Compensation limits of fish muscle myofibrillar ATPase enzyme to environmental temperature

1. 1.|Goldfish acclimated to a range of temperatures between 5 and 35°C were found to only compensate the specific activity of their myofibrillar ATPase enzyme between 10 and 30°C.

2. 2.|The preferred temperatures of goldfish acclimated to 5°C and to 30°C were determined to be about 10 and 26°C respectively.

3. 3.|It is conlcuded that goldfish are only able to acclimate their myofibrillar ATPase system to temperatures between 10 and 30°C, but acclimation to these temperatures enables them to tolerate extremes.

Thermal responses of juvenile squaretail mullet (Liza vaigiensis) and juvenile crescent terapon (Terapon jarbua) acclimated at near-lethal temperatures, and the implications for climate change

The negative effects of climate alteration on coral reef fishes receive ever increasing attention; however, implications of rising sea temperatures on fishes inhabiting marine nursery environments are poorly understood. We used critical thermal methodology to quantify critical thermal maxima (CTmaxima) of juvenile squaretail mullet (Liza vaigiensis) and juvenile crescent terapon (Terapon jarbua) captured from shallow seagrass nursery areas around Hoga Island, southeast Sulawesi, Indonesia. We tested the hypothesis that these distantly related fishes, when acclimated to cycling temperatures, would display higher CTmaxima than groups acclimated at constant temperatures. Groups of mullet acclimated to a constant temperature of 37 °C and temperature cycles of 35 to 39 °C or 37 to 41 °C displayed statistically similar mean CTmaxima of 44.7, 44.4 and 44.8 °C, respectively. Likewise, terapon acclimated at temperature cycles of 37 to 40 °C did not display a higher CTmaxima than fish acclimated at a constant temperature of 37 °C, with both acclimation groups' mean CTmaxima equal to 43.8 °C. Acclimation to higher cycling temperatures did not result in significant upper temperature tolerance acquisition for either species; however, mullet values were significantly higher than those seen in terapon (P < 0.0001). These data suggest that mullet and terapon will not suffer direct thermal effects should shallow nursery temperature increases be marginally higher than 1-2 °C above ~ 27 °C, and they provide evidence that the upper thermal tolerance of fishes inhabiting shallow seagrass and mangrove areas can approach the biokinetic limits for vertebrate life. Tropical marine fishes inhabiting fringing nursery environments may have the upper thermal tolerance necessary to endure substantial increases in sea temperatures.     

Temperature acclimation alters cardiac performance in the lobster Homarus americanus

The American lobster is a poikilotherm that inhabits a marine environment where temperature varies over a 25°C range and depends on the winds, the tides and the seasons. To determine how cardiac performance depends on the water temperature to which the lobsters are acclimated we measured lobster heart rates in vivo. The upper limit for cardiac function in lobsters acclimated to 20°C is approximately 29°C, 5°C warmer than that measured in lobsters acclimated to 4°C. Warm acclimation also slows the lobster heart rate within the temperature range from 4 to 12°C. Both effects are apparent after relatively short periods of warm acclimation (3–14 days). However, warm acclimation impairs cardiac function at cold temperatures: following several hours exposure to frigid (<5°C) temperatures heart rates become slow and arrhythmic in warm acclimated, but not cold acclimated, lobsters. Thus, acclimation temperature determines the thermal limits for cardiac function at both extremes of the 25°C temperature range lobsters inhabit in the wild. These observations suggest that regulation of cardiac thermal tolerance by the prevailing environmental temperature protects against the possibility of cardiac failure due to thermal stress.     

Calcium regulatory proteins and temperature acclimation of actomyosin ATPase from a eurythermal teleost (Carassius auratus L.)

