Chair: Cliff Law

Matthias Schmidt ⁽¹⁾, Hans-Otto Pörtner ⁽¹⁾, Daniela Storch^(1), Christian Bock ⁽¹⁾

¹ Alfred Wegener Institute for Polar and Marine Research, Am Handelshafen 12, 27570 Bremerhaven, Germany

Background
Ocean acidification (OA) as projected for the end of this century has been reported to negatively affect the behaviour of marine fish species. It is suggested that these changes are initiated by a disturbed “ɣ-Aminobutyric Acid A Receptor” as a consequence of increased CO₂ partial pressures (pCO₂) and acid-base regulation. Such disturbance might modulate neurotransmitter levels. We therefore analysed whether OA-induced behaviour reflects changes in specific neurotransmitters in the fish brain depending on environmental temperature. We tested two fish species, Polar cod (Boreogadus saida) whose behaviour is altered by future OWA conditions and Atlantic cod (Gadus morhua) whose behaviour seems to be resilient.

Methods
Polar cod and Atlantic cod were incubated for 3-4 months under 2 different CO₂ concentrations (present day and projected for 2100) and at 4 temperatures specific for their temperature window (0, 3, 6, 8°C for B. saida and 3, 8, 12, 16°C for G. morhua, respectively). Brains from all individuals were directly taken after incubation and shock frozen for further analysis. Non-targeted metabolic profiling using ¹H-NMR spectroscopy was performed on brain extracts for monitoring neurotransmitter and metabolite profiles.

Findings
Concentrations of amino-acid neurotransmitters in both species decreased with increasing temperatures which may have accounted for a reduction of diffusion time in the synaptic cleft with rising temperature. Temperature induced alterations of osmolytes may support enzyme performance. However, in both species, environmental pCO₂ had only a small effect on neurotransmitters and osmolytes.

Conclusions
While this study gives insight into temperature acclimation processes in the brain of fish, we did not detect alterations that might explain why the behaviour of some fish species is resistant to future OA. Species-specific differential use of inhibitory neurotransmitter systems or altered receptor subtype compositions in response to CO₂-pertubation could be the focus of future research.