Tolerance of the rotifer Brachionus plicatilis to ozone and total oxidative residuals

Abstract

Live prey items, such as the rotifer Brachionus plicatilis, are an essential 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 larvae. Consequently, it would be advantageous to reduce or eliminate potential pathogens associated with rotifers and their culture water prior to feeding. Ozone is a strong oxidizing agent which can be utilized as a disinfectant. Ozone is utilized extensively by commercial operators for disinfection and treatment of culture water, but there is limited 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. Under the described conditions, the rotifer was found to be sensitive to ozonated seawater, both as total residual oxidants (TRO) consisting of ozone, chloramines and bromamines and residual oxidants (RO) excluding 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 (≥ 1.63 mg/L) were found to inactivate rotifer eggs. Based on published values of the inactivation of bacterial and viral pathogens, a NOEC of 0.22 mg/L TRO would appear to be sufficient to inactivate a variety of surficial potential pathogens. Consequently, the utilization of an ozone bath is suitable for the surficial disinfection of rotifers prior to feeding and hence may help reduce the vertical transmission of potential pathogens. Although RO did not appear as toxic as TRO, rotifers were sensitive to RO remaining in seawater 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 rotifers.