpublished), the effects of drugs that are known to increase plasma gonadotrophin concentrations were evaluated on spermiogenesis and semen release response by abdominal massage. The study tested both exogenous gonadotrophin, by injecting males with Clarias or carp pituitary suspensions (cPS), and endogenous gonadotrophin, by stimulating fish pituitary with LH releasing hormone analogue (LHRHa), LHRHa plus a dopamine antagonist or ovaprim (salmon GnRH analogue plus a dopamine antagonist). Spermiogenesis, assessed by intratesticular semen volume and sperm concentration, was improved only after two consecutive injections of cPS. Stripping of a few drops of fluid with some viable spermatozoa was possible after two consecutive injections of cPS or after combinations of cPS followed by ovaprim injections. Semen volume, spermatocrit and sperm concentration were lower in the stripped fluid than in the intratesticular semen from the same group of males. Similar inconclusive results on the semen release response and sperm production after maturational hormone treatment were described for Asian catfish, C. macrocephalus (Tan Fermin et al., 1999), Asian green catfish, Mystus nemurus (U. Schneiderat, personal communication) and Blue catfish, Ictalurus furcatus (Dunham, 1993). Collectively, these results indicate that male catfish kept in captivity cannot be stripped of semen for reasons other than the lack of a gonadotrophin surge. Several reports have indicated that stripping of semen from catfishes is difficult because the testes are located deep within the body cavity and are covered by other organs (for example, gut and stomach). Therefore, during stripping, most of the pressure applied to the abdomen is on the other organs. In addition, the ripe milt gathers along the convex lobular edge of the testes rather than passing through the Effects of 17α-methyltestosterone on seminal vesicle development and semen release response in the African catfish, Clarias gariepinus