In vivo and in vitro assessment of Atlantic salmon skin exposed to hydrogen peroxide

Christian Karlsen,André Sture Bogevik,Aleksei Krasnov,Elisabeth Ytteborg

doi:10.1016/j.aquaculture.2021.736660

Abstract

The salmon louse (Lepeophtheirus salmonis) is a significant problem in Atlantic salmon aquaculture. The industry is forced to use harsh antiparasitic treatments, including hydrogen peroxide (H2O2) baths, to treat the fish. We have utilized in vivo, semi in vivo, and in vitro methods to study the effects of exposures to H2O2. Assessment of external welfare indicators and plasma levels of cortisol, glucose, lactate, and ions did not reveal systemic impacts. Transcriptome analyses showed acute changes in the skin, with transient activation of several transcription factors known as generic stress markers of Atlantic salmon. Post-treatment (24 h), genes involved in the neutralization of free radicals were induced. Expression changes of regulators of cell cycle and cell differentiation were linked to microscopic observations in tissue sections and scale explants cultures. Histology showed adverse effects of H2O2 on skin morphology followed by compensatory recovery, which was not completed after 24 h. Decreased proliferation of cells was observed in keratocyte cultures. Exposure to H2O2, lowered pH (6.8), and elevated temperature (16 °C) markedly decreased the migration of keratocytes, which may indicate a reduced ability to repair skin and compound effects with H2O2. The study adds to the understanding of the adverse effects of hydrogen peroxide and promotes new models in Atlantic salmon skin research.

Highlights

Infections with the ectoparasite salmon lice (Lepeophtheirus salmonis) are among the greatest Atlantic salmon aquaculture problems, affecting production, health, welfare, and the public reputation of the industry (Torrissen et al, 2013; Liu and Bjelland, 2014)
Differences between the time-points were observed within fin and skin status, but there was no significant contribution of H2O2
Skin sections from the in vivo trial sampled at 0 h, 4 h, and 24 h post H2O2 exposure were compared to the control

Summary

Introduction

Infections with the ectoparasite salmon lice (Lepeophtheirus salmonis) are among the greatest Atlantic salmon aquaculture problems, affecting production, health, welfare, and the public reputation of the industry (Torrissen et al, 2013; Liu and Bjelland, 2014). Following a drastic increase in the first part of 2010, the use of H2O2 has reduced in the northern hemisphere due to development of resistance to this treatment in lice (Helgesen et al, 2015). This agent may still be included as a pharmaceutical alternative or reintroduced in comparative treatment regimens (Valenzuela-Munoz et al, 2020). H2O2 removes pre-adult and adult lice by mechanical paralysis induced by bubble development in the hemolymph (Aaen et al, 2014) It affects lice reproduction and viability of their offspring (Valenzuela-Munoz et al, 2020). The secondary responses are associated with the metabolic changes manifested with increased levels of plasma glucose and lactate (Barton, 2002)

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Discussion

Conclusion