The upper critical thermal limits for alevins of Arctic charr from a Norwegian lake north of the Arctic circle

Mean values ±95% CL of the upper incipient (T_IL) and ultimate (T_UL) lethal temperatures, determined at five acclimation temperatures ( T_A ), increased for T_IL from 19.2 ± 0.4° C ( T_A 0.5° C) to 21.0 ± 0.4° C ( T_A 20° C), and for T_UL from 22.6 ± 0.1° C ( T_A 0.5° C) to 26.6 ± 0.4° C ( T_A 20° C). Mean values were close to those obtained for Arctic charr alevins from Windermere (north-west England). These comparative data for alevins, and previous data for 0+ year parr, indicate negligible geographical variation in the thermal limits of Arctic charr.     

Thermal resistance and upper lethal temperatures of underyearling Lake Inari Arctic charr

Underyearling Arctic charr were acclimated to six temperatures between 6 and 21·5°C and thermal tolerance and resistance were tested after an acclimation period of at least 2 weeks. Resistance times were influenced by acclimation temperature and the highest upper incipient lethal temperature was 23–24°C. An upper limit for cultivation of Lake Inari charr is suggested to be 21°C which is the intercept of the function which represents the upper limit of the thermal tolerance zone.     

Tolerance and resistance to thermal stress in juvenile Atlantic salmon, Salmo salar

SUMMARY. 1. The chief objective was to construct a thermal tolerance polygon for juvenile Atlantic salmon, Salmo salar L., using fish from four groups and two populations: two age groups from one population (0+, 1+ parr from River Leven), two size groups from the other population (slow and Fast growing 1+ parr from River Lune). 2. Fish were acclimated to constant temperatures of 5, 10, 15, 20, 25 and 27°C; then the temperature was raised or lowered at 1°C h^?1 to determine the upper and lower limits for feeding and survival over 10 min, 100 min, 1000 min and 7 days. As they were not significantly different between the four groups of fish, values at each acclimation temperature were pooled to provide arithmetic means (with SE) for the thermal tolerance polygon. 3. Incipient lethal levels (survival over 7 days) defined a tolerance zone within which salmon lived for a considerable time; upper mean incipient values increased with increasing acclimation temperature to reach a maximum of 27.8±0.2°C, lower mean incipient values were below 0°C and were therefore undetermined at acclimation temperatures <20°C but increased at higher acclimation temperatures to 2.2±0.4°C. Resistance to thermal stress outside the tolerance zone was a function of time; the ultimate lethal level (survival for 10 min) increased with acclimation temperature to a maximum of 33°C whilst the minimum value remained close to 0°C. Temperature limits for feeding increased slightly with acclimation temperature to upper and lower mean values of 22.5±0.3°C and 7.0±0.3°C. 4. In spite of different methodologies, values in the present investigation are similar to those obtained in previous, less comprehensive studies in the laboratory. They also agree with field observations on the temperature limits for feeding and survival. Thermal tolerance polygons are now available for eight species of salmonids and show that the highest temperature limits for feeding and survival are those recorded for juvenile Atlantic salmon.     

Thermal tolerance of a northern population of striped bass Morone saxatilis

Thermal tolerance of age 0+ year Shubenacadie River (Nova Scotia, Canada) striped bass Morone saxatilis juveniles (mean ± s . e . fork length, L _F, 19·2 ± 0·2 cm) acclimated in fresh water to six temperatures from 5 to 30° C was measured by both the incipient lethal technique (72 h assay), and the critical thermal method ( C _m). The lower incipient lethal temperature ranged from 2·4 to 11·3° C, and the upper incipient lethal temperature ( I _U) from 24·4 to 33·9° C. The area of thermal tolerance was 618° C². In a separate experiment, the I _U of large age 2+ year fish (34·4 ± 0·5 cm L _F) was 1·2 and 0·6° C lower ( P < 0·01) than smaller age 1+ year fish (21·8 ± 0·5 cm L _F) at acclimation temperatures of 16 and 23° C. Using the C _m, loss of equilibrium occurred at 27·4–37·7° C, loss of righting response at 28·1–38·4° C and onset of spasms at 28·5–38·8° C, depending on acclimation temperature. The linear regression slopes for these three responses were statistically similar (0·41; P > 0·05), but the intercepts differed (25·3, 26·0 and 26·5° C; P < 0·01). The thermal tolerance of this northern population appears to be broader than southern populations.     

