Abstract
While research into the growth, survival, nutrition and, more recently, disease susceptibility of triploid Atlantic salmon has expanded, there remains an overall lack of studies assessing the response of triploids to chemical treatments. It is essential that the response of triploids to disease treatments be characterised to validate their suitability for commercial production. This study aimed to investigate and compare the stress and immune responses of triploid and diploid Atlantic salmon following an experimental treatment with hydrogen peroxide (H2O2). A dose response test was first undertaken to determine a suitable test dose for both diploid and triploid Atlantic salmon. Following this, diploids and triploids were exposed to H2O2 (1800 ppm) for 20 min, as per commercial practices, after which blood glucose and lactate, and plasma cortisol and lysozyme were measured, along with the expression of oxidative stress and immune-related genes. In the first 6 h post-exposure to H2O2, comparable mortalities occurred in both diploid and triploid Atlantic salmon. Cortisol, glucose and lactate were not significantly influenced by ploidy suggesting that, physiologically, triploid Atlantic salmon are able to cope with the stress associated with H2O2 exposure as well as their diploid counterparts. Exposure to H2O2 significantly elevated the expression of cat and sod2 in diploid livers and gr, il1β and crp/sap1b in diploid gills, while it significantly decreased the expression of saa5 and crp/sap1a in diploid gills. In triploids, the expression levels of cat, hsp70, sod1, saa5, crp/sap1a and crp/sap1b in liver was significantly higher in fish exposed to H2O2 compared to control fish. The expression of gr, sod1 and il1β in triploid gills was also elevated in response to H2O2 exposure. This study represents the first experimental evidence of the effects of H2O2 exposure on triploid Atlantic salmon and continues to support their application into commercial production.
Highlights
As the global population continues to grow, so will the demand for aquaculture food products, with the industry aiming towards the intensification and expansion of production [1,2]
Within the diploid H2O2-exposed fish, significantly lower cortisol levels were observed at 6 h. p.e (190.0 ± 81.7 ng/ml) and 24 h. p.e (178.8 ± 44.4 ng/ml) compared to 1 h. p.e, while levels remained steady in the control fish
This study, representing the first testing of H2O2 in triploid Atlantic salmon, confirmed that exposure to H2O2 triggered primary and secondary stress responses, and that these responses were not significantly influenced by ploidy. This suggests that the physiological response of triploids to cope with the stress induced by H2O2 exposure would be comparable to that observed in their diploid counterparts
Summary
As the global population continues to grow, so will the demand for aquaculture food products, with the industry aiming towards the intensification and expansion of production [1,2]. Disease and resultant health and welfare issues are recognised as one of the largest single causes of economic losses for aquaculture, representing a significant constraint to the industry's continued development and success [5,6,7]. With no vaccine available for the prevention of these parasites, a large proportion of the associated economic losses can be attributed to chemotherapeutic treatments [13]. One such treatment, regularly employed by the aquaculture industry for the control of both sea lice and AGD, is hydrogen peroxide (H2O2) [15,16]
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