A Diet of Snow: Energetics and Nutrition of Leptocephalus Larvae

细头鱼是五目硬骨鱼中异常巨大、透明的幼虫。它们分布在世界各地的暖温带和热带地区，在繁殖高峰期，它们是蓝水微型浮游动物/大型浮游动物群落的重要组成部分。然而，它们的重要性不在于数量和生物量，而在于它们(极地海洋除外)是全球分布的独特营养专家群体。从它们的发现到1993年，在230年的时间里，从未观察到肠道中有食物的I期小头盖骨。然而，最近的组织学证据表明，I期细头鱼可能会摄取幼虫的房屋和浮游动物的粪便颗粒。进一步的证据表明，颗粒有机物(POM)和溶解有机物(DOM)提供了重要的营养来源。颗粒和溶解的有机物质都构成了世界海洋中的主要碳库，但它们对远洋后生生物的意义仍然是个谜。为了描述细头鱼的营养生态位，将检查幼虫的房屋和幼虫，并确定两者的蛋白多糖结构；将检查四个不同物种的肠道形态(包括肠道内容物，如果存在)。营养吸收的部位将通过放射性标记氨基酸和放射自显影来确定。每日代谢需求将通过测定个体幼虫的饲料消耗率来量化。幼虫的生长将通过耳石的微增量分析来确定，并与由RNA DNA分析确定的生长指数进行比较。近似和元素组成将提供储存在生活人口及其日常生产中的卡路里和碳的价值。细头鱼幼体可能是唯一一种从DOM和POM中获取营养的脊椎动物。如果是这样的话，细头鱼将构成远洋食物网中一条独特的营养链条。我们的研究将解开小头鱼如何获取和利用能量的谜团，并描述小头鱼幼虫在中上层营养等级中的位置。

Leptocephali are the unusually large, transparent larvae of five orders of bony fishes. They are found at warm temperate and tropical latitudes throughout the world ocean and during peak periods of reproduction form an important component of the blue water micronekton/macrozooplankton community. However, their importance is not one of numbers and biomass, it is in the fact that they are (polar oceans excepted) a globally distributed group of unique trophic specialists. For the 230 years between their discovery and 1993, a phase I leptocephalus was never observed with food in its gut. However, recent histological evidence suggests that phase I leptocephali may ingest larvacean houses and zooplankton fecal pellets. Further evidence suggests that particulate organic material (POM) and dissolved organic matter (DOM) provide an important source of nutrition. Both particulate and dissolved organic material comprise the major carbon reservoir in the world ocean, yet their significance to pelagic metazoan life remains a cipher. To describe the leptocephalus trophic niche, larvacean houses and the larvae will be examined and the proteoglycan structure of both will be determined; gut morphology will be examined (including gut contents, if present) in four different species. Sites of nutrient uptake will be determined via radiolabelled amino acids and autoradiography. Daily metabolic demands will be quantified by determining diel consumption rates of individual larvae. Growth of the larvae will be determined by microincremental analysis of otoliths and compared to growth indices determined by RNA DNA analysis. Proximate and elemental composition will provide values for the calories and carbon stored in the living populations and their daily production. The leptocephalus larval form may be the only example of a vertebrate that obtains its nutrition from DOM and POM. If this is the case, leptocephali would comprise a unique trophic link in the pelagic food web. Our research will answer the riddle of how leptocephali acquire and utilize energy and describe the leptocephalus larva's position in the trophic hierarchy of the pelagial.