New observations about the fertilisation capacity and latency time of sperm inseminated into the ovary of African catfish (Clarias gariepinus), an oviparous modelfish

Abstract

In our former study, we proved that sperm injected into the ovary by catheter through the oviduct 10-12 h before hormonally induced ovulation, retains its fertilizing capacity for several hours. Using this method, we produced viable larvae via in vitro fertilisation. The aim of this study was to investigate the time-dependent fertilizing capacity of sperm which were introduced into ovary. Sperm samples (2 mL sperm / bodyweight kg) were incubated in gonad lobes 5, 10, 15, 20, 25, 36 and 48 h before the gamete stripping. Ovulation was induced by extracted carp pituitary (CPE) hormonal administration (5 mg CPE / BW kg). There were no statistical differences (p < 0.05) among the hatching rates in the 5-25 h treatment groups, but we observed large individual fluctuations in fertilisation and hatching rate within the groups. However, at 48 h the treated group showed low fertilisation and hatching rate indicating loss of fertilizing capacity. In our second experiment cycle, three different inseminated sperm dosages were tested on fertilisation from the same pooled sperm batch; 2 mL, 1 mL and 0.5 mL sperm volume / BW kg. The 0.5 mL sperm dosage showed statistically (p < 0.05) higher fertilisation and hatching rate indicating that small milt volume was enough to apply for propagation. According to scanning electron microscopic analysis, this is the first observation that there is a chance for ‘internal gametic association’ reproduction strategy in fish species, where there is no direct contact between the two sexes in the spawning.