Abstract
The effective conditions of glutaraldehyde, chloramine-T, bronopol, Incimaxx Aquatic® and hydrogen peroxide as some biocides commonly used by the aquaculture industry were investigated against F. psychrophilum in sanitization of rainbow trout eyed eggs. Bacteriostatic tests as well as bactericidal tests using ethidium monoazide bromide PCR assays were conducted in vitro on Flavobacterium psychrophilum while impacts of chemical treatments were studied in vivo on 240 [°C × days] rainbow trout eyed eggs. A 20-min contact time with bronopol (up to 2,000 ppm), chloramine-T (up to 1,200 ppm), glutaraldehyde (up to 1,500 ppm), hydrogen peroxide (up to 1,500 ppm) or with Incimaxx Aquatic® (up to 185 ppm, eq. peracetic acid) was effective against F. psychrophilum and did not affect the eyed eggs/fry viability. Collectively, the data obtained here clearly demonstrate that concentrations and duration of treatments commonly used to sanitize eyed eggs are widely overestimated in their effectiveness against F. psychrophilum. The new treatment conditions with the five studied biocides are bactericidal for F. psychrophilum and safe for rainbow trout eyed eggs. In this work, we developed an experimental approach to test some chemicals against fish pathogens to assist fish farmers in the effective and safe disinfection of eyed eggs.
Highlights
Flavobacterium psychrophilum is the aetiological agent of ‘rainbow trout fry syndrome’ (RTFS) and ‘bacterial coldwater disease’ (BCWD), the two most significant systemic infections of primarily freshwaterreared salmonid fish [1] such as coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss) and occasionally other fish species such as ayu (Plecoglossus altivelis) [2]
Considerable economic losses to fish aquaculture producers can occur and the erosion of tissue leading to a commercial downgrade of adult fish
Glutaraldehyde, chloramine-T, bronopol, Incimaxx Aquatic® and hydrogen peroxide were individually assayed to assess the capability of such products to inhibit the growth of five F. psychrophilum strains (Table 1)
Summary
Flavobacterium psychrophilum is the aetiological agent of ‘rainbow trout fry syndrome’ (RTFS) and ‘bacterial coldwater disease’ (BCWD), the two most significant systemic infections of primarily freshwaterreared salmonid fish [1] such as coho salmon (Oncorhynchus kisutch), rainbow trout (Oncorhynchus mykiss) and occasionally other fish species such as ayu (Plecoglossus altivelis) [2]. Considerable economic losses to fish aquaculture producers can occur (up to 90% in rainbow trout farmed in Norway [4]) and the erosion of tissue leading to a commercial downgrade of adult fish (for a review of F. psychrophilum biology, clinical signs and BCWD prevention and treatment, [5]). The control of F. psychrophilum infections is difficult and no effective vaccine is available yet despite numerous studies focused on the capability of some F. psychrophilum proteins to induce protection in fish. Some hatchery managers have expressed concerns about user safety and the impact on the environment of such molecules These pharmaceuticals or their metabolic residues (i) may be found inside the fish flesh, (ii) may lead to the emergence of resistant strain pathogens and/or (iii) may have side effects on aquatic organisms accidentally exposed to them. The aquaculture industry seeks to limit the use of antibiotics and emphasizes a preventive approach based on the implementation of effective hygiene measures
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