Equilibrium reproductive strategy of the armored catfish Hypostomus auroguttatus (Siluriformes, Loricariidae) in a tropical river in Southeastern Brazil

Abstract

We investigated the reproductive strategy developed by the armored catfish Hypostomus auroguttatus Kner 1854 in a tropical river of Southeastern Brazil. A total of 173 females (157–370 mm TL) and 165 males (140–357 mm TL) were analyzed. Sex ratio (1 female: 1.05 male) was well balanced. Six stages of oogenesis and five of spermatogenesis were described. Oocyte development was synchronic in two groups, with oocyte size ranging from pre-spawning (<200 μm) to spawning (600–1,000 μm), followed by a sharp decrease in the postspawning (200–360 μm) phase. Macroscopic oocyte diameter ranged from 0.1 mm to 7.2 mm, with vitellogenic ones ranging from 4.8 to 7.2 mm. Spawning occurred throughout most of the year, peaking in September-October. Mean batch fecundity was 411 oocytes ranging from 163 to 662 vitellogenic oocytes (relative fecundity = 2.26 oocytes g−1). These attributes, associated with parental care and a wide reproductive period, corresponded to an equilibrium strategy that has proved to be effective in this tropical river. The dominance of H. auroguttatus in rivers, compared with the congeneric Hypostomus affinis that dominates in impoundments, could be associated to larger egg size and lower fecundity in H. auroguttatus, an adaption toward equilibrium strategy that seems to be efficient to this species succeed in running waters. The hypothesis that equilibrium reproductive strategy for fish species is favored in more, predictable environments was confirmed.