Abstract Sagittal otolith pairs were extracted from two-hundred-and-twenty-six giant African threadfin Polydactylus quadrifilis collected from the Kwanza Estuary in Angola between 2016 and 2018 ranging in size from 160 to 1360 mm fork-length (FL) and from one to 23 years of age (26 juvenile, 170 male, nine intersex and 27 female). An additional 85 otolith pairs (24 male, six female and 55 unsexed) were extracted in the same region between 2007 and 2014 (475−1525 mm FL, 2–23 years) and were utilised solely for modelling growth. Otolith aging revealed rapid growth and early maturation (L50 = 399.2 mm FL, A50 = 1.50 years). Sex change occurred over a wide size (790−1125 mm FL) and age (3–8 years) range and was initiated at 1082.3 mm FL and 6.2 years and completed at 1127.4 mm FL and 7.06 years. Strong evidence was provided for partial protandry in P. quadrifilis via the presence of several extremely old male fish, including one individual of 22 years and noticeable differences in length-at-age were observed between older male and female fish. To investigate potential life-history variability, three approaches were taken to group individuals and assess for improvements in model fit using the von Bertalanffy Growth Function (VBGF). Subgroups were determined by sex in Approach 1 and by predicted life-history pathway (‘changers’ & ‘non-changers’) in Approaches 2 (individuals on sex change pathways have increased growth following sex change) & 3 (individuals on sex change pathways have increased growth throughout ontogeny). In all approaches, differences were observed in the L∞ and k values between fish presumed to change sex and those presumed not to change sex. When compared to the conventional model produced for the entire population, all approaches produced considerably better model fit (Approach 1 = ΔAkaike Information Criterion (ΔAIC) = 64.7, Approach 2 – ΔAIC = 56.1 and Approach 3 – ΔAIC = 136.3) and Approach 3 produced better fit than Approach 1. This suggests that utilising conventional modelling techniques may be inappropriate for the stock assessment and management of sequential hermaphrodites and indicates that a revision of age-growth modelling techniques is required for species with multiple developmental pathways in order to maintain intrapopulation diversity and preserve resilience.

中文翻译：

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当代年龄增长模型是否忽略了突出鱼类的生活史复杂性？大型突出多线虫，巨型非洲线鳍 Polydactylus quadrifilis 的案例研究

摘要 矢状耳石对是从 2016 年至 2018 年间从安哥拉宽扎河口采集的 226 对巨型非洲线鳍 Polydactylus quadrifilis 中提取的，其大小从 160 到 1360 毫米叉长（FL）和从 1 到23 岁（26 名少年，170 名男性，9 名双性人和 27 名女性）。2007 年至 2014 年期间（475-1525 毫米 FL，2-23 岁）在同一地区提取了另外 85 对耳石（24 对男性，6 对女性和 55 对无性别），仅用于模拟生长。耳石老化显示出快速生长和早熟（L50 = 399.2 mm FL，A50 = 1.50 年）。性别变化发生在很宽的体型（790-1125 mm FL）和年龄（3-8 岁）范围内，从 1082.3 mm FL 和 6.2 岁开始，在 1127.4 mm FL 和 7.06 岁完成。为 P 的部分前突提供了强有力的证据。quadrifilis 通过存在几条非常老的雄性鱼，包括一条 22 岁的个体，并且在年龄较大的雄性和雌性鱼之间观察到显着的年龄差异。为了研究潜在的生活史变异性，采用三种方法对个体进行分组，并使用 von Bertalanffy 生长函数 (VBGF) 评估模型拟合的改进。亚组由方法 1 中的性别和方法 2（性变化路径上的个体在性变化后生长增加）和 3（性变化路径上的个体）中预测的生活史途径（“改变者”和“非改变者”）决定在整个个体发育过程中增加了生长）。在所有方法中，在假定改变性别的鱼和假定不改变性别的鱼之间观察到 L∞ 和 k 值的差异。