HCG-induced spawning of the catfish, Clarias macrocephalus (Gunther)

Ovulation was induced in catfish, Clarias macrocephalus (Gunther), with vitellogenic oocytes of at least 1050 μm in diameter by using various dosages of either human chorionic gonadotropin (HCG, 1–5 I.U./g body wt.) or homoplastic pituitary extract (PE, if 3.5–7.0 mg 100 g body wt. ) given as a single intramuscular injection. At ambient water temperature (26–31°C), ovulation occurred within 13–18 h post-injection. HCG at a dose of 2 I.U./g body wt. induced ovulation in 95% of the fish tested. This is the minimal recommended dose and it is effective irrespective of the time of day that the injection is administered. In contrast, ovulation was induced in 88% of fish treated with PE at 3.5 mg 100 g body wt. Following HCG administration, the mean egg diameter at ovulation was 1458 ± 12 μm compared with 1196 ± 31 μm prior to treatment, showing an increase of 22%. HCG is therefore an effective substitute for fish pituitary gonadotropin in the induction of ovulation of C. macrocephalus. The hatching rate of ovulated eggs fertilized artificially with milt obtained from the testes of a freshly-killed fish was consistently similar for both PE- and HCG-treated fish. For fish treated with 2 I.U. HCG/g body wt., the mean hatching rate was 72.3 ± 1.6% while that for PE-treated fish ( 3.5 mg 100 g body wt. ) was 73.3 ± 3.8%.