The morphological and physiological characteristics of the testes and the sperm of the catfish Heterobranchus longifilis (Val.) are presented. The effect of cryopreservation on the fertilizing capacity of the sperm was also evaluated. Testicular structure and spermatogenesis are described using histological techniques. The coexistence in the lobules of spermatozoa and all the spermatogenic stages indicates that this species is able to perform continuous reproduction. No seasonal trend was noticed in the evolution of the gonadosomatic index and in the quantity of the sperm produced over a year’period. However, maximum sperm production was observed in April and September. Different cryopreservation trials were conducted using a cryoprotective solution composed of 5% dimethyl sulphoxide (DMSO), 5% glycerol, 10% hen's eggyolk and 80% Mounib's solution. Fresh and cryopreserved semen gave equivalent hatching rates (81.1%, 83.4% and 78.9% respectively for the fresh, the 1‐hour cryopreserved and the 8‐month cryopreserved sperm). Percentages of normal and deformed larvae were not affected by sperm cryopreservation.