Upper thermal limits for feeding and growth of 0+ Arctic charr

When Arctic charr Salvelinus alpinus from two diVerent stocks were fed live Neomysis integer , the upper thermal limits for feeding and growth were established in the range 21·5–21·8° C. These critical temperatures might have been underestimates, because fish tend to show increased sensitivity to handling at high experimental temperatures. In the second experiment, the proportion of feeding undisturbed charr from four stocks decreased initially as temperature was raised in steps from 18 to 22° C. At the lower temperatures, 18 and 20) C, almost all fish resumed feeding, but the recovery time was longer and more fish ceased to feed at 20) C than at 18° C. When the temperature was increased to 21° C, 50% of the fish ceased feeding permanently, and all fish ceased feeding within 2 days at 22° C. It is concluded that 0+ charr cease to feed and grow at c .21·5) C and that the critical temperatures for feeding and growth coincide.     

The critical thermal limits for the stone loach, Noemacheilus barbatulus, from three populations in north-west England

1. The chief objective was to determine the upper and lower thermal limits for feeding and survival in the stone loach, Noemacheilus barbatulus, using juveniles (total length 30–45 mm, live weight 0.25–0.80 g) from one population and adults (total length 77–100 mm, live weight 3.6–7.9 g) from three populations. 2. Fish were acclimatized to constant temperatures of 3, 7, 10, 15, 20, 25 and 27°C; then the temperature was changed at a rate of 1°C/30min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1°C/30min was the optimum value from preliminary experiments, using nine rates from 0.5°C/48h to 18°Ch^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values of 28.0 ± 0.15°C and 5.1 ± 0.55°C for adults, 25.0 ± 0.54°C and 6.1 ± 0.92°C for juveniles. Incipient lethal levels defined a tolerance zone within which stone loach survive for a considerable time; upper limits increased with acclimation temperature to reach a maximum plateau of 29.1 ± 0.18°C for adults and 29.0 ± 0.40°C for juveniles; lower limits also increased from near 0°C to 3.0 ± 0.40°C for adults and juveniles. Upper limits for the ultimate lethal level increased with acclimation temperature to a maximum plateau of 33.5°C for adults (95% CL ± 0.19) and juveniles (95% CL ± 0.40), whilst the lower limits increased from near 0°C to 2.5 ± 0.30°C. At acclimation temperatures below 20°C, upper incipient and ultimate lethal values were significantly lower for juveniles than those for adults. 4. The thermal tolerance of stone loach was higher than that of juvenile Atlantic salmon or brown trout, one or both of these species often being dominant in streams with stone loach.     

The critical thermal limits for the bullhead, Cottus gobio, from three populations in north-west England

