Aerobic Exercise Training With Optimal Intensity Increases Cardiac Thermal Tolerance in Juvenile Rainbow Trout

Abstract

Domestication and selective breeding for rapid-growth have impaired the cardiorespiratory system of salmonids, which might compromise their capacity to tolerate environmental stressors, such as heat waves. Exercise training by swimming has been proposed as a potential tool to enhance growth, cardiac function and disease resilience in farmed fish and thereby improves aquaculture production. However, whether exercise training could also improve cardiac robustness against heat waves, which are becoming more common and cause severe challenges to aquaculture, remains unknown. Here, we trained juvenile rainbow trout at three different training velocities: 0.06 m*s-1 (or 0.9 body lengths per second [bl*s-1]; control group), 0.11 m*s-1 (or 1.7 bl*s-1; medium speed group) and 0.17 m*s-1 (or 2.7 bl*s-1; high speed group) for 5 weeks, 6h per day, 5 days per week. Measuring maximal heart rate (fHmax) during acute warming, we demonstrated that training at 1.7 bl*s-1 was optimal in order to increase the temperature at which fHmax reached its peak (Tpeak) as well as the upper thermal tolerance of the cardiovascular function (arrhythmia temperature, TARR), up to 3.6°C as compared to the control fish. However, more intensive training did not provide similar improvement on thermal tolerance. Both training regimes enhanced the ventricular citrate synthase activity which may provide higher aerobic energy production capacity for ventricles. Further mechanistic studies are needed to understand the complex interactions between training intensities and changes in thermal tolerance. Although not conclusive on that point, our findings present a valid training programme for hatchery salmonids to increase their cardiac thermal tolerance and consequently probably also their capacity to tolerate heat waves, which has a direct application for aquaculture.

Are resistances to acute hyperthermia or hypoxia stress similar and consistent between early and late ages in rainbow trout using isogenic lines?

“…Numerous solutions exist to reduce the adverse effects of heat waves on aquaculture productions including nutrition, genetic selection, engineering and management (Reid et al, 2019). Pettinau et al (2022) also demonstrated that it was possible to increase cardiac hyperthermia resistance of fish with aerobic exercise training. Given the extent of the problem, it is likely that no solution will be enough by itself and that the best option will probably consist in combining different approaches.…”

Tissue-specific metabolic enzyme levels covary with whole-animal metabolic rates and life-history loci via epistatic effects

“…[57]), and temperatures at or above 20°C are often implemented when measuring maximal enzyme activities in Salmonids (e.g. [26,58]). To normalize the metabolic enzymatic activities to the total tissue mass, total protein concentrations were quantified using the Pierce BCA assay (ThermoFisher Scientific).…”

“…The advantages of studying CS and LDH activities as proxies of mitochondrial content (and therefore aerobic capacity) and anaerobic capacity, respectively, are that their maximal activities can be measured in high throughput from frozen tissue samples across tissues with different functional roles. For example, glycolysis fuels fast-twitch (white) muscle anaerobically during burst swimming [22], while cardiac muscle typically has high capacity for both anaerobic and aerobic metabolism to maintain energy supply during routine function [23][24][25][26][27]. Although metabolic enzymes can be produced in excess in relation to performance needs [28], maintaining high mitochondrial content and anaerobic capacity is costly, thus among-individual variation in tissue-specific metabolic activities reflects differences in energy allocation [29].…”

“…The four tissues included in this study (heart, liver, intestine and white muscle) were selected based on their relevance for organismal energy metabolism. The cardiac muscle is central for delivering oxygen to tissues, and its mitochondrial density and anaerobic capacity often reflect cardiac performance [24][25][26], contributing to endurance swimming and coping with stressors (e.g. [48]).…”

Genetic architecture of acute hyperthermia resistance in juvenile rainbow trout (Oncorhynchus mykiss) and genetic correlations with production traits

“…Adaptation strategies must therefore be established to guarantee food security by limiting production losses induced by heat waves. Promising strategies include engineering solutions, species diversification, better farm management, nutrition, exercise training or genetic improvement [8, 9]. Genetic improvement by selective breeding is an interesting solution to enhance fish resistance to acute hyperthermia conditions as genetic gain is cumulative and can be quickly disseminated in farms thanks to the high fecundity of fish.…”