Masahiko Katayose

Disinfection of seawater for hatchery aquaculture systems using electrolytic water treatment

A recently marketed electrolytic water treatment system (Hoshizaki) was evaluated for disinfection of seawater used in disease-prone high-intensity aquaculture systems. Bacterial plate counts (CFU), direct bacterial total counts using 4V,6V diamidino-2-phenylindole (DAPI) staining, and viable bacterial total counts using 6-carboxy fluorescein diacetate (6CFDA) showed complete inactivation of bacterial populations at an intensity of z1.3 amp (z2.13 mg Cl l 1 ). This included disinfection of seawater experimentally dosed with the known scallop pathogen Vibrio anguillarum. Experimental use of electrolysis between 1.0 and 4.0 A was able to disinfect cultures of the (food) microalga Isochrysis galbana without deleterious effects on its growth rate. When this technique was applied on a commercial scale in a scallop hatchery, higher microalgal growth rates were achieved compared to those of traditionally autoclaved seawater, or seawater treated with germicidal ultraviolet light (UV). Results suggested that disinfection of hatchery culture waters could be achieved using electrolytic release of very low levels of active Cl ion, providing an effective and economically attractive alternative to currently used methods in these culture systems. D 2002 Elsevier Science B.V. All rights reserved.