1. The objective was to determine the thermal limits for feeding and survival in the bullhead, Cottus gobio, using juveniles (total length 20–30 mm, live weight 0.5–1.5 g) from one population and adults (50–70 mm, 3.5–5.5 g) from three populations. 2. Fish were acclimated to constant temperatures (3, 7, 10, 15, 20, 25 or 27 °C) and the temperature was then changed at a rate of 1 °C /30 min to determine the critical limits for feeding, survival over 7 days (incipient lethal temperature), or survival for 10 min or less (ultimate lethal temperature). The rate of 1 °C/30 min was the optimum value from preliminary experiments, using nine rates from 0.5 °C/48 h to 18 °C h^?1. As values for adults were not significantly different between populations, they were pooled to provide arithmetic means (with 95% CL) for the thermal limits at each acclimation temperature. 3. Feeding limits increased with acclimation temperature to upper and lower mean values (± 95% CL) of 26.5 ± 0.16 °C and 4.2 ± 0.20 °C for adults, 26.6 ± 0.59 °C and 5.0 ± 0.55 °C for juveniles. Incipient lethal levels defined a tolerance zone within which fish survive indefinitely; upper limits increased with acclimation temperature to a plateau of 27.6 ± 0.22 °C for adults and 27.5 ± 0.47 °C for juveniles, lower limits increased from near 0 °C to 2.5 ± 0.31 °C for adults and 2.7 ± 0.47 °C for juveniles. Ultimate lethal levels increased with acclimation temperature to a plateau of 32.5 ± 0.24 °C for adults and 32.6 ± 0.46 °C for juveniles, whilst the lower limits increased from near 0 to 0.9 ± 0.29 °C. Upper feeding, incipient and ultimate lethal values were significantly lower for juveniles than those for adults at acclimation temperatures < 20, < 20 and < 15 °C, respectively. 4. The thermal tolerance of bullheads was slightly lower than that of stone loach, similar to that of juvenile Atlantic salmon and higher than that of brown trout; the thermal limits for feeding were much wider than those for salmon or trout.     

Tolerance of parr of Arctic charr, Salvelinus alpinus, to reduced dissolved oxygen concentrations

One year old pan Item Windermere (north west England) tolerated lower incipient lethal levels of oxygen [18 20 mg 1 ¹: 15 17% air saturation value (ASV)] at lower (5, 10°C) than at higher (15, 20°C) an elimation temperatures (2·2 2·4 mg 1 ¹ 22 25% ASV). Values were not significantly different for two races of charr in the lake and are amongst the lowest recorded for salmenid species.     

Quantification of the Role of Acclimation Temperature in Temperature Tolerance of Fishes

The relative effect of acclimation temperature on temperature tolerance was estimated from a geometrical partitioning of the temperature tolerance polygon of a fish species into three distinct zones relative to four key tolerance temperatures. This approach yields a middle tolerance zone which is independent of acclimation temperature bounded by upper and lower acclimation dependent zones. Acclimation dependent and independent temperature tolerance zones can be quantified by either areal or linear methods. Both methods were applied to quantify the effect of acclimation temperature in 21 species of temperate fishes for which temperature tolerance polygons were available. Temperature tolerance polygon areas of these 21 species ranged from 468 to 1380°C² and are linearly related (r ²=0.93, p<0.001) to ultimate incipient upper lethal temperatures. Although areal and linear partitioning methods yielded similar acclimation independent and dependent tolerances, estimates from the areal method incorporates additional information concerning the shape of the temperature tolerance polygon, in particular lower and upper lethal temperature plateaus. Mean combined acclimation dependent and independent tolerance areas of these 21 species were not different, indicating that acclimation effectively doubles the temperature tolerance polygon. Mean lower acclimation dependent area was nearly three times greater than mean upper acclimation dependent area, suggesting that acclimation plays a larger role in tolerance of low rather than high temperatures. Among these 21 species, temperature tolerance of brook charr and sheepshead minnow were the least and most affected by acclimation temperature, respectively.     

Pools as refugia for brown trout during two summer droughts: trout responses to thermal and oxygen stress

In non–drought years (1977, 1985), temperatures and oxygen concentrations from 1 to 14 July at the deepest point in each of five pools in Wilfin Beck were similar with ranges of 12–18° C and 7·8–9·8 mg l^–1. Trout Salmo trutta were present in all pools. In drought years (1976, 1983), temperature increased and oxygen concentration decreased as pool size decreased. In the two smallest pools, they were outside the thermal and oxygen limits for trout (ranges for both pools 24–29° C, 1·2–2·5 mg l^–1), and trout were absent. Values in a medium–sized pool were close to the incipient lethal levels and a few juvenile trout were present in both drought years. The lowest temperatures and highest oxygen concentrations were recorded in the two largest pools (ranges 20–25° C, 3·6–4·8 mg l^–1) and trout of all ages (0+ to adults) were present in both drought years. In these two pools, both temperature and oxygen concentration decreased from the surface to the deepest point in the pool. Trout preferred lower temperatures near the pool bottom rather than higher oxygen concentrations near the surface, but some fish moved towards the surface at night when the pool cooled slightly. These field results were discussed in relation to lethal values recorded for brown trout in the laboratory, and there was general agreement between field and laboratory values. Trout in the drought years occurred at temperatures close to, or below, the incipient lethal value of 24·7° C (+0·5) and also at the highest oxygen concentrations, but only when these were at temperatures below the incipient lethal value.     

