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Notes: The numbers of mucous cells in the epidermis of the head and body and in the surface of the gill arch of the amphibious blenny, Blennius pholis L., were estimated on fish immersed in sea water and after 4 h aerial exposure. During emersion there appeared to be a considerable reduction in the frequency of epithelial mucous cells in the areas studied, although counts for the head epidermis were somewhat variable. A concomitant decline in the number of cells thought to be actively secreting was also recorded in tissue samples from both the head and gills, while in the body epidermis the potential for mucus-secretion was maintained close to the levels observed in immersed fish.Histochemical studies revealed epidermal mucous cells containing either sialylated acid mucopolysaccharides or neutral mucins, or a mixture of these, in both the head and the body, whereas in the gill arch epithelia there were, in addition, cells containing sulphated acid mucopolysaccharides. After emersion, a disproportionate loss of cells containing neutral and sialylated mucus from the gill epithelia resulted in an increase in the proportion of secreting cells staining positively for sulphated acid mucopolysaccharides.The results of this study are discussed in relation to nitrogenous excretion during aerial exposure.

Notes: 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 gobiid Thorogobius 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 gobiid Gobiusculus 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.

Notes: A study of seasonal, locational and sexual variations of growth, diet, somatic condition (Ks), gonadosomatic condition (GSI) and hepatosomatic condition (HSI), of the goldsinny wrasse, Ctenolabrus rupestris, was made on specimens taken from three areas (Millport, Oban and Luing) of the west coast of Scotland from May 1992 to June 1993. Capture throughout the year was by either baited creel or by anaesthetics applied underwater. Male goldsinny of age 1 year and older ranged in total length from 67-155 mm, total weight 3.8-58.8 g, and had a maximum age of 14+ years. Females of 1 year and older ranged in total length from 59-159 mm, total weight 2.4-65.4 g and had a maximum age of 20+ years. Juvenile (0 +) goldsinny were mostly of indeterminate sex, ranged in total length from 16-57 mm, and total weight 0.08-1.97 g. Female growth was slower than that of males for all three locations; growth of male and female goldsinny from Millport was slower than the respective sexes at the other two locations. Length-weight relationships varied with age and location. There were differences in Ks, GSI, HSI and dietary trends associated with variation in season, sex and location. The implications of this variation are discussed in relation to the management of a sustainable goldsinny fishery.

Notes: Fish are totally excluded, by virtue of their physiology, only from a permanently terrestrial existence, from bodies of water with a pH below 4 or above 10 or with a calcium content below 10 mmol l−1, from permanently anoxic environments and from hypersaline water bodies with salinities above about 90‰. In less extreme, but still demanding, environments physiological limitations constrain the distribution of certain categories of fish. Extreme conditions are associated with low-energy life styles.

Notes: A field survey of populations of goldsinny wrasse (Ctenolabms rupestris) was undertaken on selected areas of rocky coast of west Scotland. Observations by sub-aqua diving were used to determine distribution, habitat preference, and population density, and their seasonal variations. Availability of the preferred refuge type (crevices on rock faces, or between boulders, where two or more entrances exist) was essential in determining goldsinny presence. Goldsinny were not always present in areas or at depths where the influences of freshwater runoff (low temperatures and salinities) were likely, even if the preferred habitat type was available. In areas remote from these influences, and where there were suitable refuges, depth of water (0–44 m), macroalgal cover and high current speeds (2.1–3.6 ms−1) did not affect goldsinny distribution. Observed densities of goldsinny reached a peak in summer months with a maximum of 4.0 m−2 in areas of shallow boulder scree, but only 1.0 m−2 in shallow areas with little scree, or at deeper study sites. Numbers of goldsinny observed actively swimming decreased after October, with a rapid disappearance in November. A gradual reappearance was recorded in late April, and early May. Changes in activity may be influenced by both water temperature and photoperiod. Young-of-the-year goldsinny were first observed in August in shallow water (0–8 m) areas typified by rock/boulder scree and/or high macroalgal cover. Where adults also inhabited these nursery areas, 0+ fish could make up over 50% of the total population. After their first winter, juvenile goldsinny may migrate away from inshore sites.

