Growth and reproduction of two Chrysichthys species (Siluriforms, Bagridae), C. nigrodigitatus and C. auratus, in lake Nokoué and Porto-Novo Lagoon (Benin)
Laleye, Ph.; Philippart, J.C. (1993). Growth and reproduction of two Chrysichthys species (Siluriforms, Bagridae), C. nigrodigitatus and C. auratus, in lake Nokoué and Porto-Novo Lagoon (Benin). Belg. J. Zool. 123(Suppl. 1): 40-41
In: Belgian Journal of Zoology. Koninklijke Belgische Vereniging voor Dierkunde = Société royale zoologique de Belgique: Gent. ISSN 0777-6276; e-ISSN 2295-0451, meer
In 1990-1991, Chrysichthys (C. nigrodigitatus and C. auratus) were sampled (nets and traps) in the Lake Nokoue - Porto Novo Lagoon complex (180 km2) in Southern Benin (Western Africa). The age of fishes was determined by the means of periodic marks on transversal cuts of the spiny ray of the dorsal fin. The comparative study of age, size, growth and reproduction in the two species reveals that C. nigrodigitatus grows much faster than C. auratus (total length at 3 years of age, L3 = 20 and 16 cm, respectively) and reaches larger size and weight (maximum observed total lengths-weights= 69 cm - 3.670 g and 40 cm - 527 g; maximum total lengths expected from Von Bertalanffy models L = 93 cm and 40 cm, respectively). C. auratus reaches sexual maturity at 8 cm (minimum size) - 13 cm (100 % mature fishes), corresponding to 2-3 years while the corresponding values are 24-35 cm and 4-7 years in C. nigrodigitatus. The relative fecundity (number of ova / kg of fresh body weight) is higher in C. auratus than in C. nigrodigitatus ( 17.658 :!: 7.017 vs 11.172 ± 5.019 ova/kg) although the diameter of the ova is larger in the latter species. Spawning activities reach a peak during the spates (August-September) but start on the average one month earlier in C. auratus. These results clearly evidence that the two species have different life history strategies in the waters of Southern Benin and that the degree of iteroparity is higher in C. nigrodigiratus (K-strategy) than in C. aurarus (r-strategy). These demographic traits also suggest that the populations of C. nigrodigirarus would be more affected by the considerable increase of fishing exploitation and intensity attended nowadays in Southern Benin (100-130,000 fishermen in 1987 vs 30,000 in 1982). This hypothesis is supported by the catch statistics that reveal that most (86 % ) C. nigrodigirarus caught in Southern Benin are immature Ph.L. acknowledges an AGCD grant. J.C.P. is Chercheur qualifié FNRS.
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