Graduate School of Life Science, Hokkaido University, Kita 10, Nishi 8, Kita-ku, Sapporo, 060-0810, Japan.
Graduate School of Science and Engineering, Ehime University, 2-5 Bunkyocho, Matsuyama, Ehime, 790-8577, Japan.
Sci Rep. 2024 Aug 28;14(1):19300. doi: 10.1038/s41598-024-69755-z.
Cichlid fishes in the African Great Lakes have undergone explosive speciation, acquiring markedly varying ecologies and diets. There are multiple lineages of scale-eating cichlids, and their natural history and evolutionary ecology is only partially understood. We examined the feeding habit of Docimodus evelynae, a known scale eater, in Lake Malawi. The stomach contents of young individuals mainly consisted of unknown 1 mm hard, white warts (> 30%). To clarify the origin of these warts, we conducted an X-ray fluorometer analysis, and found they were rich in sulphur but low in silicon and calcium, suggesting they were epidermal tissues. Histological and morphological analyses revealed they were multicellular and cup-shaped. These characteristics matched only those of the pearl organs of the coexisting cyprinid Labeo cylindricus. DNA was extracted from the warts found in the stomach of five D. evelynae individuals, followed by PCR using primers targeting the partial COI gene of L. cylindricus. The resulting sequences exhibited 98% similarity to those of L. cylindricus. Pearl organs, never reported as a primary food for fish, could offer a substantial nutritional source based on calorific calculations. Understanding how this peculiar diet is foraged is essential for full comprehension of the food-web structure in this lake.
非洲大湖中的慈鲷鱼类经历了爆发性的物种形成，获得了明显不同的生态和饮食。有多条食鳞慈鲷的谱系，它们的自然历史和进化生态学只有部分被了解。我们研究了马拉维湖中已知的食鳞慈鲷 Docimodus evelynae 的摄食习性。幼鱼的胃内容物主要由未知的 1 毫米硬白色疣（>30%）组成。为了阐明这些疣的来源，我们进行了 X 射线荧光计分析，发现它们富含硫，但硅和钙含量低，表明它们是表皮组织。组织学和形态学分析表明它们是多细胞的和杯状的。这些特征仅与共存的鲤科鱼类 Labeo cylindricus 的珍珠器官相匹配。从 5 只 D. evelynae 个体胃中发现的疣中提取 DNA，然后使用针对 L. cylindricus 的部分 COI 基因的引物进行 PCR。得到的序列与 L. cylindricus 的序列相似度为 98%。珍珠器官从未被报道为鱼类的主要食物，但根据热量计算，它可能提供大量的营养来源。了解这种特殊的饮食是如何被觅食的，对于充分理解这个湖中食物网的结构至关重要。
