lab7 - CSIRO PUBLISHING Marine Freshwater Research &...

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CSIRO PUBLISHING Volume 50 , 1999 © CSIRO Australia 1999 A journal for the publication of original contributions in physical oceanography , marine chemistry, marine and estuarine biology and limnology www.publish.csiro.au/journals/mfr All enquiries and manuscripts should be directed to Marine and Freshwater Research CSIRO PUBLISHING PO Box 1139 (150 Oxford St) Collingwood Telephone: 61 3 9662 7618 Vic. 3066 Facsimile: 61 3 9662 7611 Australia Email: ann.grant@publish.csiro.au Published by CSIRO PUBLISHING for CSIRO Australia and the Australian Academy of Science & Marine Freshwater Research
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Introduction Freshwater and marine bony fishes are usually stenoha- line (Jobling 1995), whereas euryhaline fishes are able to live in habitats of fluctuating salinities, such as estuaries (Evans 1993; Madsen et al. 1996), or pass through different phases of both marine and freshwater habitats during their life history (Hoar 1988; Boeuf 1993). There are, however, some fishes with euryhaline capabilities that rarely encounter wide salinity fluctuations in their natural habitat; one of these is the freshwater blenny, Salaria fluviatilis (Asso 1801), which inhabits freshwater habitats and is widely distributed through- out the northern and eastern parts of the Mediterranean basin (Steinitz 1954; Kosswig 1967). Although the population in Lake Kinneret (Sea of Galilee, Israel) has not encountered salinity fluctuations since the upper Pliocene, the fish may tolerate exposure to water of salinity up to that of full- strength sea water (Plaut 1998). The marine peacock blenny, Salaria pavo (Risso, 1810), is closely related to S. fluviatilis and inhabits intertidal rocky coasts of the Mediterranean and European Atlantic coasts (Fishelson 1963; Zander 1973). Kosswig (1967) considered S. fluviatilis to be a polytopic derivative of S. pavo , and Zander (1973) postulated a eurythermal and euryhaline common ancestor for both species. As in S. fluviatilis , S. pavo also tolerates exposure to a wide range of salinities from full- strength sea water to fresh water (Plaut 1998). The effect of environmental salinity on the metabolic rates of fishes has been well studied (see review by Kirschner 1993, 1995; Peterson and Meador 1994). However, the phys- iological responses of fish to salinity change may be complex; salinity may affect a number of physiological systems, and salinity rarely changes in isolation from other environmental factors, such as temperature and concentrations of dissolved oxygen and CO 2 (Wheatly 1988). Studies of the effects of salinity on fishes often use oxygen consumption to estimate the metabolic cost of osmoregula- tion; this cost is expected to be lowest for fishes in an iso- osmotic environment, and is expected to increase as salinity increases or decreases and the medium becomes hyper- or hypo-osmotic to the body fluids (Febry and Lutz 1987). This holds if it is assumed that the permeability of gills remains constant (but see Gordon 1963; Shehadeh and Gordon 1969).
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lab7 - CSIRO PUBLISHING Marine Freshwater Research &...

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