Summary Goldfish (Carassius auratus) were acclimated for 5 months at temperatures of either 2°C or 31°C. Natural actomyosin was prepared from white myotomal muscle and its Mg²⁺Ca²⁺ ATPase activity determined. Temperature acclimation results in adaptations in substrate turnover number and thermodynamic activation parameters of the ATPase. When assayed at 31°C the Mg²⁺Ca²⁺ ATPase of natural actomyosin was 4 times higher in 31°C than 2°C acclimated fish. Arrhenius plots of natural actomyosin ATPase from cold acclimated fish show a break in slope at 15–18°C. In contrast, the temperature dependence of warm acclimated actomyosin was linear. Activation enthalpy (H ) of the ATPase, calculated over the range 0–16°C, was approximately 8,000 cal/mole lower in 2°C than 32°C acclimated fish.In contrast, desensitised actomyosins from which the calcium regulatory proteins have been removed show a linear temperature dependence in the range 0–32°C and have similar properties in 2°C and 31°C acclimated fish. Cross-hybridisation of regulatory proteins (tropomyosin-troponins complex) from cold-acclimated fish to desensitised actomyosin from warm-acclimated fish alters the ATPase towards that of cold-acclimated natural actomyosin and vice versa. The results suggest that the regulatory proteins can influence the kinetics of the ATPase and, furthermore, that they are involved in the acclimation of the actomyosin to different cell temperatures.     

Effect of temperature on osmotic and ionic regulation in goldfish,Carassius auratus L.

Summary Urine flow increased with acute temperature increases and showed temperature acclimation. When measured at 20 °C the urine flow of 10 °C acclimated fish was 3.2 times greater than the urine flow of 30 °C acclimated fish. In fish acclimated to 24 °C renal reabsorption of Na and Cl was independent of temperature over an intermediate range of temperatures (14–24 °C) but near the lower lethal temperature (6.5 °C) renal Na and Cl reabsorption was inhibited. Water permeability of the renal tubules was not affected by acute temperature change between 6.5 and 24 °C. Urine osmolality and urine Na, K and Cl concentrations showed nearly perfect temperature compensation in fish acclimated to 10 °C and 30 °C. The rate of renal excretion of Na and Cl showed temperature acclimation in that Na and Cl ecxretion measured at 20 °C was 7 to 8 times greater in 10 °C acclimated fish than in 30 °C acclimated fish. The rate of excretion of Na and Cl measured at 30 °C in 30 °C acclimated fish was approximately 1.7 times the rate of excretion measured at 10 °C in 10 °C acclimated fish.The branchial uptake of Na, measured in tap water, of fish acclimated to 10, 20 and 30 °C in demineralized water increased with acute increases in temperature. When the three acclimation groups were compared at an intermediate temperature (20 °C), the 10 °C acclimated group showed the highest rate of net uptake, and the 30 °C group the lowest rate of uptake. This apparent temperature acclimation of Na uptake was correlated with differences in the plasma Na concentration of the three acclimation groups. Plasma Cl concentrations were also correlated with acclimation temperature in fish acclimated in demineralized water, but the rate of net Cl uptake was considerably less than that for Na. Sodium and Cl uptake in fish which had been acclimated in tap water was very variable and was not clearly affected by acute changes in temperature. Uptake of Na and Cl by fish held in tap water did not show temperature acclimation. The difference between uptake and excretion of fish acclimated in tap water was not significantly different from zero, indicating that the fish were in salt balance.The study was supported by National Institutes of Health Grant GM 16932-02 to Dr. Bodil Schmidt-Nielsen. I am grateful to Dr. Schmidt-Nielsen for many useful discussions during the course of this work.     

The behavioural thermal preference of the common triplefin (Forsterygion lapillum) tracks aerobic scope optima at the upper thermal limit of its distribution

Ocean temperatures are rising and fish are redistributing themselves poleward and into deeper waters to retain a favourable thermal environment (11 and 30). To investigate whether biogeographical shifts might occur through behavioural redistribution into optimal environments, we examined whether a common triplefin species (Forsterygion lapillum) would behaviourally select (i.e. track) a temperature that matches its physiological optimum under laboratory conditions. F. lapillum were acclimated to 15, 18 or 21 °C for at least 4 weeks, after which various rates of oxygen consumption (MO₂) were measured using automated respirometry and their behavioural thermal preferenda assessed using an electronic shuttle choice tank. Aerobic metabolic scope (resolved as the difference between maximal and maintenance MO₂) did not differ across all thermal treatments (i.e. specimens acclimated to 15, 18 or 21 °C) revealing that F. lapillum is a eurythermal species with a range of optimal physiological performance that closely matches the environmental conditions they are exposed to. A comparably wide range of behavioural preference would perhaps be expected but all three acclimation groups showed a surprisingly narrow behavioural preference range of 20–21 °C. The results therefore suggest that, irrespective of acclimation, eurythermal species may have a tendency to select optimal temperatures at the upper limit of their thermal distribution range. The results are discussed in the context of the ecology and the expected response of F. lapillum to future thermal change.     

