Fish skin: far more than a body wrapper
Crucial importance of organ highlighted by speakers at vet conference
The importance of a fish’s skin to its health was hightlighted at the Fish Veterinary Society’s annual conference held at the Norton House Hotel near Edinburgh this week.
“Skin health has emerged as a shared challenge across aquaculture, ornamental and laboratory fish medicine. It sits at the interface between animal welfare, environment, management and diagnostics and increasingly reflects complex multifactorial pressures rather than single tiny entity,” said FVS president Johanna Baily in her introductory address.
Baily, a senior advisor in histopathology at fish health diagnostics company PatoGen, added: “What makes the Fish Vets Society and this meeting special is not just the scientific content but the culture of open and constructive exchange.
“This is a place or a space where experience from the field can be shared honestly, where uncertainty is allowed, and where ideas can be tested without judgment.”
A living, dynamic structure
Dave Cockerill, a vet and director of biochemistry analysis provider WellFish Tech, cited the publication “The robust fish and the protection of 0.07mm”, published by Norwegian company Quantidoc AS, as the source for some of the knowledge he passed on in a presentation during a session on wound healing.
“The skin is more than a body wrapper. We shouldn’t think of it as a jumper that holds everything in,” said Cockerill.
“For terrestrial animals, the surface of the skin is made up of dead keratinised cells which are there to contain moisture and provide a barrier against the hostile dry environment that we now find outselves in, millions of years since we emerged from the swamp.
Aquatic skin is a dynamic living structure actively involved in exclusion and excretion, fluid and electrolyte balance ... we should think of the skin, gut, and gill as a continuous system
“[Terrestrial animal skin] is tough, slow to heal from cuts, and has pathogen-specific immune responses, whereas the aquatic skin is more of a semi-fluid system of mucosal cells, collagen, mucus, which is a much more dynamic living structure actively involved in exclusion and excretion, fluid and electrolyte balance, very sensitive to contact but with incredible healing power in the right circumstances, and is much stronger on the innate immune response.
“We should think of the skin, gut, and gill as a continuous system; there are specialisms for differents parts of the structure but the basic structure is the same.”
Measure earlier
Causes of skin damage include infectious diseases (both specific and opportunistic pathogens) and parasites, nutritional, environmental, sanitary, and technological stressors, and oxidative stress that increases disproportionately with growth rate.
Oxidative stress can have a profound effect on collagen formation and tissue repair, said Cockerill, who argued that fish skin status can and should be measured before end-stage outcomes (mortality or visible lesions) by using biochemistry techniques.
“Characterising and quantifying what’s going on allows us to try different strategies and the evaluate whether those strategies are imporving the outcomes for the fish in supporting skin robustness. We can influence the robustness of the skin and we can actively take management decisions to do so.”
Other speakers included Jamie Smart, of fish health company STIM, who gave a keynote address on topical skin conditions in Scottish aquaculture, and Lene Sveen, of Norwegian research institute Nofima, who has focused her research on fish skin for 10 years.
Sveen, who appeared via a video link from Norway, said the subject of fish skin was too broad to cover in a 15-minute presentation, so she had chosen two of her favourite features of the skin: epithelial cells, which “vacuum clean” the surface of the fish, and the tesselated lymphoid system, T-cells that patrol the skin.
The scientist, whose doctoral dissertation examined injuries to salmon caused by mechanical delousing, said all skin wounds heal the same way, whether the cause was mechanical or bacterial, but infection must be cleared first.
Vaccination works against Moritella viscosa, the cause of winter ulcers, said Sveen, and a recombinant vaccine has been developed to prevent Tenacibaculosis and is now being trialled in Norway.
Research is also taking place on the impacts of gene editing salmon to make them resistant to sea lice, with 16 different types of deletions being tested.
