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Ichthyoplankton (from Greek: ἰχθύς, ''ikhthus'', "fish"; and πλαγκτός, ''planktos'', "drifter") are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals.〔(What are Ichthyoplankton? ) Southwest Fisheries Science Center, NOAA. Modified 3 September 2007. Retrieved 22 July 2011.〕〔 Fish can produce high numbers of eggs which are often released into the open water column. Fish eggs typically have a diameter of about . The newly hatched young of oviparous fish are called larvae. They are usually poorly formed, carry a large yolk sac (for nourishment) and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, a process which depends on typically inadequate zooplankton density, starving many larvae. Ichthyoplankton can be a useful indicator of the state and health of an aquatic ecosystem.〔 For instance, most late stage larvae in ichthyoplankton have usually been preyed on, so ichthyoplankton tends to be dominated by eggs and early stage larvae. This means that when fish, such as anchovies and sardines, are spawning, ichthyoplankton samples can reflect their spawning output and provide an index of relative population size for the fish.〔 Increases or decreases in the number of adult fish stocks can be detected more rapidly and sensitively by monitoring the ichthyoplankton associated with them, compared to monitoring the adults themselves. It is also usually easier and more cost effective to sample trends in egg and larva populations than to sample trends in adult fish populations.〔 ==History== Interest in plankton originated in Britain and Germany in the nineteenth century when researchers discovered there were microorganisms in the sea, and that they could trap them with fine-mesh nets. They started describing these microorganisms and testing different net configurations.〔Moser HG and Watson W (2006) ("Ichthyoplankton" ) Pages 269–319. In: Allen LG, Pondella DJ and Horn MH, ''Ecology of marine fishes: California and adjacent waters'' University of California Press. ISBN 978-0-520-24653-9.〕 Ichthyoplankton research started in 1864 when the Norwegian government commissioned the marine biologist G. O. Sars to investigate fisheries around the Norwegian coast. Sars found fish eggs, particularly cod eggs, drifting in the water. This established that fish eggs could be pelagic, living in the open water column like other plankton.〔 ((Google Translate ))〕 Around the beginning of the twentieth century, research interest in ichthyoplankton became more general when it emerged that, if ichthyoplankton was sampled quantitatively, then the samples could indicate the relative size or abundance of spawning fish stocks.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「ichthyoplankton」の詳細全文を読む スポンサード リンク
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