Notes: Yolk-sac fry of brown trout were exposed to three levels of single trace metals (Cu, 20,40,80 nmol 1-1; Pb, 12·5,25,50 nmol 1-1; Zn, 75,150,300 nmol 1-1) typical of concentrations reported for acid soft waters, in flowing, artificial, soft water media maintained at pH 4·5 and [Ca] of 20 or 200 μmol 1-1for 30 days.Mortalities were high in fry subjected to all levels of the three trace metals at [Ca] 20 μmol 1-1, with 80% of the total deaths occurring between days 11 and 15 of the experiment. 25% mortality occurred at low [Ca] and pH 4·5 in the absence of trace metals, with only one death recorded at [Ca] 200 μmol1-1’(Cu, 80 nmol 1-1). At high [Ca] all three levels of Cu and Pb impaired net Na and K uptake; Cu was the only metal to reduce the uptake of Ca. The Zn treatments had no significant effect on mineral uptake. Calcification of centra was reduced by all three Cu treatments at [Ca] 200 μmol 1-1. The lowest Zn concentration (75 nmol 1-1) was the only other treatment to impair skeletal development. In the absence of trace metals, low [Ca] significantly reduced Ca, Na and K uptake, skeletal calcification and dry mass at pH 4·5.The deleterious effects of low Cu, Pb and Zn concentrations at low pH and low [Ca], and the ameliorative effect of higher ambient [Ca], are discussed in relation to fishery status in soft, acid waters.

Notes: Wrasse used as cleaner fish with farmed Atlantic salmon Salmo salar can be subjected to large and rapid temperature and salinity fluctuations in late autumn and early winter, when summer-warmed surface water is affected by early snowmelt episodes. Because of their containment in sea cages, wrasse which are essentially acclimated to summer temperatures may be rapidly exposed to winter conditions. Short-term tolerance of low temperature and low salinity by three species of wrasse, goldsinny Ctenolabrus rupestris rock cook Centrolabrus exoletus corkwing Crenilabrus melops caught during the summer, and winter-caught corkwing, was investigated. A 3–day period at 30 or 32‰ salinity and temperature 8, 6 or 4° C (for summer-caught fish; 4° C only for winter-caught) was followed by a decline in salinity to 24, 16 or 8‰ over c. 36 h, followed by a further 24 h at these salinities held constant, at each of the three temperatures. Controls in 30 or 32‰ were maintained at 8, 6 or 4° C. Mortality of summer-caught corkwing and rock cook was high at 4° C, whereas the influence of salinity on mortality was small. Mortality of goldsinny was low or zero in all treatments. Surviving corkwing and rock cook after 3 days at 4° C and 32‰ salinity had elevated plasma osmolality: in summer-caught corkwing, plasma [Cl°] and [Na+] were high, whereas in rock cook only [Na+] was high. Haematocrit was low in summer-caught corkwing, high in rock cook. In survivors of all three species at the end of the experiment, values of all these parameters were comparable with those of fish at the beginning of the experiment, except that survivors at low salinity (8, 16‰) had low plasma osmolality, at all temperatures, and in surviving rock cook in these treatments haematocrit was high and plasma [Cl−] was low. Winter-caught corkwing had higher osmolality, [Na+] and [Cl−] than summer-caught corkwing; there was no difference in haematocrit. Survival of wintercaught corkwing exposed to four salinities at 4° C was much higher than that of summercaught corkwing under the same conditions. Little change in blood physiology was recorded for winter-caught corkwing, with only fish subjected to 8‰ and 4° C showing signs of osmoregulatory stress. The interspecific and seasonal differences in survival and blood physiology at low temperature and low salinity are discussed in relation to wrasse survival over winter, both in the field and in salmon farms.

Notes: 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.

