TOLERANCE OF THE ROTIFER BRACHIONUS-PLICATILIS TO OZONE AND TOTAL OXIDATIVE RESIDUALS

Live prey items, such as the rotifer Brachionus plicatilis, are an ess ential component of many marine larval production systems. However, in intensive larval rearing systems live food items are also a potential source of pathogens which could adversely affect survival of the larv ae. Consequently, it would be advantageous to reduce or eliminate pote ntial pathogens associated with rotifers and their culture water prior to feeding. Ozone is a strong oxidizing agent which can be utilized a s a disinfectant. Ozone is utilized extensively by commercial operator s for disinfection and treatment of culture water, but there is limite d data on tolerance of rotifers to ozone, residual oxidants associated with using ozone in seawater and the efficacy of an ozone wash. This study sought to evaluate the effects of exposing rotifers to ozone and /or residual oxidants associated with the use of ozone in seawater. Un der the described conditions, the rotifer was found to be sensitive to ozonated seawater, both as total residual oxidants (TRO) consisting o f ozone, chloramines and bromamines and residual oxidants (RO) excludi ng ozone. A ''no observable effect concentration'' (NOEC) of 0.22 mg/L TRO was determined for maximum survival of the rotifers. High levels of ozone (greater than or equal to 1.63 mg/L) were found to inactivate rotifer eggs. Based on published values of the inactivation of bacter ial and viral pathogens, a NOEC of 0.22 mg/L TRO would appear to be su fficient to inactivate a variety of surficial potential pathogens. Con sequently, the utilization of an ozone bath is suitable for the surfic ial disinfection of rotifers prior to feeding and hence may help reduc e the vertical transmission of potential pathogens. Although RO did no t appear as toxic as TRO, rotifers were sensitive to RO remaining in s eawater after the dissipation of ozone. A NOEC of 0.3 mg/L for a 1 min exposure or 0.5 mg/L for a 5 or 10 min exposure time was observed for RO. Due to potential adverse effects of RO, it is recommended that RO be neutralized if ozone-treated water is to be used to culture rotife rs.