Reproductive plasticity of Hypostomus affinis (Siluriformes: Loricariidae) as a mechanism to adapt to a reservoir with poor habitat complexity

Silvana Duarte,Nilo Bazzoli,Francisco Gerson Araújo

doi:10.1590/s1984-46702011000500005

Abstract

In this work we describe the gonad morphology and spawning season of Hypostomus affinis (Steindachner, 1877) in a tropical reservoir based on 55 males and 125 females. Our aim was to assess eventual adaptations in reproductive tactics developed by this riverine species inhabiting an oligotrophic reservoir with low habitat complexity, few rocks and few other preferred consolidated substrata. We described the stages of cells of reproductive lineage, gonadal development and some reproductive traits which were compared with information in the available literature. Cells from the spermatogenic lineage were spermatogonia, spermatocytes, spermatids and spermatozoa, and cells from the oocytarian lineage were primary oocytes, previtelogenic oocytes, cortical vesicle oocytes and yolk globules or vitellogenic. Five stages were described for the males/females according to the distribution of oocytes and spermatogenic lineage cells: resting; initial maturation; advanced maturation; partially spent/spawned; totally spent/spawn. Females outnumbered males and reached larger size. Synchronic ovary development in two groups was found with diameter of mature oocytes ranging from 2 to 3.35 mm. Indication of early maturation, a longer reproductive period and the production of smaller eggs in small clutches seems to be features of the reservoir population not found in riverine systems. Such changes in tactics may indicate a shift to an opportunistic strategy, helping the population to withstand environmental constraints and to succeed in this oligotrophic and poorly structured reservoir.

Highlights

Knowledge on the reproductive strategy and tactics such as sex ratio, gonadal development and breeding season are essential in order to obtain a comprehensive understanding of the population dynamics of any fish species (WINEMILLER 1989, WOOTTON 1989, LASSALA & RENESTO 2007, TAMADA 2009)
Hypostomus affinis (Steindachner, 1877) is a detritivorous species from the Paraiba do Sul River basin that has successfully adapted to the Lajes Reservoir (DUARTE & ARAÚJO 2000), an oligotrophic environment constructed between 1905 and 1908, surrounded by well-preserved stretches of Atlantic rainforest (SANTOS et al 2004)
In this study we describe features of the reproductive biology of H. affinis and assess the tactics that this species uses to succeed in the Lajes Reservoir, a lentic, low structured impoundment where the preferred habitat of the species are scarce

Summary

Introduction

Knowledge on the reproductive strategy and tactics such as sex ratio, gonadal development and breeding season are essential in order to obtain a comprehensive understanding of the population dynamics of any fish species (WINEMILLER 1989, WOOTTON 1989, LASSALA & RENESTO 2007, TAMADA 2009). Studies on the reproductive biology of H. affinis in in the Paraíba do Sul River encompass sex ratio (MAZZONI & CARAMASCHI 1995), ovarian de development, fecundity and spawning season (MAZZONI & CARAMASCHi 1997). They concluded that this species adopts an equilibrium (sensu WINEMILLER) reproductive strategy characterized by a suite of attributes associated with parental care, maturation, large eggs and seasonal reproduction. In this study we describe features of the reproductive biology of H. affinis and assess the tactics that this species uses to succeed in the Lajes Reservoir, a lentic, low structured impoundment where the preferred habitat of the species (rocks, stones and gravel) are scarce. We hypothesized that some of the reproductive tactics (e.g., sex ratio, size of oocytes, oocytes development) of our population differ from the equilibrium strategies, reported for most loricariid Siluriformes

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