Thermal acclimation of rainbow trout myotomal muscle, can trout acclimate to a warming environment?

Thermal acclimation in brook trout myotomal muscle varies with fiber type and age

As climate change alters the thermal environment of the planet, interest has grown in how animals may mitigate the impact of a changing environment on physiological function. Thermal acclimation to a warm environment may, for instance, blunt the impact of a warming environment on metabolism by allowing a fish to shift to slower isoforms of functionally significant proteins such as myosin heavy chain. The thermal acclimation of brook trout (Salvelinus fontinalis) was examined by comparing swimming performance, myotomal muscle contraction kinetics and muscle histology in groups of fish acclimated to 4, 10 and 20 °C. Brook trout show a significant acclimation response in their maximum aerobic swimming performance (U_crit), with acclimation to warm water leading to lower U_crit values. Maximum muscle shortening velocity (V_max) decreased significantly with warm acclimation for both red or slow-twitch and white or fast-twitch muscle. Immunohistochemical analysis of myotomal muscle suggests changes in myosin expression underly the thermal acclimation of swimming performance and contraction kinetics. Physiological and histological data suggest a robust acclimation response to a warming environment, one that would reduce the added metabolic costs incurred by an ectotherm when environmental temperature rises for sustained periods of time.

EcoPhysioMechanics: Integrating energetics and biomechanics to understand fish locomotion under climate change

Ecological physiologists and biomechanists have been broadly investigating swimming performance in a diversity of fishes, however the connection between form, function and energetics of locomotion has been rarely evaluated in the same system and under climate change scenarios. In this perspective I argue that working within the framework of 'EcoPhysioMechanics', i.e., integrating energetics and biomechanics tools, to measure locomotor performance and behavior under different abiotic factors, improves our understanding of the mechanisms, limits and costs of movement. To demonstrate how ecophysiomechanics can be applied to locomotor studies, I outline how linking biomechanics and physiology allows us to understand how fishes may modulate their movement to achieve high speeds or reduce the costs of locomotion. I also discuss how the framework is necessary to quantify swimming capacity under climate change scenarios. Finally, I discuss current dearth of integrative studies and gaps in empirical datasets that are necessary to understand fish swimming under changing environments.

Responses of Asian clams (Corbicula fluminea) to low concentration cadmium stress: Whether the depuration phase restores physiological characteristics

The effect of low concentration Cd stress on bivalves is unclear. In this study, Asian clams (Corbicula fluminea) were continuously exposed to 0, 0.05, 0.10, and 0.20 mg/L Cd for 14 d (exposure phase) and to artificial freshwater for 7 d (depuration phase). A total of 16 variables were measured to explore the toxic effects on C. fluminea. All physiological characteristics were significantly inhibited in the treatments (p < 0.05), and the negative effects of Cd did not return to normal levels in the short term. Tissue damage was found in the feet and gills of C. fluminea in all the treatments. On the 7th day (D7), enzyme activity in all the treatments was significantly higher (p < 0.05) than in the control group. Acetylcholinesterase, superoxide dismutase, and catalase activities were enhanced on D14 in all the treatments. However, only glutathione S-transferase activity was significantly higher in all the treatments (p < 0.05) than in the control group on D21. The instability of the enzymes indicated that the adaptability of C. fluminea became stronger throughout the experiment. In each group, the maximum bioaccumulation of Cd followed the order: 0.20 mg/L > 0.05 mg/L > 0.10 mg/L, which might be caused by the filtration capacity of C. fluminea in the 0.05-mg/L group, which was higher than that of the 0.10-mg/L group. Thus, low Cd concentrations effect the physiological characteristics, tissue health, and antioxidant system of C. fluminea and may require a long recovery time to be restored to normal levels.

