EFFECT OF VARYING LATENCY PERIOD ON THE QUANTITY AND QUALITY OF OVA AFTER HCG-INDUCED OVULATION IN THE AFRICAN CATFISH, HETEROBRANCHUS-LONGIFILIS (TELEOSTEI, CLARIIDAE)

In captive Heterobranchus longifilis females, oocytes maturation and o vulation are induced by a single injection of human chorionic gonadotr opin (hCG) at a dose of 1.5 I.U./g body weight. In the present study, three experiments were performed in order to specify the timing of ovu lation and the effects of varying latency period on the quantity and q uality of the collected ova. The ova quality was estimated by hatching percentage and proportion of deformed larvae obtained after artificia l fertilization. The results showed that, in an individual female, ovu lation of postvitellogenic oocytes is not synchronous and takes 3 to 4 hours to be completed, between 7-8 h and 11 h after hCG injection at 30 degrees C. The quantity of ova that could be collected by handstrip ping increased with the latency period, from 18000+/-12000 to 72000+/- 29000 ova per female at 8 h and 11 h after injection, respectively. H owever, the first ova obtained (8 h after injection) were of good qual ity (94% hatching) and showed no signs of incomplete final maturation. Eleven hours after injection, the percentages of ovulated oocytes wit hin the whole ovarian population of postvitellogenic oocytes were high in all the females, being generally around 90%. After ovulation, agin g of ova occurred rapidly: the proportion of deformed larvae increased significantly (from 4 to 20%) 2 h after completion of ovulation and, 4 h post-ovulation, hatching percentage dropped from 92 to 36%. In H. longifilis, the optimal latency period can be defined as the time, fro m injection to stripping, allowing the best compromise between quantit y and quality of ova released. This latency period was found to be 11 h following hCG injection at 30 degrees C, and corresponds approximate ly to the completion of ovulation.