Surface disinfection of cod Gadus morhua and haddock Melanogrammus aeglefinus eggs with bronopol

Using current practice of immersion, the survival of cod eggs disinfected with 50 mg l− 1 to 500 mg l− 1 bronopol (as Pyceze [50%W/V bronopol], Novartis Animal Vaccines Ltd.) for 45 s, was higher (83-89%) when compared with negative controls (48%). Hatching larvae survived exposure to Pyceze but not to Kickstart (25% peracetic acid/hydrogen peroxide, CIDLines UK), a common disinfectant in United Kingdom marine finfish hatcheries. Bacterial numbers on cod eggs were 30 CFU ml− 1 following contact with 50 mg l− 1 bronopol and zero at 1000 mg l− 1 compared with 14,000 CFU ml− 1 with no disinfection. Although survival to hatch of haddock eggs in 50 mg− 1 bronopol (71.6%) was higher than in non-disinfected eggs (62.4%) this was not significant. Haddock eggs required a concentration of 500 mg l− 1 bronopol to achieve a significant reduction in bacterial numbers, 352 cf. 1546 CFU ml− 1 in seawater controls. Alternative techniques to immersion were assessed to reduce repeated handling and possible damage to eggs. A flow-through system utilising a peristaltic dosing pump was ineffective in achieving the target concentration of Pyceze and contact time, but use of a static immersion technique in an incubation unit, with 30 min daily exposure to 50 mg l− 1 bronopol, gave 63% survival to hatch compared with 35% with a negative control. Bacterial numbers of 892 CFU ml− 1 following treatment with Pyceze were significantly lower than the 91,400 CFU ml− 1 in negative controls. In target animal safety studies with 250 mg l− 1 bronopol, namely × 5 target concentration for 2× exposure time, survival of haddock eggs of 88.7% was significantly higher when compared with 53.1% in non-disinfected.