Response of juvenile diamond-backed terrapins (Malaclemys terrapin) to an aquatic thermal gradient

In many ectotherms, selection of environmental thermal niches may positively affect growth, nutrient assimilation rates, immune system function, and ultimately survival. Temperature preference in some turtle species may be influenced by environmental conditions, including acclimation temperature. We tested for effects of acclimation temperature (22 °C, 27 °C) on the selected temperature and movement patterns of 14 juvenile Malaclemys terrapin (Reptilia: Emydidae) in an aquatic thermal gradient of 14–34 °C and in single-temperature (22 °C, 27 °C) control tests. Among 8–10 month old terrapins, acclimation temperature influenced activity and movement patterns but did not affect temperature selection. In thermal gradient and single-temperature control tests, turtles acclimated to 27 °C used more tank chambers and relocated between chambers significantly more frequently than individuals acclimated to 22 °C. However, acclimation temperature did not affect temperature selection: both 22- and 27 °C-acclimated turtles selected the warmest temperature (34 °C), and avoided the other temperatures available, during thermal gradient tests. These results suggest that young M. terrapin are capable of detecting small temperature increments and prefer warm temperatures that may positively influence growth and metabolism.     

Thermal tolerance and cold hardiness strategy of the sub-Antarctic psocid <Emphasis Type="Italic">Antarctopsocus jeanneli</Emphasis> Badonnel

Despite considerable work on the upper and lower lethal limits of insects, several major taxa have received little attention. We investigated the lower and upper thermal tolerances and cold hardiness strategy of Antarctopsocus jeanneli Badonnel (Psocoptera: Elipsocidae) from sub-Antarctic Marion Island. A. jeanneli is freeze intolerant and, more specifically, moderately chill tolerant. Field fresh A. jeanneli had a mean supercooling point (SCP) of –11.1°C, whereas LT50 was –7.7°C, indicating pre-freeze mortality. A. jeanneli responds to acclimation: mean SCP increased from –15.8°C at a treatment temperature of 0 to –7.3°C at 15°C, as a result of a shift in the proportion of individuals in the high and low groups of the bimodal SCP distribution. A. jeanneli has upper thermal tolerances that are lower than those of other insect species on Marion Island, but within the range of expected microhabitat temperatures. Further study will establish whether freeze intolerance is characteristic of Psocoptera.     

Effects of acclimation and acute temperature change on specific dynamic action and gastric processing in the green shore crab, Carcinus maenas

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10 °C or 20 °C and subsequently exposed to treatment temperatures of 5, 15, or 25 °C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10 °C acclimated group exposed to acute test temperatures. The Q₁₀ values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20 °C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20 °C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20 °C acclimated crabs, with the highest value measured at the treatment temperature of 15 °C. The decline in total SDA after acute exposure to 5 and 25 °C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20 °C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10 °C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones.     

Critical thermal maxima and acclimation rate of the tropical guppy Poecilla reticulata

Tropical guppies, Poecilia reticulata, collected from the canal of La Laguna Los Patos were acclimated over a four-week period at local water temperatures of 24–33 °C to determine their critical thermal maxima (CTM) and death points (DP), as criteria of thermal tolerance. In addition, individual thermal tolerance times at a lethal temperature of 38.5 °C were measured over 12 days for upward acclimation from 24 to 30 °C and over 16 days for downward acclimation from 30 to 24 °C to determine acclimation rate just before and after changing the acclimation temperatures. The CTM ranged from 38.95 to 40.61 °C and the average DP varied from 41.22 to 42.86 °C. Positive relationships were apparent between thermal tolerance and acclimation temperatures, and thus heat tolerance criteria (CTM and DP) were significantly different among acclimation temperatures. Individual heat tolerance times increased most rapidly during the first 6 hours of upward acclimation after transfer from 24 to 30 °C, continued to increase another 5 days and fluctuated after initial acclimation was completed. The heat tolerance times of fish transferred from 30 to 24 °C declined steadily over times, reaching a minimum at 14–16 days after transfer.     