Temperature effects on the contractile performance and efficiency of oxidative muscle from a eurythermal versus a stenothermal salmonid

We compared the thermal sensitivity of oxidative muscle function between the eurythermal Atlantic salmon (Salmo salar) and the more stenothermal Arctic char (Salvelinus alpinus; which prefers cooler waters). Power output was measured in red skeletal muscle strips and myocardial trabeculae, and efficiency (net work/energy consumed) was measured for trabeculae, from cold (6°C) and warm (15°C) acclimated fish at temperatures from 2 to 26°C. The mass-specific net power produced by char red muscle was greater than in salmon, by 2-to 5-fold depending on test temperature. Net power first increased, then decreased, when the red muscle of 6°C-acclimated char was exposed to increasing temperature. Acclimation to 15°C significantly impaired mass-specific power in char (by ∼40-50%) from 2 to 15°C, but lessened its relative decrease between 15 and 26°C. In contrast, maximal net power increased, and then plateaued, with increasing temperature in salmon from both acclimation groups. Increasing test temperature resulted in a ∼3- to 5-fold increase in maximal net power produced by ventricular trabeculae in all groups, and this effect was not influenced by acclimation temperature. Nonetheless, lengthening power was higher in trabeculae from warm-acclimated char, and char trabeculae could not contract as fast as those from salmon. Finally, the efficiency of myocardial net work was approximately 2-fold greater in 15°C-acclimated salmon than char (∼15 versus 7%), and highest at 20°C in salmon. This study provides several mechanistic explanations as to their inter-specific difference in upper thermal tolerance, and potentially why southern char populations are being negatively impacted by climate change.

An acute increase in water temperature can decrease the swimming performance and energy utilization efficiency in rainbow trout (Oncorhynchus mykiss)

In order to evaluate the effects of acute temperature exposure on the swimming performance of rainbow trout (Oncorhynchus mykiss), the critical swimming speed (U_crit) and oxygen consumption rates (MO₂) were determined at different temperatures (13.2, 18.4, and 22.5 °C). The U_crit and MO₂ of different body mass (109.44, 175.74, and 249.42 g) fish were also obtained at 13.4 °C. The U_crit first increased as the temperature increased from 13.2 to 15.2 °C, which was calculated to be the optimal temperature for the U_crit, and then decreased with increasing temperature. The optimal swimming speed (U_opt) showed a similar trend to the U_crit. At a given swimming speed, the MO₂ and cost of transport (COT) were significantly higher at 22.5 than at 13.2 °C, suggesting the energy utilization efficiency decreased with increasing temperature. The absolute values of U_crit and U_opt increased as the body mass increased from 109.44 to 249.42 g, whereas the relative values decreased. Although not statistically significant, the maximum metabolic rate (MMR) tended to increase with temperature but decrease with body mass. Results can be of value in understanding the behavioral and physiological response of rainbow trout to acute temperature change.

Climate change and anadromous fish: How does thermal acclimation affect the mechanics of the myotomal muscle of the Atlantic salmon, Salmo salar?

In response to accelerated temperature shifts due to climate change, the survival of many species will require forms of thermal acclimation to their changing environment. We were interested in how climate change will impact a commercially and recreationally important species of fish, Atlantic salmon (Salmo salar). As climate change alters the thermal environment of their natal streams, we asked how their muscle function will be altered by extended exposure to both warm and cold temperatures. We performed a thermal acclimation study of S. salar muscle mechanics of both fast-twitch, or white, and slow-twitch, or red, myotomal muscle bundles to investigate how temperature acclimated Atlantic salmon would respond across a range of different temperatures. Isometric contraction properties, maximum shortening velocity, and oscillatory power output were measured and compared amongst three groups of salmon-warm acclimated (20°C), cold-acclimated (2°C), and those at their rearing temperature (12°C). The Atlantic salmon showed limited thermal acclimation in their contraction kinetics, and some of the shifts in contractile properties that were observed would not be predicted to mitigate the impact of a warming environment. For instance, the maximum shortening velocity at a common test temperature was higher in the warm acclimated group and lower in the cold-acclimated group. In addition, critical swimming speed did not vary with temperature of acclimation when tested at a common temperature (12°C). Our results suggest that Atlantic salmon populations will continue to struggle in response to a warming environment.