Reproductive strategy of the annual fish Leptopanchax opalescens (Rivulidae) and trade-off between egg size and maximum body length in temporary wetlands

Abstract

Leptopanchax opalescens is a critically endangered small annual fish. Reproductive traits of this species were studied to improve our understanding of the strategies that facilitate the occupation of temporary wetlands. We compiled egg diameter and maximum total length (TLmax) data from 132 neotropical freshwater fish (83 genera, 43 families) to establish comparisons with this species. We used the egg diameter / TLmax ratio to test the hypothesis that annual fish in temporary wetlands have relatively larger eggs than non-annual species from perennial habitats (lakes, rivers). Fish were collected from Guandu River drainages (Brazil). DNA barcoding was employed to confirm the species identity. The phases of gonadal development and spawn type were described using histological techniques. Egg size and fecundity were determined with microscopic analysis. Females with batch spawning and males with continuous spawning were detected. The bath fecundity ranged from 22–32 vitellogenic oocytes (mean 27 ± 7 SD). Annual species presented greater relative egg size than perennial species (p < 0.001), which is an indication of greater reproductive investment at the expense of somatic growth in temporary wetlands. Larger eggs are advantageous for annual fish as their lifespan is limited, and they can allocate a greater amount of yolk reserves for long periods buried in the substrate under embryonic diapause. Large relative oocytes, spawning in batches, synchronous modal development of oocytes, continued production of sperm in males, and a complex process of embryonic diapause are reproductive traits that favor resilience of L. opalescens and other annual fish in temporary wetlands.