Reproductive and morphological analysis of the trairão Hoplias intermedius in the São Francisco River, downstream from a large reservoir

Abstract

AbstractHoplias intermedius, of the Characiformes order and Erytrinidae family, is widely distributed across South America. This commercially interesting species can reach a length of 100 cm and a weight of 15–20 kg. To evaluate the reproductive biology of H. intermedius in the São Francisco River, Brazil, 154 males and 190 females were captured bi‐monthly between September 2018 and August 2019 from the downstream regions of the Três Marias dam. Gillnets with differently sized meshes were deployed at distances of 34–54 km after the confluence with the Abaeté River (18°00′49″ S, 45°10′51″ W). Biometric data, gonadosomatic index (GSI), Fulton condition factor (K) and absolute fecundity (AF) were determined for each specimen. Gonad maturation stages and the spawning season were also established. The biometric data, GSI and K average values were relatively higher in females than in males. The reproductive peak for both sexes was reached around January/February. The mean AF was 4300.5 ± 1451.2 follicles per female. Fully developed vitellogenic follicles had a mean diameter of 1014.8 ± 250.7 μm, which is characteristic of fish with moderate fecundity. Fish of all maturation stages, from mature, spawned and spermed, occurred in all bimesters, indicating that this species reproduced throughout the year. The high frequency of spawning females throughout the year and the histological characteristics of spawned ovaries indicated that trairão H. intermedius' spawning type is partial.