Cannibalism is considered one of the causes of intra-cohort size divergence in fish and is usually believed to result in increased fitness in terms of survival and reproduction, but direct evidence of this is lacking. Population demographics of the clearhead icefish (Protosalanx chinensis) from Lake Xingkai (Khanka) were investigated for one year. Size-frequencies exhibited a bimodal distribution from July through January, where the population diverged into an upper and a lower modal group based on size. Stomach content analysis confirmed the occurrence of cannibalism, where fish belonging to the larger, upper modal group preyed upon those of the smaller, lower modal group. We found P. chinensis does not spawn until all of the oocytes have reached maturity and then a single spawning event occurs although the oocytes may develope asynchronously in the ovary. Upper modal group females matured slightly earlier than those of the lower modal group, and reproductive investment was considerably greater in the upper modal group than the lower modal group. The lower modal males made up the majority of the population after the spawning period, which meant they may have few opportunities to participate in reproduction. Therefore, piscivory and cannibalism of P. chinensis appears to have increased fitness of the fish belonging to the upper modal group and greatly reduced the fitness of those belonging to the lower modal group.

中文翻译：

---

清头冰鱼（Protosalanx chinensis）的生活史特征和群内差异，表明同类相食增加了健康

同类相食被认为是鱼类群内大小差异的原因之一，通常认为会导致生存和繁殖方面的适应性增加，但缺乏直接证据。对来自兴凯湖 (Khanka) 的清头冰鱼 (Protosalanx chinensis) 的种群统计进行了一年的调查。从 7 月到 1 月，大小频率表现出双峰分布，其中人口根据大小分为高低模态组。胃内容分析证实了自相残杀的发生，其中属于较大的较高模态组的鱼捕食较小的较低模态组的鱼。我们找到了 P。chinensis 直到所有卵母细胞都成熟后才会产卵，然后发生单个产卵事件，尽管卵母细胞可能在卵巢中不同步发育。上模态组女性的成熟略早于下模态组，上模态组的生殖投资明显大于下模态组。产卵期后，低阶雄性占人口的大多数，这意味着它们可能很少有机会参与繁殖。因此，P. chinensis 的食鱼和同类相食似乎增加了属于上模态组的鱼的适应度，而大大降低了属于下模态组的鱼的适应度。高模态组的生殖投资明显高于低模态组。产卵期后，低阶雄性占人口的大多数，这意味着它们可能很少有机会参与繁殖。因此，P. chinensis 的食鱼和同类相食似乎增加了属于上模态组的鱼的适应度，而大大降低了属于下模态组的鱼的适应度。高模态组的生殖投资明显高于低模态组。产卵期后，低阶雄性占种群的大多数，这意味着它们可能很少有机会参与繁殖。因此，P. chinensis 的食鱼和同类相食似乎增加了属于上模态组的鱼的适应度，而大大降低了属于下模态组的鱼的适应度。