Abstract
Several biocides are widely used in rainbow trout aquaculture against various ectoparasites and ectobionts, but the inflammation induced in treated fish is less well described. Dose-response studies were conducted to elucidate the effects on rainbow trout (gills and fins) induced by a series of biocides including formalin, hydrogen peroxide (H2O2), peracetic acid (PAA) and the surfactant SPH6, which was isolated from the bacterium Pseudomonas H6. The compounds have documented antiparasitic effects, but the specific effects on fish needs further documentation. This study was performed over 24 h, and inflammatory reactions were evaluated in gills and fins. A dose-dependent effect was noted for expression of immune genes encoding for IL-1β, TNFα, IFNγ, IL-10, IL-8, lysozyme, serum amyloid A (SAA), hepcidin, precerebellin and complement factor C3. PAA induced the strongest upregulation of cytokine and acute phase reactant genes followed by H2O2 and formalin. SPH6 showed a lower effect, and in several cases the compound induced downregulation of several genes. Gills showed a stronger response compared to fins. The mucous cell density in fins showed a range of changes which varied by compound. PAA, and to a lesser degree H2O2 and formalin, initially induced mucous cell hyperplasia, whereas SPH6 immediately decreased the number of cells containing mucus.
Highlights
Aquaculture production worldwide is challenged by a range of viral, bacterial and parasitic diseases (Woo et al 2020), as systemic infections caused by microorganisms can elicit significant morbidity and mortality (Assefa & Abunna 2018)
The present study examined the effects of SPH6, peracetic acid (PAA), H2O2 and formalin on the expression of these innate immune genes in rainbow trout gills and skin and the mucous cell density in fins over a 24 h exposure period
We documented that especially PAA, and to a lesser extent H2O2 and formalin, induced an increase in superficial mucous cells in the fin, but extended stimulation resulted in an elevated release of mucus
Summary
Aquaculture production worldwide is challenged by a range of viral, bacterial and parasitic diseases (Woo et al 2020), as systemic infections caused by microorganisms can elicit significant morbidity and mortality (Assefa & Abunna 2018). The search for novel and less environmentally detrimental compounds has recently revealed that a novel lipopeptide biocide, isolated from a bacteria Pseudomonas H6 strain (SPH6), is effective against both I. multifiliis (Al-Jubury et al 2018), amoebae (Jensen et al 2020) and the oomycete Saprolegnia (Liu et al 2015). This biologically derived compound may be applied as a control agent in farm settings, but before implementing large-scale usage, any effect on fish health, survival and fish welfare must be fully documented. The present study examined the effects of SPH6, PAA, H2O2 and formalin on the expression of these innate immune genes in rainbow trout gills and skin and the mucous cell density in fins over a 24 h exposure period
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