Reproductive biology of six Barbus species indigenous to Sri Lanka

Synopsis Six Barbus species were sampled monthly in two river systems of SW-Sri Lanka, over a 15 month period. Sex ratio, size at maturity, maximum and modal sizes, distribution of egg sizes in mature ovaries and individual fecundities were measured. Seasonal changes in size distributions, sex ratio, frequency of female gonadal stages and the gonado-somatic index (GSI) were analysed on the basis of the monthly samples. Seasonal cycles in reproductive activity were assessed, using mainly the two last-mentioned parameters and the appearance of young in the populations. It was found that three of the species (B. bimaculatus, B. cumingi, B. vittatus) tend to concentrate their reproductive activities in certain months of the year, roughly coinciding with the seasonal peaks of precipitation. The other three (B. nigrofasciatus, B. dorsalis, B. titteya) spread their reproductive efforts more evenly through the year. Sexual dimorphism with females bigger, relatively early maturation of males, high maximum GSI values, a distinct final mode of large mature ova in the egg-diameter distribution, and a comparatively steep increase of fecundity with body weight or gonad weight were found to be more or less consistently associated with seasonal reproduction.