Temperature and salinity tolerances of larval Californian grunion, Leuresthes tenuis (Ayres): A comparison with gulf grunion, L. Sardina (Jenkins & Evermann)

Temperature and salinity tolerances were determined for larval California grunion, Leuresthes tenuis (Ayres), and compared with previous data for Gulf of California grunion, L. sardina (Jenkins & Evermann). Larvae of similar age and acclimation history showed little interspecific difference in thermal tolerance, as measured by half-hour LT₅₀ values for 20–30 day old late postlarvae acclimated at various temperatures, and by upper and lower incipient lethal temperatures for 18°C-acclimated prolarvae. The upper incipient lethal temperature differed by 1 deg.-C (32°C for L. tenuis, 31°C for L. sardina), while the lower incipient lethal temperature for the 18°C acclimated prolarvae of both species was 7.5°C. L. tenuis larvae were much less euryhaline than L. sardina, with incipient lethal salinities of 4.2–41 %. for prolarvae and 8.6–38 %. for 20-day-old postlarvae; comparable values for L. sardina are 4–67.5 %. and 5–57.5 %. Both species show a decrease in temperature and salinity tolerance with age. The larvae of these disjunct congeners show a significant physiological divergence in euryhalinity but not in overall temperature tolerance. These tolerances are discussed in relation to the respective geographic ranges and behavioral responses of the two species.     

Seawater tolerance in captive high-Arctic Svalbard charr (Salvelinus alpinus): effect of photoperiod and body size

Anadromous Arctic charr (Salvelinus alpinus) returning after spending summer at sea were captured in a fish trap in the Dieset River on Spitsbergen (79°10'N), Svalbard. Fish selected for breeding were transported to Trondheim in mainland Norway. Eggs obtained from the charr were fertilized and incubated in total darkness. First-fed alevins and resulting parr were kept under continuous light until an age of 0+ and 1+ years, respectively. Some 1+ charr were kept as controls under a continuous short-day photoperiod (6L:18D) from autumn until the end of the experiment the following July. Charr aged 0+ and 1+ years old were exposed to a short-day photoperiod from October until January and a simulated natural photoperiod for 80°N from January until the end of the experiments. Challenge tests demonstrated a size-dependent seawater tolerance for charr with a body length less than 18 cm. Fish smaller than 12 cm did not survive the 96-h test period. The larger charr kept under simulated natural photoperiod developed increased hypoosmoregulatory capacity. Charr kept under short-day treatment showed a slight, short-lived increase in seawater tolerance. A 7-days seawater challenge test at the end of the experiment (July) demonstrated that the anticipatory seawater preparation in charr is influenced by photoperiod. We conclude that offspring from anadromous high-Arctic charr must achieve a threshold body size (>25 cm) before they can respond to photoperiod signals which trigger the development of the hypoosmoregulatory capacity typical for smoltifying salmonids.     

Growth and food consumption of 0+ Arctic charr fed pelleted or natural food at six different temperatures

The effects of temperature and diet on the specific growth rate and food consumption of 1-summer-old Arctic charr Salvelinus alpinus were studied. Fish were reared singly in aquaria at six different constant temperatures (5, 9, 13, 16, 18 and 20°C). They were fed Neomysis integer or commercial pelleted food for 2 weeks and growth and food consumption were measured. In both experiments, growth rate increased to an optimum at 15°C. Growth rates were high in the range 13–18°C, with no significant ( P >0·05) differences between temperatures. No significant ( P> 0·05) differences in growth were found between fish at 9 and 20°C. There were no effects of diet on size-adjusted growth rates. The growth efficiency decreased with increasing temperature in both treatments, but the decrease was faster in the Neomysis treatment. Charr seemed to compensate for the high water content (79·5%) of Neomysis by having a higher food intake.     

