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The osmolality and ionic composition of the blood of juvenile Atlantic cod Gadus morhua and their response to conditions of reduced temperature and salinity in summer- and winter-acclimated individuals was investigated. Haematocrit percentage was relatively stable throughout the experimental procedures. Summer-acclimated juvenile Atlantic cod had higher plasma osmolality than winter-acclimated fish in ambient conditions. Plasma Na+ levels were, however, higher in winter conditions, while Cl- did not vary between seasons. Temperature reduction (12, 9 and 6° C in summer and to 6 and 4° C in winter) induced a significant response in plasma osmolality and Na+ levels in summer, but only in Na+ levels in winter-acclimated fish. A pronounced effect was seen in the summer 6°C treatment. Salinity treatments (24, 16 and 8) had a significant effect on almost all the variables in both summer and winter and resulted generally in dilution of ionic and osmotic concentrations of the plasma. This effect was pronounced in the lowest temperature treatments, with the greatest reduction observed in the summer 6°C treatment. This could suggest that winter-acclimated fish are physiologically adapted to cope with lower seawater temperatures as opposed to summer-acclimated fish. [ABSTRACT FROM AUTHOR]

Fish assemblages on two inshore rocky subtidal sites on the west coast of Scotland, were studied using diver visual surveys on a monthly basis between September 1995 and December 1999. A total of 17 689 fishes and 26 species were recorded from the two sites, Saulmore Point (056°27′ N; 005°24′ W) near Oban and Davy''s Rock (055°46′ N; 004°53′ W) on the Isle of Great Cumbrae. The gobiidThorogobius eppiphiatus , dominated the Saulmore Point site; six fish species accounted for >93% of total abundance at that site. At Davy''s Rock four species contributed at least 93% of total fish abundance, and the dominant species was the labrid Ctenolabrus rupestris. Total abundance of the dominant species displayed a clear seasonal trend, and this was significantly related to recorded daily average seawater temperature. A maximum abundance of 4·9 fishes m−2 was recorded in November 1998 at Davy''s Rock and 2·5 fishes m−2 at Saulmore Point in October 1998. Multivariate analysis indicated a degree of variation in assemblage structure between winter and summer at both sites. A number of species showed some degree of interannual variation, in particular the gobiidGobiusculus flavescens whose abundance increased by over 300 times over a 5 month period in 1998. Correlation analysis showed that variation in annual winter seawater temperature could act as an indicator of interannual variation in abundance of some of the dominant species utilizing rocky subtidal habitats. Copyright 2002 The Fisheries Society of the British Isles. Published by Elsevier Science Ltd. All rights reserved. [Copyright &y& Elsevier]