The recapture of Leptopanchax opalescens (Aplocheiloidei: Rivulidae), a critically endangered seasonal killifish: habitat and aspects of population structure

ABSTRACT Leptopanchax opalescens (Myers, 1942) is a small seasonal killifish endemic to coastal drainages in the state of Rio de Janeiro, Brazil. Leptopanchax opalescens was recaptured in temporary open vegetation pools (22°42.35’S, 43°41.59’W) in the hydrographic basin of the Guandu River, state of Rio de Janeiro, Brazil, after eight years without records. Information on habitat and population parameters (Capture per unit area (CPUA), size, sex ratio and length-weight relationship (LWR)) are given to provide subsidies for the conservation of this species. Specimens were captured during the rainy season (January-April 2020) in shallow pools (mean depth = 21 ± 12 s.d. cm), with relatively acidic pH (5.2 ± 0.8) and low concentrations of dissolved oxygen (3.5 ± 1 mg/L). The estimated CPUA of the population was 0.89 fish/m2. The total length (TL) of males ranged from 21.1 to 28.8 cm, and females ranged from 17.0 to 31.2 mm. Males were significantly larger (t-test = 2.04, p < 0.05) than females, which were in greater proportion (2.83Female: 1Male, p < 0.001). A positive allometric coefficient (b = 3.19) was found through length-weight relationship curve, indicating that individuals of the species gain proportionally more increment in weight than in length. Leptopanchax opalescens is a critically endangered species, and the results of this study contribute to the knowledge of the distribution, population structure and conservation of the species and its natural habitats.

摘要 辉光薄脂鳉（Leptopanchax opalescens）（Myers，1942）是巴西里约热内卢州沿海流域特有的小型季节性鳉鱼。该物种在时隔8年无相关记录后，于巴西里约热内卢州瓜杜河（Guandu River）流域的临时开放式植被池（22°42.35’S，43°41.59’W）中被重新捕获。本研究提供了该物种的栖息地信息与种群参数（单位面积捕获量（Capture per unit area，CPUA）、体型、性比及体长-体重关系（Length-weight relationship，LWR）），旨在为其物种保护提供支撑依据。
研究样本于2020年雨季（1月至4月）采集自浅水池沼，平均水深为21±12标准差（s.d.）厘米，水体呈弱酸性（pH=5.2±0.8），溶解氧浓度较低（3.5±1 mg/L）。该种群的单位面积捕获量估算值为0.89尾/平方米。雄性个体的总长度（TL）范围为21.1~28.8厘米，雌性个体的总长度范围为17.0~31.2毫米。雄性个体体型显著大于雌性（t检验值=2.04，p<0.05）；雌性个体占比更高，雌雄性比为2.83:1（p<0.001）。通过体长-体重关系曲线分析，研究发现该物种的异速生长系数（b=3.19）为正值，表明该物种个体的体重增长幅度相对体长增长幅度更高。
辉光薄脂鳉为极危物种，本研究结果有助于深化对该物种分布、种群结构及其自然栖息地保护的认知。