Heat Resistance and Thermal Acclimation Rate in Tropical Tetra <Emphasis Type="Italic">Astyanax bimaculatus</Emphasis> of Venezuela

Venezuelan river tetra, Astyanax bimaculatus juveniles of 34.1–36.7mm standard length and 0.83–1.0g wet weight were acclimated for four weeks to 24–33°C, which are approximate average minimum and maximum river temperatures throughout the year. The fish acclimated to 24, 27, 30, and 33°C were exposed for 10000 minutes at 35, 36, 37, 38, and 39°C to determine individual heat resistance times. To determine acclimation rates, the juveniles acclimated to 24 and 30°C were tested for individual heat resistance times at 39°C by changing acclimation temperatures. The individual heat resistance times were increased in accordance with an increase in acclimation temperature and a decrease in test temperature, indicating that acclimation level has a great influence on thermal resistance of the fish tested. As the fish were transferred from 24 to 30°C (upward acclimation), they completed their acclimation level in a few days, while those transferred from 30 to 24°C (downward acclimation) required about 14 days. It has reaffirmed the following general behavior: the rate of gain in thermal resistance is fast and the loss in heat tolerance is very slow. This physiological phenomenon is very important for tropical fish, which acclimates rapidly in rising temperature during the hot day and does not lose this level in decreasing temperature during the cool night. Consequently, a tropical fish can maintain its maximum resistance level, adapt well in thermally fluctuating tropical waters, and survive in lethally high temperatures caused by a sudden increase in temperature during hot day.     

Thermal acclimation capacity of Jack Beardsley mealybug (Pseudococcus jackbeardsleyi) to survive in a warming world

The study of thermal tolerance and acclimation capacity in Jack Beardsley mealybug, Pseudococcus jackbeardsleyi Gimpel and Miller is the crucial step in determining their abilities to cope with climate change. Thus, the aim of this research was to determine the effects of acclimation temperatures on the changes in thermal tolerance of P. jackbeardsleyi. The influences of acclimation temperature at moderate (25?°C) and high (35?°C) temperatures on their lower and upper thermal limits were measured composed of critical thermal minimum (CT_min), maximum (CT_max), chill coma temperature (CCT) and heat coma temperature (HCT) for first instar nymphs and adults. The important information derived from this study revealed that the upper thermal limits of adults are constrained to a relative narrow range that will make them sensitive to relative small changes in temperatures, whilst all mean upper thermal indices at 35?°C were significantly higher than at 25?°C for nymphs. For this highlight notice, nymphs have more potential to change their upper thermal limits which will allow them to withstand high temperatures in the field. These results are a sign to warn us that P. jackbeardsleyi could become highly noxious which cause severe outbreaks damage to the crops in the tropics under global warming.     

Thermal niche overlap of the corner recluse spider Loxosceles laeta (Araneae; Sicariidae) and its possible predator,the spitting spider Scytodes globula (Scytodidae)

Loxoscelism is a health problem caused by the bite of spiders of the genus Loxosceles. In Chile all cases are attributable to Loxosceles laeta. It has been suggested that the spitting spider Scytodes globula may be a predator of L. laeta and control its population, which is only possible if they share the microhabitat. This study compared the thermal preferences and tolerances of the two species. Later, spiders acclimated to 15 °C and 25 °C were exposed to decreasing and increasing temperatures to determine the lower and upper critical temperatures. The preferred temperatures were lower during the morning, but there were no differences between the species. The thermal niche breadths were similar for the species, with a large overlap. Both species showed tolerance to extreme temperatures, but L. laeta showed greater tolerance to low temperatures. Both species showed acclimation of the lower critical temperatures to changes in acclimation temperatures. The similarity of preferred and tolerated temperatures was partly an expected fact, since the species share the same macrohabitat; these spider species are very common in domestic environments of central Chile. However, the results imply that their microhabitat choices are also very similar, indicating a high probability of meeting and predation, which could have important consequences in loxoscelism epidemiology.     

Increased acute thermal tolerance and little change to hematology following acclimation to warm water in juvenile Striped Bass,Morone saxatilis

Striped Bass naturally inhabit a wide range of temperatures, yet little is known about the processes that control their acute and chronic temperature limits. The objective of this study was to determine the effect of temperature acclimation on acute thermal maxima and physiology of juvenile Striped Bass. Juvenile fish were acclimated to 15, 25 or 30 °C for 4 weeks, then split into two sampling groups: post-acclimation and post-critical thermal maximum trials. We found that fish survived in all acclimation temperatures with little change to underlying hematology, and that critical thermal maximum (CT_max) increased with increasing acclimation temperature. At CT_max, fish acclimated to 30 °C had elevated plasma cortisol, lactate and potassium levels. These results suggest that, while 30 °C is likely to be outside their thermal optima, Striped Bass can survive at high temperatures. This ability to cope with warm temperatures may provide an advantage with increasing global temperatures.

