Dispersal of the skin fluke Benedenia seriolae (Monogenea: Capsalidae) by tidal currents and implications for sea-cage farming of Seriola spp.

Sea-cage aquaculture of Seriola lalandi (kingfish) is an emerging industry in Australia with production estimated at 2000 tonnes for 2004/2005. Infections with the monogenean Benedenia seriolae are a major barrier to efficient production and industry growth. Strategic positioning of farms and cages has been identified as a possible husbandry technique to limit parasite population growth, however little information is available on the infection dynamics of this parasite. This study investigated the effect of tidal currents on the dispersal of B. seriolae eggs and on the infection rates of B. seriolae on sentinel fish positioned near a kingfish farm. Two experiments were conducted over intra- and inter-farm scales. In the intra-farm scale experiment, egg density and infection rates at 0, 250, 500 and 1000 m across and inline with tidal current direction from a source were determined by the use of plankton tows (for egg density) and sentinel fish (for infection rates). The density of B. seriolae eggs in the plankton and infection rates on sentinel fish was lower at sites across rather than inline with current direction (no eggs were recovered at sites across tidal current). In the inter-farm scale experiment, the effect of fish farms on infection rates in surrounding waters was determined using sentinel fish placed up to 18 km from the nearest source farm. Results suggest that within the hydrographic conditions studied, dispersal of B. seriolae is considerable and distances greater than 8 km may be required for effective parasite management using independent management units.