Non-infectious gill disorders of marine salmonid fish

Gill disorders present a significant challenge in salmon (Salmo salar and Oncorhynchus sp.) farming regions throughout the world. This review of gill disorders and diseases of marine fish is focused on the non-infectious causes of gill disease in marine stage salmonids and these are grouped into harmful algae, such as Karenia mikimotoi, harmful zooplankton, such as Pelagia noctiluca, other environmental challenges, such as pollutants, as well as nutritional and genetic or congenital causes. The present level of understanding of these gill disorders is reviewed with regard to risk factors, potential impacting factors, methods of best practice to mitigate non-infectious gill disease and disorders, as well as knowledge gaps and avenues for future research.