Gonadal Development, Fecundity and Spawning Pattern of Synodontis Schall (Pisces: Mochokidae) From Jamieson River, Nigeria.
The paper examines aspects of the reproductive biology of Synodontis schall from Jamieson River, Nigeria with emphasis on the histology of the gonads. Sampling was carried out between October 2010 and October 2011 and 623 specimens of Synodontis schall were collected using cast and gill nets. In the laboratory, specimens were measured for total length (cm), standard length (cm), weighed (g) and dissected. Standard techniques for sex ratio, gonadal maturation, size frequency distribution of ovarian oocytes and fecundity were used in analysis. Linear regression technique was used to determine the relationship between fecundity and fish length, body weight and ovary weight. The gonads were observed for morphological and histological changes, and the results used to classify their different developmental stages and maturity into five successive stages-Immature, Recovery, Maturing, Ripe and Spawning. The total lengths of ripe specimens range from 19.40cm to 26.20cm with body weights of 73.62gm to 252.15gm and ovary weights of 2.30gm to 28.41gm. Absolute fecundity ranged from 1530 to 13,965 eggs with a mean of 6080 eggs. Gonadosomatic index (GSI) increased with increase in the stage of gonad development for each sex. GSI values were lower in males than females of corresponding stage of development. Fecundity-body weight and fecundity-ovary weight logarithmic relationships were more highly correlated and significant than the fecundity-total length relationship. There is evidence that the female spawns once annually. Results of the above investigation will ensure the conservation of S. schall in Jamieson River, as well as its full utilization as a sustainable resource.
Oboh IP, Ogbeibu AE and Ogoanah SO