A Diet of Snow: Energetics and Nutrition of Leptocephalus Larvae

细头鱼是五目硬骨鱼的巨大透明的幼虫。它们分布在世界海洋的暖温带和热带纬度地区，在繁殖高峰期是蓝水微浮游动物/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。从他们的发现到1993年的230年间，从未观察到I期钩头龙的肠道内有食物。然而，最近的组织学证据表明，I期头鲸可能会吞食幼虫和浮游动物的粪便颗粒。进一步的证据表明，颗粒物有机物质（POM）和溶解性有机物质（DOM）是重要的营养来源。微粒和溶解的有机物质构成了世界海洋中主要的碳库，但它们对远洋后生动物的意义仍然是一个谜。为了描述钩头鱼的营养生态位，将对幼虫窝和幼虫进行检查，并确定两者的蛋白聚糖结构；将检查四种不同物种的肠道形态（包括肠道内容物，如果存在的话）。营养摄取的位置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确定单个幼虫的饮食消耗率来量化。幼虫的生长将通过耳石的微增量分析来确定，并与RNA DNA分析确定的生长指标进行比较。近似组成和元素组成将为生物种群及其日常生产中储存的卡路里和碳提供价值。钩头虫幼虫可能是脊椎动物中唯一从DOM和POM中获取营养的例子。如果是这样的话，钩头鲸将在远洋食物网中构成一个独特的营养环节。我们的研究将解答头端鱼如何获取和利用能量的谜题，并描述头端鱼幼虫在上层营养等级中的地位。

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.