     

Temperature selection and avoidance in the sand goby,Pomatoschistus minutus (Pallas), collected at different seasons

Synopsis The sand goby from the Oslofjord, Norway, is extremely eurythermal. In spring and autumn it avoids temperatures lower than about 4° C, in summer 6° C. Acclimation did not influence the lower avoidance temperature, but the critical thermal maximum, the upper avoidance temperature and the temperature where the whole fish darkened (the darkening temperature) varied with acclimation and season. The darkening temperature is suggested to be the upper temperature limit with the greatest ecological significance. The fish, collected at different seasons darkened at between 19.5 and 22° C. In the field the fish is not found at 20° C and higher.The preference temperature varied with season and with acclimation temperature, generally with low precision. In May, the preference temperature was 13.5° C, that is higher than the ambient temperature of 10° C. In summer, the temperature in sampling locality and preference temperature was the same, 17 and 16.5° C respectively. In October, temperature preference was 7.5° C as compared to 9° C in the field. The variation is explained as a behavioural thermoregulation to direct the fish towards optimal conditions at any time.The seasonal variation in preference temperature can not be ascribed only to seasonal variation in temperature, that is an acclimation phenomenon, but other factors are operative as well, factors which will modify the temperature tolerance in the fish.     

Hot or not? Comparative behavioral thermoregulation,critical temperature regimes,and thermal tolerances of the invasive lionfish <Emphasis Type="Italic">Pterois</Emphasis> sp. versus native western North Atlantic reef fishes

Temperature influences the geographic range, physiology, and behavior of many ectothermic species, including the invasive lionfish Pterois sp. Thermal parameters were experimentally determined for wild-caught lionfish at different acclimation temperatures (13, 20, 25 and 32 °C). Preferences and avoidance were evaluated using a videographic shuttlebox system, while critical thermal methodology evaluated tolerance. The lionfish thermal niche was compared experimentally to two co-occurring reef fishes (graysby Cephalopholis cruentata and schoolmaster Lutjanus apodus) also acclimated to 25 °C. The physiologically optimal temperature for lionfish is likely 28.7 ± 1 °C. Lionfish behavioral thermoregulation was generally linked to acclimation history; tolerance and avoidance increased significantly at higher acclimation temperatures, but final preference did not. The tolerance polygon of lionfish shows a strong correlation between thermal limits and acclimation temperature, with the highest CT_max at 39.5 °C and the lowest CT_min at 9.5 °C. The tolerance range of invasive lionfish (24.61 °C) is narrower than those of native graysby (25.25 °C) and schoolmaster (26.87 °C), mostly because of lower thermal maxima in the former. Results show that lionfish display “acquired” thermal tolerance at higher and lower acclimation temperatures, but are no more eurythermal than other tropical fishes. Collectively, these results suggest that while lionfish range expansion in the western Atlantic is likely over the next century from rising winter sea temperatures due to climate change, the magnitude of poleward radiation of this invasive species is limited and will likely be equivalent to native tropical and subtropical fishes with similar thermal minima.     

Effect of preoptic lesions on behavioral thermoregulation of green sunfish,Lepomis cyanellus,and of goldfish,Carassius auratus

Summary Sunfish (Lepomis cyanellus) and goldfish (Carassius auratus) acclimated to 5°, 15° and 25 °C were placed individually in a horizontal temperature gradient from 2° to 30 °C where the fish could swim freely. They spent large proportions of time (70%) at temperatures near their acclimation temperature and avoided the extremes. By behavioral selection, internal body temperature was maintained relatively constant. After bilateral medial and lateral preoptic lesions, fish spent random amounts of time at all temperatures available in the gradient and did not maintain a stable body temperature.Support from grants NSF PCM 76-15861 and HEW PHS GM 7143 is acknowledged.     

