A secret snack: the diet of two key mesopelagic Antarctic fish species (Myctophidae: Electrona) is dominated by Arthropods and so far, overlooked gelatinous prey.

In the Southern Ocean, myctophids are the most successful pelagic fish group in terms of diversity, biomass, and abundance. They represent a major trophic link between primary consumers and megafauna, couple the surface and mesopelagic depths, and also represent an alternative trophic pathway in years where krill is scarce. Traditional stomach content analyses have often indicated that myctophids are major krill and copepods consumers, but have shown a bias towards soft-bodied organisms such as gelatinous zooplankton (GZP) and pteropods. In this study, we present a multimarker (COI and 18S) DNA metabarcoding analysis of the diets of two abundant myctophids in the Scotia Sea: Electrona antarctica and Electrona carlsbergi, with a particular focus on easily digestible taxa. Our findings reveal a diverse array of taxa in the diets of these species, primarily copepods and euphausiids, followed by pteropods and GZP. This comprehensive approach allowed us to test and confirm our hypothesis that GZP are common in the diets of both species. Specifically, salps and appendicularians are crucial components of the diet for E. carlsbergi, while hydrozoans play a secondary role in the diet of E. antarctica. Notably, E. carlsbergi consumed more appendicularians, chaetognaths, and hydrozoans during spring in the northern region of the Scotia Sea, while in autumn in the southern region, they prayed more on salps (predominantly Ilhea racovitzai) and other cnidarians. Our study contributes to a more nuanced understanding of the dietary habits of these pelagic fish species and the ecological dynamics of the Scotia Sea.

在南大洋中，灯笼鱼类（myctophids）是在物种多样性、生物量及丰度方面均为最具优势的浮游鱼类类群。它们是初级消费者与巨型动物之间的关键营养级纽带，连接了表层大洋与中层深海生境，同时在磷虾资源匮乏的年份，亦可作为一条替代性的营养通路。传统胃含物分析通常表明，灯笼鱼类主要以磷虾和桡足类为食，但这类分析存在对软体生物的偏好偏差，例如凝胶状浮游动物（GZP）与翼足类。
本研究针对斯科舍海（Scotia Sea）两种优势灯笼鱼类——南极灯笼鱼（Electrona antarctica）和卡氏灯笼鱼（Electrona carlsbergi）的食性，开展了基于COI与18S的多标记物DNA元条形码分析，并重点关注易消化的类群。研究结果显示，这两种鱼类的食谱涵盖丰富类群，主要为桡足类与磷虾类，其次为翼足类和凝胶状浮游动物（GZP）。该综合性分析方法使我们得以验证并确认“凝胶状浮游动物在两种灯笼鱼的食谱中均较为常见”这一假说。
具体而言，海樽与尾海鞘类是卡氏灯笼鱼食谱中的关键组成部分，而水螅虫类则在南极灯笼鱼的食性中扮演次要角色。值得注意的是，在斯科舍海北部海域的春季，卡氏灯笼鱼会更多捕食尾海鞘类、毛颚类与水螅虫类；而在南部海域的秋季，它们则更多捕食海樽（主要为*Ilhea racovitzai*）及其他刺胞动物。本研究有助于更细致入微地阐明这类浮游鱼类的食性习惯与斯科舍海的生态动态。