Reproductive biology of Hyphessobrycon eques (Characiformes: Characidae) in Southern Pantanal, Brazil

Abstract Population and reproductive aspects allow the knowledge and understanding of population dynamics and the influence of environmental factors, in addition to ensure the success of a species continuity. Thus, the aim of this study was to analyze population and reproductive traits of the species Hyphessobrycon eques in southern Pantanal, Brazil. Monthly samplings were conducted from February/2009 to January/2011, with 617 individuals analyzed, being 365 females and 262 males. A similar form of distribution in length and weight between the sexes was observed. There was no significant variation in sex ratio over time, with higher proportion of females during the entire sampled period. Both sexes presented a angular coefficient of Weight/Length (b) relationship greater than 3, with speed of increase in weight greater than in length. For females, a long reproductive period was observed, with greater reproductive intensity from January through June. No significant correlation was observed between the Gonadosomatic Index (GSI) and the average temperature, rainfall and river level, despite the fact that reproductive activity occurs in autumn/winter, when there are favorable conditions due to flooding. The size at first maturation (L50) was 20.2 mm, with confidence interval varying from 19.7 through 20.7 mm. The average fecundity was 191.9 oocytes/females and was significantly related to the standard length and total weight (g), demonstrating a relation with energy accumulation to invest in reproduction. The long reproductive period, intensified by partial spawning, higher proportion of females and low L50, show that the species has strategies necessary for survival and rapid population growth, common in small species characterized as r-strategists.

种群与繁殖特征是认知种群动态、解析环境因子影响的核心内容，同时也是保障物种延续成功的关键基础。为此，本研究针对巴西潘塔纳尔南部地区的Hyphessobrycon eques物种，开展其种群与繁殖特征的分析。研究于2009年2月至2011年1月期间进行月度采样，共分析617尾个体，其中雌性365尾、雄性262尾。
两性在体长与体重的分布上呈现相似特征。种群性比随时间无显著变化，整个采样周期内雌性占比均高于雄性。两性的体重-体长异速生长系数（b）均大于3，表明体重的增长速率高于体长。
雌性个体具有较长的繁殖周期，繁殖强度在1月至6月期间达到峰值。尽管繁殖活动发生在秋季/冬季，此时洪水带来了适宜的生存条件，但研究未发现性腺体指数（Gonadosomatic Index, GSI）与平均气温、降雨量及河流水位之间存在显著相关性。
该物种的初次性成熟体长（L50）为20.2 mm，置信区间为19.7 mm至20.7 mm。平均繁殖力为191.9枚卵/雌性个体，且繁殖力与标准体长和总体重（g）呈显著正相关，表明其繁殖投入与体内能量积累密切相关。
较长的繁殖周期、分批产卵的繁殖方式、较高的雌性占比以及较低的初次性成熟体长，均表明该物种具备生存与种群快速增长所需的适应性策略，这是被归类为r-对策者的小型鱼类的典型特征。