Abstract
This study was conducted to evaluate some aspects of the reproductive biology of the African Bonytongue Heterotis niloticus from the Great Kwa River, Cross River State Nigeria with the view to encourage conservation and rational measures for sustainable management of the species. A total of 62 matured H. niloticus were sampled and their gonadosomatic index (GSI), hepatosomatic index (HSI), condition factor, fecundity and egg diameter (mm) were studied in other to determine the spawning season of the fish. Gonadosomatic index and hepatosomatic index showed an inverse relationship during spawning seasons. Total length (TL-cm) ranged between 47.1 cm – 76.2 cm and total weight (TW – g) ranged between 4300g - 1169g with sex ratio of 1:1.2 (male: female) revealing a dominant female population. Fecundity ranged from 511 oocytes (48.4cm TL; 1.69 kg wt, 5.9g gonad weight) to 7822 oocytes (69.3cm TL, 3.11kg wt. 14.9g gonad weight). The regression equation derived from the scattered diagram in the relationship between fecundity and total weight, total length gonadosomatic index and length-weight is; F= 6.6231TW0.837, R2= 0.2456; F= 5.1112TL1.6367, R2= 0.1606; F= 10680GSI0.9276, R2= 0.6567; TW= 0.4072TL2.0987, R2= 0.7533, the relationship were significant (p < 0.05). Fecundity and ovary weight relationship showed a positive correlation coefficient of 1. The highest egg diameter (0.92±0.01) was recorded in May and other months with corresponding high gonadosomatic index performance to confirm spawning period. In view to encourage conservation by investigating measures for sustainable management of the species, this study observed that H. niloticus spawns throughout the year.
 Ikot, N. U. | Department of Zoology and Environmental Biology, University of Calabar, P.M.B.1115 Calabar, Nigeria
Highlights
The Great Kwa River in recent times has witness a significant increase in human activities which had traditionally centred on artisanal fisheries, aquaculture and small-scale farming along the coastal regions
A total of 62 H. niloticus were sampled from Great Kwa River from January to December
Total length (TL) of all the samples examined ranged from 47.1cm to 76.1cm while the total weight (TW) ranged from 1056g to 3809g
Summary
The Great Kwa River in recent times has witness a significant increase in human activities which had traditionally centred on artisanal fisheries, aquaculture and small-scale farming along the coastal regions. Agricultural farms are the primary engagement witnessed at the coastal regions of the Great Kwa River. The surrounding mangrove vegetations have suffered human interferences resulting in breeding ground and habitat loss, degradation and undoubtedly many fish species including Heterotis niloticus are threatened and endangered Mustapha (2010). Due to general environmental degradation which includes oil spillages, pollution and destruction of mangrove swamps, this species has lost an estimated 60% of its previous breeding and nursery habitat in Nigeria with subsequent reduction in populations (Bake & Sadiku, 2005; Offem et al, 2011). The size and flesh of this fish species attracts fishers, aquaculturist and consumers
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