Comparative developmental biology of pink salmon, Oncorhynchus gorbuscha, in southern British Columbia

Eggs and alevins from 21 families of pink salmon, Oncorhynchus gorbuscha , from five odd-year broodline stocks spawning in southern British Columbia were incubated under controlled water temperatures of 4° C, 8° C and 12° C. There were significant differences in egg survival among stocks and among families within stocks at all incubation temperatures, but the differences were greatest at 4° C. Alevin survival was at least 97% for each stock at each temperature. The most northern spawning stocks had higher egg survival at 4° C than did the others. Hatching time of the alevins and emergence time of the fry were similar for all five stocks. Alevins hatching at 8° C were longer than those hatching at 4°C or 12°C, but there were no stock differences in alevin length or tissue weight. Stocks with larger eggs produced alevins of greater total weight and more yolk. Emergent fry from Vancouver Island stocks had the greatest tissue weight at 12° C, but Fraser River fry were heaviest at 8° C. There were significant differences among families within stocks for alevin and fry size parameters, suggesting that family variation should be accounted for in studies of salmonid developmental biology.     

Lethal temperature of marine fishes of the Gulf of Thailand

Twenty four marine fish species of the Gulf of Thailand were studied. The results suggested that increased acclimation temperature resulted in increased mean avoidance temperature (AT), critical thermal maximum (CTM) and upper incipient lethal temperature (UILT). At the acclimation temperature, which is normally the ambient seawater temperature of the Gulf of Thailand (28° C), the upper incipient lethal temperature ranged from 34° C to 37–5° C. Monocanthus chinensis and Cynoglosus puncticeps had the lowest thermal resistance. Mugil dussumerii, Therapon theraps and Scatophagus argus the highest and the rest in the middle range.     

Seasonal changes in fast-starts in the short-horn sculpin: integration of swimming behaviour and muscle performance

In short-horn sculpin Myoxocephalus scorpius , the power requirements for fast-start swimming and the length-specific velocity of the curvature wave travelling down the spine ( Û ) were not influenced significantly by acclimation to summer and winter conditions at test temperatures of 5 and 15° C. However, in-vivo and in-vitro muscle performance exhibited acclimation responses at 15° C. Seasonal acclimation altered the escape performance curves for power and Û significantly over a wider temperature range of 0·8–20° C. Û was significantly higher at 20° C in the summer- than winter-acclimation group. The acclimation of lower levels of physiological organization at 15° C may thus serve to extend the thermal limits for escape performance in summer acclimated fish.     

Observations on growth rates of Arctic charr, Salvelinus alpinus (L.), reared at low temperature

Food intake and growth of Arctic charr, Salvelinus alpinus , in fresh water was studied at three temperatures 2·9, 8·4 and 13·1° C). Best growth and highest food intake occurred at 13·1°C. The approximate chemical composition was dependent upon rearing temperature, fish reared at the highest temperature depositing large quantities of fat. Fish were later grown on in either fresh or salt water where two growth patterns were observed. In the light of published data for Salvelinus spp., it is suggested that the poorest growth was shown by fish which were incapable of complete adaptation to saltwater conditions.     