Notes: Summary Amphibious behaviour in fish has evolved separately many times since the first amphibious fishes, the rhipidistian crossopterygians, ventured onto land about 350 million years ago. This behaviour has resulted in the colonization and eventual domination by vertebrates of the terrestrial habitat. It is generally proposed that aquatic hypoxia, owing to metabolic oxygen consumption and organic decay, was the most important selective force in the evolution of air-breathing vertebrates (e.g. Randall et al., 1981). Modern amphibious fish species give an insight into the reasons for leaving and eventually abandoning the aquatic habitat. Amphibious fishes today leave the water for a variety of reasons associated with degradation of their aquatic habitat, or biotic factors within it. The possible causal factors which may elicit an emergence response are summarized in Fig. 1(a) and (b). Amphibious fish inhabiting closed systems, as typified by freshwater or intertidal pools, may leave water for any of the reasons detailed in Fig. 1(a). The relative importance of any one stimulus is likely to vary between different species. However, it is possible that in closed systems, adverse fluctuations in physico-chemical parameters will have a more important effect in eliciting amphibious behaviour than will biotic factors. In open systems, such as coastal waters or large freshwater bodies, effectively two routes of escape from adverse aquatic conditions are available to amphibious fish. They may move onto land, or alternatively they may move underwater to find better conditions. In such a system, where physico-chemical parameters remain relatively constant, abiotic factors are unlikely to have a significant influence on amphibious behaviour. The dominant stimulus in open systems is possibly the three-way interaction between predation, competition, and short-or long-term food availability (Fig. 1(b)). It is unlikely that any one of the factors discussed in this review will act alone in causing amphibious behaviour, and in this respect the available literature on fish leaving water is lacking. Much of it is fragmentary and partly anecdotal, and the limited amount of experimental work tends to concentrate on individual causal factors. There is evidently scope for detailed examination of emersion in a number of amphibious fishes, testing a matrix of environmental and biotic stimuli, in an attempt to determine in more detail the reasons for such behaviour.

Notes: Summary Over the last 20–30 years there has been a very extensive international research effort into freshwater acidification and the decline or loss of soft-water fisheries. The research includes many laboratory studies on physiology and survival of fish under the conditions caused by acidification. The causes of acidification have become increasingly well understood and accepted. In many countries, industrial and environmental management strategies are being implemented with the eventual aim of halting or reversing acidification in vulnerable areas. Attention has shifted away from research into the effects of acidification on fish, and the number of new papers on this subject is declining. Now appears a good time to review this research. As is often the case in research of this kind, it is difficult to compare work from different laboratories. Especially in earlier work, experimental conditions may not be fully relevant to the field (e.g. in the choice of ambient calcium concentration), experimental media may be inadequately specified (e.g. trace metal concentrations) and analytical techniques may be open to question (e.g. pH measurement). This may explain, in part, why agreement is lacking on many aspects of the physiological effects on the early life stages of fish, as well as the adult stages to some extent. If research is to continue in this field, then adoption of standard soft, acid water media would be of significant benefit. Nethertheless, some very general conclusions on fish early life stages can be reached. There is some evidence of impaired gametogenesis and spawning, but in this area there is still a need for systematic research. After fertilization, the chorionic membranes afford protection from the effects of low pH and especially the accompanying toxic trace metals, notably aluminium. Indeed, dissolved aluminium can ameliorate acid toxicity at this stage in development, possibly by helping to decrease membrane permeability and reduce H+ uptake. The main hazard seems to be impaired development (perhaps related to a decline in pH of the perivitelline fluid), often leading to a lack of ability to escape from the chorionic membranes on hatching. After hatching, vulnerability increases. Dissolved aluminium, and other trace metals associated with acidification, become more important. Some studies indicate continuing protection from low pH afforded by low concentrations of aluminium. The causes of death can still only be inferred: much attention has concentrated on mineral uptake and balance, and there is anecdotal evidence of respiratory impairment, although not as unequivocal as it is for postlarval fish. Comparison with the physiological effects on postlarval fish is not necessarily helpful. There seems to be at least one important difference. Unlike postlarvel fish, larvae do not find aluminium at around pH 5.5 (when respiratory effects are probably most important) the most hazardous combination; rather, the greatest danger to larvae seems to be when very low pH (〈5.0) and trace metals (including aluminium) combine in some kind of joint toxic effect. There is a great increase in vulnerability once dependence on the yolk has come to an end. This period coincides with the movement from the incubation site in the substratum into the open water, where the relevant water chemistry is likely to fluctuate between greater extremes. However, it is earlier, during autumn rainstorms and spring snowmelt, that pH and concentrations of protective calcium ions usually reach their lowest and metals like aluminium their highest values. In waters where acidification is most likely to occur, the early life stages of many freshwater fish species will be close to their survival threshold and only a slight decline in water quality might result in the loss of a complete year class, which would affect recruitment and eventual population status. With gradual acceptance of the causes and effects of freshwater acidification, the research effort in relation to fish is declining or shifting towards attempts to re-establish fisheries in vulnerable areas. As outlined above, only very general conclusions can be reached on individual life stages, and the relative susceptibilities compared. However, in many respects the sequence of events in the loss of fisheries is not fully understood, and information is lacking on how events at significant stages of the life cycle affect subsequent survival, development and recruitment. Plenty of work is still required.