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Whether fish sleep is an intriguing question, to the point of having inspired the title of several popular science books.〔Feldman, D. (1989) When do fish sleep? And other imponderables of everyday life. Harper and Row, New York.〕〔Weis, J.S. (2011) Do fish sleep? Fascinating answers to questions about fishes. Rutgers University Press, New Brunswick.〕 In birds and mammals, sleep is defined by eye closure and the presence of typical patterns of electrical activity in the brain, including the neocortex, but fish lack eyelids and a neocortex. Some species that always live in shoals or that swim continuously (because of a need for ram ventilation of the gills, for example) are suspected never to sleep. There is also doubt about certain blind species that live in caves.〔Parzefall, J. (1993): Behavioural ecology of cave-dwelling fish; pp. 573–606 ''in'': Pitcher, T.J.(ed.), The Behaviour of Teleost Fish; London: Chapman&Hall.〕 Other fish seem to sleep, however, especially when purely behavioral criteria are used to define sleep. For example, zebrafish,〔Zhdanova, I.V., Wang, S.Y., Leclair, O.U., and Danilova, N.P. (2001) Melatonin promotes sleep-like state in zebrafish, Brain Research 903: 263–268. Yokogawa T, Marin W, Faraco J, Pézeron G, Appelbaum L, et al. (2007) Characterization of Sleep in Zebrafish and Insomnia in Hypocretin Receptor Mutants, PLoS Biology Vol. 5, No. 10, e277 (and criticism and rebuttal, at PLoS Biology )〕 tilapia,〔Shapiro, C.M., and Hepburn, H.R. (1976) Sleep in a schooling fish, ''Tilapia mossambica'', Physiology and Behavior 16:613–615〕 tench,〔Peyrethon, J., and Dusan-Peyrethon, D. (1967) Étude polygraphique du cycle veille-sommeil d'un téléostéen (''Tinca tinca''), Compte-Rendus de la Société de Biologie 161: 2533-2537〕 brown bullhead,〔Titkov, E.S. (1976) Characteristics of the daily periodicity of wakefulness and rest in the brown bullhead (''Ictalurus nebulosus''), Journal of Evolutionary Biochemistry and Physiology 12:305–309.〕 and swell shark〔Nelson, D.R.,and Johnson, R.H. (1970) Diel activity rhythms in the nocturnal, bottom-dwelling sharks ''Heterodontus francisci'' and ''Cephaloscyllium ventriosum'', Copeia 1970: 732–739.〕 become motionless and unresponsive at night (or by day, in the case of the swell shark); Spanish hogfish and blue-headed wrasse can even be lifted by hand all the way to the surface without evoking a response. On the other hand, sleep patterns are easily disrupted and may even disappear during periods of migration, spawning, and parental care.〔Reebs, S.G. (2002) Plasticity of diel and circadian activity rhythms in fish, Reviews in Fish Biology and Fisheries 12: 349–371.〕 == Behavioural sleep == Instead of examining brain activity for sleep patterns, an alternate approach is to examine any rest/activity cycles that might indicate "behavioural sleep". The following four behavioural criteria are characteristic of sleep in birds and mammals and could be extended to fishes: (1) prolonged inactivity; (2) typical resting posture, often in a typical shelter; (3) alternation with activity in a 24-h cycle; (4) high arousal thresholds. Based on these criteria, many fish species have been observed sleeping.〔 The typical sleep posture of the brown bullhead is with the fins stretched out, the tail lying flat on the bottom, the body inclined to one side at an angle of 10-30 degrees to the vertical, the cardiac and respiratory frequencies much slower than normal, and much less sensitivity to sound and to being touched.〔Titkov, E.S. (1976) Characteristics of the daily periodicity of wakefulness and rest in the brown bullhead (''Ictalurus nebulosus''), Journal of Evolutionary Biochemistry and Physiology 12: 305-309.〕〔Karmanova, I.G., Belich, A.I., and Lazarev, S.G. (1981) An electrophysiological study of wakefulness and sleeplike states in fish and amphibians, pp. 181-202 ''In'': Brain Mechanisms of Behaviour in Lower Vertebrates (P.R. Laming, ed.). Cambridge University Press, Cambridge.〕 Mozambique tilapia are motionless at the bottom at night, with a lower respiratory rate and no eye movement, and they do not respond as readily as during the day to electrical currents or food delivery.〔Shapiro, C.M., and Hepburn, H.R. (1976) Sleep in a schooling fish, ''Tilapia mossambica''. Physiology and Behavior 16: 613-615.〕 At night, Spanish hogfish, bluehead wrasse, the wrasse ''Halichoeres bivittatus'', the cunner ''Tautogolabrus adspersus'', and even requiem sharks, can be picked up by hand without eliciting a response.〔 Tauber, E.S., Weitzman, E.D., and Korey, S.R. (1969) Eye movements during behavioral inactivity in certain Bermuda reef fish. Communications in Behavioral Biology A 3: 131-135.〕〔Tauber, E.S. (1974) The phylogeny of sleep, pages 133-172 ''In'': Advances in sleep research, vol. 1 (E.D. Weitzman, ed.). Spectrum Publications, New York.〕〔Clark, E. (1973) “Sleeping” sharks in Mexico. Underwater Naturalist 8: 4-7.〕〔Dew, C.B. (1976) A contribution to the life history of the cunner, ''Tautogolabrus adspersus'', in Fishers Island Sound, Connecticut. Chesapeake Science 17: 101-103.〕 A 1961 observational study of approximately 200 species in European public aquaria reported many cases of apparent sleep.〔Weber, E. (1961) Über Ruhelagen von Fischen, Zeitschrift für Tierpsychologie 18: 517–533.〕 Divers can easily see fishes settling down for the night in typical shelters, such as holes and crevices, underneath ledges, amidst vegetation, inside sponges, or buried in sand.〔Reebs, S.G. (1992) Sleep, inactivity, and circadian rhythms in fish. Pp. 127-135 ''In'' Rhythms in Fishes (M.A. Ali, editor). Plenum, New York.〕 Some extra protection can be derived from special secretions, such as the mucous envelope produced by several species of wrasse and parrotfish, either around the fish themselves or at the opening of their shelter. These envelopes screen the sleeping fish from predators〔 Winn, H.E., and Bardach, J.E. (1959) Differential food selection by moray eels and a possible role of the mucous envelope of parrot fishes in reduction of predation. Ecology 40: 296-298.〕 and ectoparasites.〔 Grutter, A.S., Rumney, J.G., Sinclair-Taylor, T., Waldie, P., and Franklin, C.E. (2011) Fish mucous cocoons: the "mosquito nets" of the sea. Biology Letters 7: 292-294.〕 In the laboratory, periods of inactivity often alternate with periods of activity on a 24-h basis, or a near 24-h basis when the lighting conditions are constant. Circadian rhythms of activity have been documented in over 40 different fish species, including hagfish, lamprey, sharks, cyprinids, ictalurids, gymnotids, salmonids, and labrids.〔 Reebs S.G. (2011) Circadian Rhythms in Fish. ''In'': Farrell A.P., (ed.), Encyclopedia of Fish Physiology: From Genome to Environment, volume 1, pp. 736–743. San Diego: Academic Press.〕〔 Zhdanova, I. and S.G. Reebs. (2006) Circadian rhythms in fish. Pp. 197-238 ''In'' Fish Physiology, Vol 24: Behaviour and Physiology of Fishes (K.A. Sloman, R.W. Wilson, and S. Balshine, eds.). Elsevier, New York.〕 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「Sleep in fish」の詳細全文を読む スポンサード リンク
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