A Study of the Reproductive Biology of the Catfish, Chrysichthys Nigrodigitatus (Lacepede) in Nigeria.
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Ezenwa, Benard. J.O.
University of Lagos
The catfish, Chrysichthys nigrodigitatus (Lacépède) is widely distributed in Nigeria. Because of its growing importance in fish-farming and its abundance in both fresh and brackish water in Nigeria, some aspects of its reproductive biology were investigated in some details. The study lasted 27 months from October 1978 to December 1980. The monthly histological development and seasonal changes of the ovary and testis were examined. The process of oogenesis was made up of six stages in agreement with the maturity scale of Nikolsky (1963a): stage 1 (immature): consists of very small and spherical oocytes; stage 2 (Resting): shows very slight increases in diameter of oocytes; stage 3 (Naturation): marks the beginning of yolk deposition; stage 4 (almost mature): characterized by abundant yolk materials which fill the oocytes; stage 5 (spawning): egg membranes rupture and allow eggs to lie free in the lumen; stage 6 (spent condition) : consists of ovaries which look like empty sacks. The annual reproductive cycle in the female is divided into five histologically distinct periods: - pre-spawning (October – November) ; Spawning (December – January) ; Post-spawning (February -, March, April); resting (May, June); Maturing (July, August, September). Spermatogenesis was described in five stages: stage 1 Spermatogonia; stage 2: Spermatocytes; stage 3: Spermatids; stage 4: Spermatozoa; stage 5; spent condition. As in the female, there are five periods in the annual reproductive cycle of the male: Pre-Spawning (October to November); Spawning (December to January); Post-Spawning (February, March, April); resting (May, June); Maturing (July, August, September). The spawning habits were investigated. Sexually mature individuals were found only during December thus suggesting that the species breeds only once a year. Sexual maturity in the females was attained when the fish was between 29cm – 32cm total length, while in the males the range was between 30cm – 35cm total length. There were more females than males during the spawning season. Experiments in glass aquaria and concrete tanks confirm that there is pairing behaviour and that spawning could take place in dark hollow cavities with either sandy or muddy bottoms. The monthly examination of Physico-chemical parameters of Badagry lagoon helped to throw more light on the water environment during spawning.
Fish-farming , Reproduction , Reproductive Biology , Reproductive cycle , Spawning
Ezenwa, B. J. O. (1981). A Study of the Reproductive Biology of the Catfish, Chrysichthys Nigrodigitatus (Lacepede) in Nigeria. A Thesis Submitted for the Degree of Philosophy of the University of Lagos, Nigeria.