Ballagh, D.A., Pankhurst, P.M. and Fielder, D.S., 2011. Embryonic development of mulloway, Argyrosomus japonicus, and egg surface disinfection using ozone. Aquaculture, 318: 475–478.

Summary

Mulloway are cultured in Australia for wild stock enhancement and for an emerging aquaculture market. Like other aquaculture species, mulloway are susceptible to pathogens such as bacterial contamination, parasites and viruses that can affect the viability of eggs and larvae. Transfer of pathogens from parent broodstock to offspring can be reduced by soaking the eggs in disinfectants including iodine or more commonly, ozone. Ozone gas dissolved in water has been effective in killing viruses and bacteria in a range of hatchery-reared fish species.

The strength of ozone used to disinfect fish eggs is measured using a CT value (the concentration of ozone [mg/l] multiplied by the contact time [min]) and studies have reported successful inactivation of some viruses using an ozone CT value of 0.1 – 0.25. However, ozone can also be harmful to the fish eggs themselves and therefore, tolerance of eggs to ozone must be assessed for each species of fish.

One problem that can occur after fish eggs are treated with ozone is that the eggs fail to hatch due to damage to the egg surface. The optimal ozone treatment was not known for mulloway eggs.

The aim of this study was to determine the optimal stage of egg development and concentration of ozone for development of disinfection protocols for mulloway eggs. Five concentrations of ozone were combined with three water temperatures and mulloway eggs of 4 stages of development ranging from newly spawned to nearly hatching were exposed to the ozone and temperature combinations. The success of egg hatching was evaluated.

Results showed that mulloway eggs should be treated with ozone of 1 mg/l for 1 minute at 22 °C. This was the highest concentration that mulloway eggs could be exposed to without affecting their ability to hatch. Provided the eggs were treated with this combination of ozone and temperature, it didn’t matter what stage of development the eggs were as all eggs hatched successfully.