Growth and reproduction in captivity unveils remarkable life-history plasticity in the smallnose fanskate, Sympterygia bonapartii (Chondrichthyes: Rajiformes)

ABSTRACT We analyzed growth and reproduction of captive-born smallnose fanskates Sympterygia bonapartii. Egg cases were obtained from oviposition of two females caught in the wild and held at Temaikèn Aquarium. Following hatching, growth was analyzed in 13 females and 21 males until sexual maturity. Pattern of oviposition activity and reproductive performance were evaluated in six of the captive-reared females. Four models were fitted to growth data, among which the logistic function was the one attaining the best fit. The highest growth rate for both sexes was recorded during the first year of life, whereas growth was significantly higher in females than in males during the second year. Size at first oviposition was 61.7 ± 3.5 cm TL, similar to wild specimens. However, captive-reared females reached maturity before two years of age, i.e. much earlier than wild skates, implying a significant phenotypic plasticity in this species. The similarity in size at maturity and the difference in age at maturity between captive and wild specimens indicate that there is a decoupling of both parameters mediated through growth rates. Captive-born skates reproduced successfully and yielded viable offspring, indicating that the environment at Temaikèn Aquarium is suitable for S. bonapartii to attain its full life cycle.

摘要：本研究针对人工繁育的小头犁头鳐（smallnose fanskates，学名Sympterygia bonapartii）的生长与繁殖展开分析。实验所用卵鞘均来自2尾野外捕获、饲养于泰马肯水族馆（Temaikèn Aquarium）的雌性个体的自然产卵。幼体孵化后，研究人员对13尾雌性及21尾雄性个体的生长情况进行跟踪监测直至其达到性成熟。同时选取6尾人工繁育雌性个体，对其产卵行为模式与繁殖性能开展评估。针对生长数据拟合了4种生长模型，其中逻辑斯蒂生长函数（logistic function）拟合效果最优。雌雄个体的最高生长速率均出现在出生后的第一年，而在出生第二年，雌性个体的生长速率显著高于雄性。首次产卵时的全长为61.7 ± 3.5 cm TL（总长度），与野生个体的数值相近。然而人工繁育的雌性个体在2龄前便达到性成熟，远早于野生犁头鳐，这表明该物种具备显著的表型可塑性。人工繁育种群与野生种群在性成熟体长上的相似性，以及性成熟年龄上的差异，证明生长速率介导了体长与年龄两个参数间的解耦效应。人工繁育的小头犁头鳐可成功繁殖并产出可存活子代，表明泰马肯水族馆的饲养环境能够满足该物种完成完整生活史所需的各项条件。