Posts Tagged 'fish'

Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species

Mitochondrial respiration is a multi-step pathway that involves matrix and membrane-associated enzymes and plays a key role in acclimation to variable environmental conditions, but until now it has not been clear which of these steps would be most important in acclimation to changing temperatures and CO2 levels. Considering scenarios of ocean warming and acidification we assessed the role and limitation to phenotypic plasticity in the hearts of two Gadoid species adapted to different thermal ranges: the polar cod (Boreogadus saida), an Arctic stenotherm, and the Northeast Arctic population of Atlantic cod (NEAC, Gadus morhua), a cold eurytherm. We analysed the capacity of single enzymes involved in mitochondrial respiration [citrate synthase (CS), succinate dehydrogenase (SDH), cytochrome c oxidase (CCO)], the capacity of the electron transport system and the lipid class composition of the cellular membranes. Juveniles of the two species were held for four months at four temperatures (0, 3, 6, 8 °C for polar cod and 3, 8, 12, 16 °C for NEAC), at both ambient and elevated PCO2 (400 µatm and 1170 µatm, respectively). Polar cod showed no changes in mitochondrial enzyme capacities and in the relative lipid class composition in response to altered temperature or elevated PCO2. The lack of cardiac cellular plasticity together with evidence at the whole-animal level coming from other studies is indicative of little or no ability to overcome stenothermy, in particular during acclimation to 8 °C. In contrast, eurythermal NEAC exhibited modifications of membrane composition towards a more rigid structure and altered enzyme capacities to preserve functionality at higher temperatures. Furthermore, in NEAC, the capacities of SDH, CCO and CS were increased by high levels of CO2 if combined with high temperatures (12 and 16 °C), suggesting the compensation of an inhibitory effect. These results indicate that the cold eurythermal species (NEAC) is able to alter its mitochondrial function to a far greater extent than the Arctic stenotherm (polar cod), indicating greater resilience to variable environmental conditions. This difference in plasticity may underpin differences in the resilience to climate change and affect future species distributions and, eventually, survival.

Continue reading ‘Impact of ocean acidification and warming on mitochondrial enzymes and membrane lipids in two Gadoid species’

Molecular and physiological responses to long-term carbon dioxide exposure in Atlantic salmon (Salmo salar)


• Atlantic salmon was exposed to six CO2 concentrations (5–40 mg/L) for 12 weeks followed by 6-weeks without exposure (<5 mg/L).

• Positive (pH, K+, HCO3− and PCO2) and negative (Na+, Cl−) linear relationships with CO2 exposure were observed as long as CO2 exposure persists, returning to normal levels when CO2 exposure is ended.

• Microarrays analysis of gill tissue detected 71 differentiated expressed genes that responded to CO2 and after termination of exposure 27 down-regulated genes showed compensatory up-regulation.

• The assumption that Atlantic salmon is unaffected by CO2 concentrations below the 15 mg/L threshold should be revised.


Optimal water quality is vital for the growth of Atlantic salmon aquaculture production. Recent data showed that Atlantic salmon feed intake and growth reduce linearly with increasing water carbon dioxide (CO2) concentrations, suggesting that even relatively low concentrations may impact fish performance. This study evaluated the molecular and physiological responses of Atlantic salmon (Salmo salar) to long-term CO2 exposure. For this purpose, Atlantic salmon post-smolts (N = 900; 67 ± 8 g) were exposed to six CO2 treatments (5, 12, 19, 26, 33 and 40 mg/L) for 12-weeks (RAS phase) followed by non-CO2 exposure for a (<5 mg/L) period of 6-weeks (seawaterphase). Results from blood analysis of fish exposed to CO2 for 12 weeks showed that CO2 lead to significantly higher pH, K+, HCO3− and PCO2 and lower Na+ and Cl− plasma concentrations. Whereas, haematocrit, Ca+, Mg2+, urea and glucose concentrations were similar among all CO2 treatments. After 6 weeks in the seawater phase, all the parameters that were previously altered, became similar among all CO2 treatments. Gill microarray results analysis showed 88 differentially expressed genes, resulting from the CO2 exposure. At the end of the RAS phase (week 12), fish exposed to high CO2 (40 mg/L) in comparison to fish exposed to low CO2 (5 mg/L), showed 60 down-regulated genes, including genes encoding proteins involved in immune responses, differentiation, and maintenance of tissue structure. There was no evidence for stress and metabolic changes directed to neutralization of disturbance caused with high CO2. After 6 weeks in the seawater phase, a switch of expression from down regulated to up-regulated was observed. In conclusion, the present study brings new insights on the molecular and physiological responses of Atlantic salmon post-smolts to long-term CO2 exposure. Several osmoregulation and acid-base balance parameters as well as gill gene expression levels were altered for as long as CO2 exposure persisted. Moreover, most of these parameters were linearly related with the environmental CO2 concentrations (5–40 mg/L range). The data from this study adds to recent findings that CO2 concentrations below the 15 mg/L threshold still have an impact on Atlantic salmon. This finding may be relevant for a better dimensioning and management of production systems where CO2 may accumulate in the water such as in recirculating aquaculture systems (RAS).

