Cycle annuel de l'indice gonado-somatique et de la condition chez ieux espèces de Chrysichthys (Siluriformes, Bagridae) au lac Nokoué et à la lagune de Porto-Novo au Bénin

The annual cycle of the gonads and the condition have been studied in n=1826 Chrysichthys nigrodigitatus and n=689 C. auratus caught in 1990-1991 by artisanal fishing in Nokoue lake and Porto-Novo lagoon in Benin. The condition factor increases progressively from September to February (maximum in February 1.15 in C. nigrodigitatus and in November 1,1 in C. auratus) then decreases from March to August (absolute minimum in August 0,95 in C. nigrodigitatus and in April 0,88 in C. auratus). C. nigrodigitatus grows faster than C. auratus. Gonads increase slowly in C. nigrodigitatus from February (male I.G.S. = 0,20 %; female I.G.S. = 0,13 %) to April (male I.G.S. = 0,22 %; female I.G.S. = 0,31 %), then rapidly in July (male I.G.S. = 0,46 ; female I.G.S. = 2,8 %). In C. auratus, the I.G.S. cycle is similar with the difference that in August the gonad weight remains high (male IG.S. =3,22 %; female I.G.S. = 3,97 %) and the drop in gonad weight noted in September (male I.G.S. = 0,41 %; female I.G.S. =0,87 %).