Schalk Christopher M, Montaña Carmen G, Libson Monika E
Rev Biol Trop. 2014 Mar;62(1):109-17. doi: 10.15517/rbt.v62i1.6567.
The dry Chaco, a semiarid thorn forest, is experiencing some of the highest deforestation rates globally, coupled with the fact that small-bodied fish are at the highest risk of extinction, the killifish inhabiting this region may be some of the most threatened taxa. Yet, aspects of ecology and life history for Neotropical killifishes in the Bolivian Gran Chaco region are completely lacking, and basic life-history data is of critical importance for the design and implementation of conservation measures. Collections were conducted during the early (January 2011) and late (March-April 2011) rainy season using an area-based sampler and dip net surveys. Fish standard length and body depth were measured as well as the number of oocytes per size class, mean oocyte diameter per size class, and total fecundity for the females of each species. A total of 490 specimens of rivulids were captured; Austrolebias vandenbergi: 85 females, 105 males and 39 juveniles, and N. ornatipinnis: 62 females, 113 males, 86 juveniles. Sexual size dimorphism, absolute fecundity, oocyte developmental stages, oocyte diameter, and population sex ratios were determined for each species. Both species exhibited sexual size dimorphism. Male A. vandenbergi exhibited longer standard length (mean +/- SD; males: 27.07 +/- 3.89mm, females: 23.6 +/- 2.02mm) and body depth (males: 8.9 +/- 1.7mm, females: 7.2 +/- 1.1 mm) as compared to females. Male N. ornatipinnis had a similar pattern for both standard length (males: 26.0 +/- 7.1mm, females: 19.1 +/- 5.83mm) and body depth (males: 5.6 +/- 1.9mm, females: 4.7 +/- 1.0mm). Austrolebias vandenbergi had fewer and smaller oocytes per female (47 +/- 31.6) than N. ornatipinnis (206 +/- 131.2). There was a positive relationship between fecundity and female body size in both species. The presence of multiple developmental stages of oocytes (immature, maturing, and mature) suggest that both species of rivulids exhibit fractional spawning, a reproductive strategy that enhances reproductive success in these extreme habitats. Neofundulus ornatipinnis exhibited a higher mean oocyte diameter for all three developmental stages (immature, maturing, and mature) as compared to A. vandenbergi. Austrolebias vandenbergi exhibited an equal adult sex ratio (males:females, 1:1), but there was a slight female biased ratio for N. ornatipinnis (males:females, 1:1.8). These results provide fundamental and valuable information for ensuring rivulid conservation in tropical regions, and also improve the knowledge on the biology and ecology of these poorly known species. To our knowledge, this study represents the first contribution on the reproductive biology of two Neotropical annual rivulid fishes (Austrolebias vandenbergi and Neofundulus ornatipinnis) inhabiting semi-permanent and ephemeral ponds in the Gran Chaco of Southeastern Bolivia.
干燥的查科地区是一片半干旱的荆棘林，正经历着全球最高的森林砍伐率，同时小型鱼类面临着最高的灭绝风险，栖息在该地区的鳉鱼可能是受威胁最严重的一些分类群。然而，玻利维亚大查科地区新热带鳉鱼的生态和生活史方面完全缺乏相关研究，而基本的生活史数据对于保护措施的设计和实施至关重要。在雨季早期（2011年1月）和晚期（2011年3月至4月）进行了采集，使用基于面积的采样器和抄网进行调查。测量了鱼类的标准长度、体深，以及每个大小类别的卵母细胞数量、每个大小类别的平均卵母细胞直径和每个物种雌性的总繁殖力。总共捕获了490个溪鳉科标本；范氏澳鳉：85只雌性、105只雄性和39只幼鱼，以及饰鳍新底鳉：62只雌性、113只雄性、86只幼鱼。确定了每个物种的两性异形、绝对繁殖力、卵母细胞发育阶段、卵母细胞直径和种群性别比。两个物种都表现出两性异形。与雌性相比，雄性范氏澳鳉的标准长度（平均值±标准差；雄性：27.07±3.89毫米，雌性：23.6±2.02毫米）和体深（雄性：8.9±1.7毫米，雌性：7.2±1.1毫米）更长。雄性饰鳍新底鳉在标准长度（雄性：26.0±7.1毫米，雌性：19.1±5.83毫米）和体深（雄性：5.6±1.9毫米，雌性：4.7±1.0毫米）方面也有类似模式。范氏澳鳉每个雌性的卵母细胞数量和大小都比饰鳍新底鳉少（47±31.6个）（206±131.2个）。两个物种的繁殖力与雌性体型之间都存在正相关关系。卵母细胞存在多个发育阶段（未成熟、成熟和成熟）表明，这两种溪鳉科物种都表现出分批产卵，这是一种在这些极端栖息地提高繁殖成功率的繁殖策略。与范氏澳鳉相比，饰鳍新底鳉在所有三个发育阶段（未成熟、成熟和成熟）的平均卵母细胞直径都更高。范氏澳鳉的成年性别比相等（雄性：雌性，1:1），但饰鳍新底鳉的性别比略有偏向雌性（雄性：雌性，1:1.8）。这些结果为确保热带地区溪鳉科鱼类的保护提供了基础且有价值的信息，也增进了对这些鲜为人知物种的生物学和生态学的了解。据我们所知，这项研究是关于栖息在玻利维亚东南部大查科地区半永久性和临时性池塘中的两种新热带一年生溪鳉科鱼类（范氏澳鳉和饰鳍新底鳉）繁殖生物学的首次贡献。