Respiratory responses to temperature and hypoxia in the nonindigenous Brown Mussel, Perna perna (Bivalvia: Mytilidae), from the Gulf of Mexico

The respiratory responses to increasing temperature and progressive hypoxia were examined relative to temperature acclimation in the nonindigenous, brown mussel, Perna perna (Mytilidae) from the Gulf of Mexico. When oxygen uptake rate (V?_O2) was recorded at near full air O₂ saturation, rate-temperature curves for Texas specimens of P. perna were sigmoidal, V?_O2 generally increasing with increasing temperature but becoming suppressed as temperatures approached 10 and 30 °C, corresponding closely to this species' incipient thermal limits. At each tested temperature, V?_O2 did not differ among individuals acclimated to 15, 20, or 25 °C. Lack of thermal acclimation was also reflected in acclimatory Q₁₀ values>1.0 (range=1.34-2.14) recorded across acclimation groups at test temperatures equivalent to acclimation temperature. Low acute respiratory Q₁₀ values in all acclimation groups across 15-20 °C indicated a limited capacity for thermal regulation of V?_O2 within this temperature range. The ability of P. perna to regulate O₂ uptake with progressive hypoxia was temperature-dependent, increasing from poor O₂ regulation at 10 °C to good regulation at 30 °C. The O₂ regulatory ability of P. perna and other open-water mytilids in declining O₂ concentrations does not greatly differ from that of estuarine heterodont bivalves, suggesting that it is not a major factor preventing open-water species, such as P. perna, from invading estuarine environments. However, P. perna's inability to regulate O₂ uptake at temperatures>25 °C combined with its relatively low upper thermal limit of 30 °C will likely prevent it from establishing permanent estuarine populations on Gulf of Mexico shores.     

Thermal maxima for juvenile shortnose sturgeon acclimated to different temperatures

Many populations of shortnose sturgeon, Acipenser brevirostrum, in the southeastern United States continue to suffer from poor juvenile recruitment. High summer water temperatures, which may be exacerbated by anthropogenic activities, are thought to affect recruitment by limiting available summer habitat. However, information regarding temperature thresholds of shortnose sturgeon is limited. In this study, the thermal maximum method and a heating rate of 0.1°C min⁻¹ was used to determine critical and lethal thermal maxima for young-of-the-year (YOY) shortnose sturgeon acclimated to temperatures of 19.5 and 24.1°C. Fish used in the experiment were 0.6 to 35.0 g in weight and 64 to 140 days post hatch (dph) in age. Critical thermal maxima were 33.7°C (±0.3) and 35.1°C (±0.2) for fish acclimated to 19.5 and 24.1°C, respectively. Critical thermal maxima significantly increased with an increase in acclimation temperature (p < 0.0001). Lethal thermal maxima were 34.8°C (±0.1) and 36.1°C (±0.1) for fish acclimated to 19.5 and 24.1°C, respectively. Lethal thermal maxima were significantly affected by acclimation temperature, the log₁₀ (fish weight), and the interaction between log₁₀(fish weight) and acclimation temperature (p < 0.0001). Thermal maxima were used to estimate upper limits of safe temperature, thermal preferences, and optimal growth temperatures of YOY shortnose sturgeon. Upper limits of safe temperature were similar to previous temperature tolerance information and indicate that summer temperatures in southeastern rivers may be lethal to YOY shortnose sturgeon if suitable thermal refuge cannot be found.     

Northern grass lizards (<Emphasis Type="Italic">Takydromus septentrionalis</Emphasis>) from different populations do not differ in thermal preference and thermal tolerance when acclimated under identical thermal conditions

We acclimated adults of Takydromus septentrionalis (northern grass lizard) from four localities (populations) under identical thermal conditions to examine whether local thermal conditions have a fixed influence on thermal preference and thermal tolerance in the species. Selected body temperature (Tsel), critical thermal minimum (CTMin), and critical thermal maximum (CTMax) did not differ between sexes and among localities in lizards kept under identical laboratory conditions for ∼5 months, and the interaction effects between sex and locality on these measures were not significant. Lizards acclimated to the three constant temperatures (20, 25, and 35°C) differed in Tsel, CTMin, and CTMax. Tsel, CTMin, and CTMax all shifted upward as acclimation temperature increased, with Tsel shifting from 32.0 to 34.1°C, CTMin from 4.9 to 8.0°C, and CTMax from 42.0 to 44.5°C at the change-over of acclimation temperature from 20 to 35°C. Lizards acclimated to the three constant temperatures also differed in the range of viable body temperatures; the range was widest in the 25°C treatment (38.1°C) and narrowest in the 35°C treatment (36.5°C), with the 20°C treatment in between (37.2°C). The results of this study show that local thermal conditions do not have a fixed influence on thermal preference and thermal tolerance in T. septentrionalis.