Analysis of the reproductive strategy of Jenynsia multidentata (Cyprinodontiformes, Anablepidae) with focus on sexual differences in growth, size, and abundance

Abstract

Jenynsia multidentata is one of the most abundant freshwater fishes in the subtropical region of South America and when abundant it appears to have a major impact on lake ecosystems function. We studied the life-history traits and population structure of J. multidentata in a shallow lake in Uruguay, and collected literature data along a subtropical to tropical freshwater gradient in South America. Our general focus was on reproductive strategy, particularly on sexual differences in growth, size and abundance. In Lake Blanca, we found strong reverse size dimorphism (RSD) and a feminized sex ratio. Both are attributed to sexual differences in growth patterns and longevity. RSD and a feminized sex ratio seem to characterise J. multidentata regardless of latitude, and together with other life traits such as small size, rapid growth, low age of maturity, the capacity of the females to keep sperm alive to fertilize several successive litters, high natural mortality and fertility, resistance to extreme environmental conditions and omnivory, they are indicative of high productivity to biomass ratio. The very high population growth rate helps to explain why fish removal, aiming to promote an increase in the zooplankton grazing pressure on phytoplankton, may not be a useful tool in eutrophic-turbid subtropical South American lakes. We also found that the duration of the breeding season deviated markedly with latitude, increasing towards the tropics, which may have major consequences for population growth rates and differential impact of this species on lake ecosystems in the different climate zones.