Parasite attractants: Identifying trap baits for parasite management in aquaculture

Abstract Aquatic parasites may respond to various attractants and cues to find and infect a host. Traps that use these attractants as ‘bait’ have potential to reduce the number of pathogenic agents in aquaculture environments. This study examined four potential attractants (i.e., urea, host mucus, parasite conspecifics and light) and the response of two problematic marine parasite species, to identify the most suitable bait for trap development in finfish aquaculture. Two globally distributed parasite species (i.e., Neobenedenia girellae, Hargis, 1995; and Cryptocaryon irritans, Brown, 1955) were chosen as models. A chemotaxis experiment was used to compare the attractiveness of each species' infectious life stage to urea, host mucus, parasite conspecifics and a seawater control, while a phototaxis experiment was used to identify phototactic responses of the parasites to light or dark. We found that urea and light attracted more than twice the number of infective protozoans and flukes (monogeneans), respectively, compared to other attractants/controls. Cryptocaryon irritans theronts were positively chemotactic to urea (Beta Regression Analysis; Odds Ratio (OR) 2.69, p = 0.00017), while Neobendenia girellae was positively phototactic to light (Mixed Effect Logistic Regression; OR 2.5, p = 0.0014). A final experiment examined the emergence of C. irritans over a 24-hour period and identified that the vast majority excysted at night (ANOVA; p-value