Continue reading ‘Molecular and physiological responses to long-term carbon dioxide exposure in Atlantic salmon (Salmo salar)’

Energy budget, growth and exercise as proxies for performance capacity and fitness in Arctic fishes

The boreal Atlantic cod (Gadus morhua) is entering the Arctic in response to rising water temperatures, likely increasing predation pressure on the endemic key species Polar cod (Boreogadus saida). In this thesis, I investigated the whole-animal performance of both fish species after long-term acclimation to future ocean acidification and warming conditions in order to estimate their future competitive strength. More precisely, I focused on aerobic performance such as baseline and maximum metabolism, as well as energetic investment into growth and swimming as indicators for fitness capacity under future ocean conditions. While G. morhua was thriving under conditions projected for the year 2100, the competitive strength of B. saida likely decreases. F.i., the growth performance of B. saida decreased at temperatures above 6 degree Celsius and the swimming performance was impaired under elevated PCO2 levels, potentially resulting in a higher vulnerability to predation and reduced foraging success.

Continue reading ‘Energy budget, growth and exercise as proxies for performance capacity and fitness in Arctic fishes’

Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth


• Elevated CO2 and reduced dissolved oxygen have opposite effects on otolith (earstone) development in juvenile copper and blue rockfish.

• Increased CO2 levels resulted in otoliths being larger in area for a relative fish body size in blue rockfish.

• Reduced dissolved oxygen levels results in otoliths being smaller in area for a relative fish body size in both species.


Climate change is predicted to alter ocean chemistry through warming temperatures, increases in CO2 (i.e., ocean acidification), and reductions in dissolved oxygen (DO) (i.e., hypoxia). Past research has shown that early life stages of marine fishes are sensitive to all three stressors, but with sometimes different directions of response. In this study, we examined the separate effects of ocean acidification and hypoxia on otolith growth in two species of juvenile rockfish (copper rockfish, Sebastes caurinus, and blue rockfish, Sebastes mystinus). Fishes were collected at settlement stage from kelp forests on the central California coast and reared in the laboratory for up to 6 months in 4 separate pH treatments (pH = 7.3, 7.6, 7.8, and a control of 8.0), simulating the effects of ocean acidification through the addition of CO2, and 4 separate dissolved oxygen treatments (DO = 2.2, 4.1, 6.0, and a control of 8.7 mg/L), simulating the effects of hypoxia. For both species, otoliths were smaller for a given fish length in response to hypoxia but were larger (trend was non-significant for copper rockfish) in response to elevated CO2. The results suggest that otolith growth may respond differently to ocean acidification and hypoxia for some species, which has implications for sensory development, ecological performance, and interpretations of the permanent record of fish growth in hard parts such as otoliths.

Continue reading ‘Ocean acidification and hypoxia can have opposite effects on rockfish otolith growth’

Rising CO2 enhances hypoxia tolerance in a marine fish

Global environmental change is increasing hypoxia in aquatic ecosystems. During hypoxic events, bacterial respiration causes an increase in carbon dioxide (CO2) while oxygen (O2) declines. This is rarely accounted for when assessing hypoxia tolerances of aquatic organisms. We investigated the impact of environmentally realistic increases in CO2 on responses to hypoxia in European sea bass (Dicentrarchus labrax). We conducted a critical oxygen (O2crit) test, a common measure of hypoxia tolerance, using two treatments in which O2 levels were reduced with constant ambient CO2 levels (~530 µatm), or with reciprocal increases in CO2 (rising to ~2,500 µatm). We also assessed blood acid-base chemistry and haemoglobin-O2 binding affinity of sea bass in hypoxic conditions with ambient (~650 μatm) or raised CO2 (~1770 μatm) levels. Sea bass exhibited greater hypoxia tolerance (~20% reduced O2crit), associated with increased haemoglobin-O2 affinity (~32% fall in P50) of red blood cells, when exposed to reciprocal changes in O2 and CO2. This indicates that rising CO2 which accompanies environmental hypoxia facilitates increased O2 uptake by the blood in low O2 conditions, enhancing hypoxia tolerance. We recommend that when impacts of hypoxia on aquatic organisms are assessed, due consideration is given to associated environmental increases in CO2.

