Differences in neurochemical profiles of two gadid species under ocean warming and acidification.

BACKGROUND

Exposure to future ocean acidification scenarios may alter the behaviour of marine teleosts through interference with neuroreceptor functioning. So far, most studies investigated effects of ocean acidification on the behaviour of fish, either isolated or in combination with environmental temperature. However, only few physiological studies on this issue were conducted despite the putative neurophysiological origin of the CO-induced behavioural changes. Here, we present the metabolic consequences of long-term exposure to projected ocean acidification (396-548 μatm CO under control and 915-1272 μatm under treatment conditions) and parallel warming in the brain of two related fish species, polar cod (, exposed to 0 °C, 3 °C, 6 °C and 8 °C) and Atlantic cod (, exposed to 3 °C, 8 °C, 12 °C and 16 °C). It has been shown that is behaviourally vulnerable to future ocean acidification scenarios, while demonstrates behavioural resilience.

RESULTS

We found that temperature alters brain osmolyte, amino acid, choline and neurotransmitter concentrations in both species indicating thermal responses particularly in osmoregulation and membrane structure. In changes in amino acid and osmolyte metabolism at the highest temperature tested were also affected by CO, possibly emphasizing energetic limitations. We did not observe changes in neurotransmitters, energy metabolites, membrane components or osmolytes that might serve as a compensatory mechanism against CO induced behavioural impairments. In contrast to , such temperature limitation was not detected in ; however, at 8 °C, CO induced an increase in the levels of metabolites of the glutamate/GABA-glutamine cycle potentially indicating greater GABAergic activity in . Further, increased availability of energy-rich substrates was detected under these conditions.

CONCLUSIONS

Our results indicate a change of GABAergic metabolism in the nervous system of close to the optimum of the temperature range. Since a former study showed that juvenile might be slightly more behaviourally resilient to CO at this respective temperature, we conclude that the observed change of GABAergic metabolism could be involved in counteracting OA induced behavioural changes. This may serve as a fitness advantage of this respective species compared to in a future warmer, more acidified polar ocean.