Neurobiological responses to fishing gear in wild Atlantic cod (Gadus morhua)

There is an increasing interest in the capture and welfare of wild caught fish. Despite this, the methods used to catch and kill fish in commercial fisheries remain associated with significant welfare concerns. It is therefore necessary to determine neurophysiological, and endocrine responses of fish to different fishing gear in order to understand and highlight the welfare challenges affecting wild fish populations. We characterized neuronal activity, neuroendocrine, neurochemical and molecular responses of wild cod caught with Danish seine, fish traps, longline or gillnet. Fish caught by Danish seine had a significant region-specific increase in neuronal activity in the tubercular nuclei (TN) of the hypothalamus, accompanied by a reduced stress response profile in monoamine neurochemistry and plasma cortisol, in comparison to fish caught with the other fishing methods. In contrast, the fish caught with gillnet displayed the highest stress response reactivity. Total transcriptome analysis of the TN revealed that fish caught by gillnet, longline and fish traps had a neural gene expression pattern associated with energy metabolism, neuroinflammation and neurodegeneration. This suggests that the stress imposed by these fishing methods activates pathways that, over time, may lead to neural dysfunction. These results emphasize that Danish seine-caught fish had relatively better welfare compared to fish caught using the other fishing methods, whereas the gillnet-caught fish had relatively poorer welfare outcomes. Furthermore, we present several candidate genes that may be suitable as markers for stress-related neurodegenerative conditions that should be further studied to elucidate their specific functions within the fish brain.