Continue reading ‘Rising CO2 enhances hypoxia tolerance in a marine fish’

Combined effects of ocean acidification and crude oil pollution on tissue damage and lipid metabolism in embryo–larval development of marine medaka (Oryzias melastigma)

Ocean acidification (OA) and crude oil pollution have been highlighted as some of the most pervasive anthropogenic influences on the ocean.In marine teleosts, early life-history stages are particularly vulnerable to disturbance by CO2-driven acidification as they lack pH-mediated intracellular regulation. Embryos exposed to trace levels of crude oil constituents dissolved in water exhibit a common syndrome of developmental abnormalities. So far, little is known about the combined effects of OA and crude oil on the early life history of marine fish. Eggs and larvae of the marine medaka (Oryzias melastigma) were treated with CO2 (1080 μatm atmospheric CO2), the water-soluble fraction (WSF) of crude oil (500 μg/L) and a CO2 (1080 μatm atmospheric CO2)/WSF (500 μg/L) mixture within 4 h after oviposition. Isolated and combined OA/WSF had no detectable effect on embryonic duration, egg survival rate and size at hatching. Histopathological anomalies of tissue and lipid metabolic disorder were significant when CO2 or WSF was given alone at 30 days of age. Combination of CO2 and WSF enhanced their toxicity compared to their separate administration. Since the early life-history stage of marine fish is thought to be impacted more heavily by increasing CO2 partial pressure (pCO2) levels and crude oil pollution, OA and crude oil pollution have the potential to act as an additional source of natural mortality.

Continue reading ‘Combined effects of ocean acidification and crude oil pollution on tissue damage and lipid metabolism in embryo–larval development of marine medaka (Oryzias melastigma)’

Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)


  • Marine fishes will be exposed to multiple stressors under climate change.
  • Hypoxia and high pCO2 are both expected to cause shifts in energy metabolism.
  • No signs of energetic shifts were observed at transcriptomic or enzymatic levels.
  • Multiple stressor transcriptomes are not predictable based on responses to single stressors.
  • Blue rockfish may be relatively tolerant to intensified upwelling conditions.


Global climate change is predicted to increase the co-occurrence of high pCO2 and hypoxia in upwelling zones worldwide. Yet, few studies have examined the effects of these stressors on economically and ecologically important fishes. Here, we investigated short-term responses of juvenile blue rockfish (Sebastes mystinus) to independent and combined high pCO2 and hypoxia at the molecular level, using changes in gene expression and metabolic enzymatic activity to investigate potential shifts in energy metabolism. Fish were experimentally exposed to conditions associated with intensified upwelling under climate change: high pCO2 (1200 μatm, pH~7.6), hypoxia (4.0 mg O2/L), and a combined high pCO2/hypoxia treatment for 12 h, 24 h or two weeks. Muscle transcriptome profiles varied significantly among the three treatments, with limited overlap among genes responsive to both the single and combined stressors. Under elevated pCO2, blue rockfish increased expression of genes encoding proteins involved in the electron transport chain and muscle contraction. Under hypoxia, blue rockfish up-regulated genes involved in oxygen and ion transport and down-regulated transcriptional machinery. Under combined high pCO2 and hypoxia, blue rockfish induced a unique set of ionoregulatory and hypoxia-responsive genes not expressed under the single stressors. Thus, high pCO2 and hypoxia exposure appears to induce a non-additive transcriptomic response that cannot be predicted from single stressor exposures alone, further highlighting the need for multiple stressor studies at the molecular level. Overall, lack of a major shift in cellular energetics indicates that blue rockfish may be relatively resistant to intensified upwelling conditions in the short term.

Continue reading ‘Effects of multiple climate change stressors on gene expression in blue rockfish (Sebastes mystinus)’

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Ocean acidification in the IPCC AR5 WG II

OUP book