The influence of thermal parameters on the acclimation responses of pinfish Lagodon rhomboides exposed to static and decreasing low temperatures

Pinfish Lagodon rhomboides acclimation rates were determined by modelling changes in critical thermal minimum ( T _{crit min}, ° C) estimates at set intervals following a temperature decrease of 3–4° C. The results showed that pinfish gained a total of 3·7° C of cold tolerance over a range of acclimation temperatures ( T _acc, ° C) from (23–12° C), that cold tolerance increased with exposure time to the reduced temperature at all T _acc, but that the rate of cold tolerance accruement (mean 0·14° C day⁻¹) was independent of T _acc. A highly significant ( P < 0·001) multivariate predictive model was generated that described the acclimation rates and thermal tolerance of pinfish exposed to reduction in water temperature: log₁₀ T _{crit min}= 0·41597 − 0·01704 T _acc+ 0·04320 T _plunge− 0·08376[log₁₀ ( t + 1)], where T _plunge is plunge temperature (° C) and t is the time (days). A comparison of the present data, with acclimation rate data for other species, suggests that factors such as latitude or geographic range may play a more important role than ambient temperature in determining cold acclimation rates in fishes.     

Temperature requirements of Atlantic salmon Salmo salar, brown trout Salmo trutta and Arctic charr Salvelinus alpinus: predicting the effects of climate change

Atlantic salmon Salmo salar, brown trout Salmo trutta (including the anadromous form, sea trout) and Arctic charr Salvelinus alpinus (including anadromous fish) provide important commercial and sports fisheries in Western Europe. As water temperature increases as a result of climate change, quantitative information on the thermal requirements of these three species is essential so that potential problems can be anticipated by those responsible for the conservation and sustainable management of the fisheries and the maintenance of biodiversity in freshwater ecosystems. Part I compares the temperature limits for survival, feeding and growth. Salmo salar has the highest temperature tolerance, followed by S. trutta and finally S. alpinus. For all three species, the temperature tolerance for alevins is slightly lower than that for parr and smolts, and the eggs have the lowest tolerance; this being the most vulnerable life stage to any temperature increase, especially for eggs of S. alpinus in shallow water. There was little evidence to support local thermal adaptation, except in very cold rivers (mean annual temperature <6·5° C). Part II illustrates the importance of developing predictive models, using data from a long-term study (1967-2000) of a juvenile anadromous S. trutta population. Individual-based models predicted the emergence period for the fry. Mean values over 34 years revealed a large variation in the timing of emergence with c. 2 months between extreme values. The emergence time correlated significantly with the North Atlantic Oscillation Index, indicating that interannual variations in emergence were linked to more general changes in climate. Mean stream temperatures increased significantly in winter and spring at a rate of 0·37° C per decade, but not in summer and autumn, and led to an increase in the mean mass of pre-smolts. A growth model for S. trutta was validated by growth data from the long-term study and predicted growth under possible future conditions. Small increases (<2·5° C) in winter and spring would be beneficial for growth with 1 year-old smolts being more common. Water temperatures would have to increase by c. 4° C in winter and spring, and 3° C in summer and autumn before they had a marked negative effect on trout growth.     

The effect of temperature fluctuations on oxygen consumption and ammonia excretion of underyearling Lake Inari Arctic charr

Underyearling Lake Inari Arctic charr Salvelinus alpinus were acclimated to 11·0) C for 3 weeks, and then one group was maintained at 11·0) C and others were exposed to 14·4) Cconst, 17·7) C_const or a diel fluctuating temperature of 14·3° C ± 1° C (14·3° C_fluc). Routine rates of oxygen consumption and ammonia excretion were measured over 10 days before the temperature change and over 31 days following the change. Measurements were made on fish that were feeding and growing. The temperature increase produced an immediate increase in oxygen consumption. There was then a decline over the next few days, suggesting that thermal acclimation was rapid. For groups exposed to constant temperature there was an increase in oxygen consumption ( M _accl, mg kg⁻¹ h⁻¹) with increasing temperature ( T ), the relationship being approximated by an exponential model: M _accl= 46·53e0·^{086 T} . At 14·3° C_fluc oxygen consumption declined during the 3–4 days following the temperature shift, but remained higher than at 14·4° C_const. This indicates that small temperature fluctuations have some additional influences that increase metabolic rate. Ammonia excretion rates showed diel variations. Excretion was lower at 11° C_const than at other temperatures, and increases in temperature had a significant effect on ammonia excretion rate. Fluctuating (14·3° C_fluc) temperature did not influence ammonia excretion relative to constant temperature (14·4° C_const).