ASPECT OF REPRODUCTIVE BIOLOGY OF PARACHANNA OBSCURA, GUNTHER 1861 IN A SOUTHWESTERN NIGERIAN RESERVOIR

摘要

African snakehead (Parachanna obscura) is a highly valued freshwater fish species in Nigeria, but its availability for economic and nutritional benefits is being threatened as a result of overdependence on wild source. Effort at bringing it to culture is, however, being limited by paucity of information on its biology among other challenges. Therefore, key aspects of the reproductive biology of this species were investigated as a prelude to artificially propagate it. 688 live samples comprise of 394 females (12.6-45.0cm TL) and 294 males (12.8-41.6cm TL) were fortnightly obtained in Eleyele Lake between November 2014 and October 2016 from fishermen majorly using longline, cast nets and gillnets of various mesh sizes. Morphometric parameters of fish were taken, and each sample dissected for sex identification following standard method. The maturation stages were analysed using macroscopic and standard histological techniques. The sex ratio of samples varied significantly (p<0.05), with 1.34 females for every male. Five stages of oogenesis and three stages of spermatogenesis were obtained from samples analysed. Mean gonadosomatic index were significantly higher in May (2.26±0.86%), June (2.08±0.80%) and January (1.98±0.77%) for female samples and in June (0.18±0.06%) and December (0.21±0.06%) for male, implying peaks of gonadal development for the sexes. Length at first maturity calculated was 26.6 cm for males and 25.8 cm for females. The diameter of ova, however, varies from 0.60 to 1.42 mm. Absolute fecundity ranged between 336 (at 20.5cm total length) and 7,033 (at 36.7 cm total length). The relationship between fecundity and total length, weight, ovary length and ovary weight was linear and positive. This research provides key information necessary for artificial propagation of P. obscura.