Acute Stress and an Electrolyte- Imbalanced Diet, but Not Chronic Hypoxia, Increase Oxidative Stress and Hamper Innate Immune Status in a Rainbow Trout (Oncorhynchus mykiss) Isogenic Line

Abstract

In aquaculture, fish may be exposed to sub-optimal rearing conditions, which generate a stress response if full adaptation is not displayed. However, our current knowledge of several coexisting factors that may give rise to a stress response is limited, in particular when both chronic and acute stressors are involved. This study investigated changes in metabolic parameters, oxidative stress and innate immune markers in a rainbow trout ( Oncorhynchus mykiss ) isogenic line exposed to a combination of dietary (electrolyte-imbalanced diet, DEB 700 mEq Kg -1 ) and environmental (hypoxia, 4.5 mg O 2 L -1 ) challenges and their respective controls (electrolyte-balanced diet, DEB 200 mEq Kg -1 and normoxia, 7.9 or mg O 2 L -1 ) for 49 days. At the end of this period, fish were sampled or subjected to an acute stressor (2 min of handling/confinement) and then sampled. Feeding trout an electrolyte-imbalanced diet produced a reduction in blood pH, as well as increases in cortisol levels, hepato-somatic index (HSI) and total energy content in the liver. The ratio between the lactate dehydrogenase (LDH) and isocitrate dehydrogenase (IDH) activities decreased in the liver of trout fed the DEB 700 diet, but increased in the heart, suggesting a different modulation of metabolic capacity by the dietary challenge. Several markers of oxidative stress in the liver of trout, mainly related to the glutathione antioxidant system, were altered when fed the electrolyte-imbalanced diet. The dietary challenge was also associated with a decrease in the alternative complement pathway activity (ACH 50 ) in plasma, suggesting an impaired innate immune status in that group. Trout subjected to the acute stressor displayed reduced blood pH values, higher plasma cortisol levels as well as increased levels of metabolic markers associated with oxidative stress in the liver. An interaction between diet and acute stressor was detected for oxidative stress markers in the liver of trout, showing that the chronic electrolyte-imbalance impairs the response of rainbow trout to handling/confinement. However, trout reared under chronic hypoxia only displayed changes in parameters related to energy use in both liver and heart. Taken together, these results suggest that trout displays an adaptative response to chronic hypoxia. Conversely, the dietary challenge profoundly affected fish homeostasis, resulting in an impaired physiological response leading to stress, which then placed constraints on a subsequent acute challenge.

Effects of stunning methods on pre rigor changes in rainbow trout (Oncorhynchus mykiss) reared at two different temperatures

“…The glucose levels of the CO group was similar to those found in rainbow trout subjected to an acute stressor (around 7.2 mM as a consequence of 2 min of handling/confinement) (Magnoni et al 2019), while the control group used in the same study had a glucose level equal to 5.3 mM, which was similar to that found for the E group in the present study, corresponding to the limit of the physiological level.…”

Mild Effects of Sunscreen Agents on a Marine Flatfish: Oxidative Stress, Energetic Profiles, Neurotoxicity and Behaviour in Response to Titanium Dioxide Nanoparticles and Oxybenzone

“…Supplementary energy supply is needed when the organisms are facing stressful circumstances, and thus diagnosis relying on both aerobic and anaerobic energetic pathways may contribute information regarding the overall energy request [ 68 ]. In this context, IDH and LDH are suitable biomarkers of the energetic metabolism, as the former participates in the aerobic and the latter in the anaerobic pathways.…”

“…NADP + -dependent IDH is found both in mitochondria and cytoplasm catalysing the oxidative decarboxylation of isocitrate into α-ketoglutarate in the Krebs cycle, generating NADPH from NADP + . It is the major source of NADPH required for several important metabolic pathways, including those involved in the defence mechanisms against oxidative stress [ 68 , 69 ] and fatty acid metabolism [ 70 , 71 ]. LDH, in turn, participates in the glycolytic cycle, where it is responsible for the conversion of lactate into pyruvate, in a reversible reaction at anaerobic conditions, and is also involved in the antioxidant cell defence [ 72 ].…”

Multi-Approach Assessment for Stress Evaluation in Rainbow Trout Females, Oncorhynchus mykiss (Walbaum, 1792) from Three Different Farms during the Summer Season

“…However, rainbow trout production is higher in farms, but official reporting is not conducted properly. Compared to wild rainbow trout, farmed fish are exposed to intensive rearing conditions, which can affect welfare and growth [ 3 ]. Knowledge regarding the physiological changes of fish, as a response to stressors, can improve productivity performances, fish welfare, and product quality [ 3 , 4 ].…”

“…Compared to wild rainbow trout, farmed fish are exposed to intensive rearing conditions, which can affect welfare and growth [ 3 ]. Knowledge regarding the physiological changes of fish, as a response to stressors, can improve productivity performances, fish welfare, and product quality [ 3 , 4 ]. Harvesting-related stimuli, such as netting, loading, and unloading, are usually unavoidable and cause detectable physiological responses in food fish that can be deleterious to product quality and value.…”