Environmental influence on the reproductive strategy of Helogenes marmoratus (Siluriformes: Cetopsidae) in the Amazonian streams

Abstract

The reproductive strategy of a species must be adjusted to variations in environmental conditions to guarantee population balance. Hydrological fluctuations in Amazonian streams of terra firme (non-flooded) are controlled primarily by local rainfall. Fish assemblages are composed predominantly of species of small size. We investigated the reproductive strategy of the cryptic catfish Helogenes marmoratus and assessed the influence of environmental variables (e.g., rainfall, conductivity, habitat descriptors) on its reproductive activity in a catchment of the Guamá River in the eastern Brazilian Amazon. Through monthly collections between March 2019 and March 2020, we identified an extended reproductive period between July 2019 and March 2020. Males mature at smaller sizes than females (♂ = 27.41 mm; ♀ = 31.36 mm). We confirmed batch spawning, low fecundity (59.55 ± 22.76 stage IV oocytes), and large oocytes (1.24 ± 0.15 mm). Our results indicated that H. marmoratus strategy occupies an intermediate place between opportunistic and equilibrium gradient. Multiple regressions showed that thalweg depth, electrical conductivity, leaf litter, and rainfall are important drivers of reproductive activity of females of H. marmoratus, explaining 32% of the variation of the GSI. Our study provides evidence of differentiated reproductive response between the sexes to environmental variables.

Year-round spawning of three tropical Cypriniformes fishes in Southeast Asia

“…Similar year-round presence of reproductively active male fishes has been reported in other freshwater fishes such as in live-bearing poecilid fishes in Costa Rica 54 . This reproductive strategy is thought to be facilitated by the reduced energetic cost of producing spermatozoa compared to oocytes in females 14 .…”

“…In the warm and wet tropics, freshwater fishes commonly exhibit continuous reproduction or reduced seasonality 2 , 8 , 9 . Protracted spawning in tropical species often coincides with the wet season 10 – 14 .…”