Assessing the effects of stress on the neuroendocrine response of Atlantic cod (Gadus morhua) during the spawning season

Commercial fishing has a significant impact on the welfare of wild fish in terms of stress, yet this topic remains relatively underexplored. This study was conducted with the hope of deepening knowledge on the topic. The thesis investigated the effects of fishing pressure on two different populations of Atlantic cod (Gadus morhua) in Iceland and the Faroe Islands, respectively, caught with longlines and demersal trawlers, both during closed and open seasons to commercial fishing. The aim was to investigate the effects that chronic stress caused by fishing has on the allostatic response, with the focus on the serotonergic (serotonergic, 5-hydroxyindoleacetic acid) and dopaminergic (dopamine and 3,4-dihydroxyphenylacetic acid) systems in three different brain areas associated with stress-coping mechanisms (brain stem, hypothalamus, and telencephalon), as well as on cortisol level in the plasma and gametes. High-performance liquid chromatography (HPLC) was conducted to assess the concentration of the neurotransmitters in each brain part for each sample, while the cortisol content was measured with an ELISA analysis. The samples from the Faroe Islands did not show any significant differences between the open (stress) and closed (non stress) fishing area in terms of monoamines concentration, nor in serotonergic, with the only exception of 5-hydroxyindoleacetic acid in the hypothalamus and the telencephalon as an effect of sex and locations, respectively, nor in the dopaminergic system, except for DOPAC in the brain stem, DOPAC/DA in the hypothalamus proven to be influenced by an interaction of location and sex, and DA in the telencephalon, as an effect of location. The cortisol plasma level, too, did not show any effect, nor for location nor sex. On the contrary, the level of cortisol in the gametes was proven to be linked to sex, with males presenting higher values overall. The confrontation between neurotransmitter content in the Faroe Islands and Icelandic samples proved a significant influence of the fishing method, even if the result might be influenced by errors in the sampling procedures.