Argulus infections in fisheries: status, control, and future prospects

Among species farmed for consumption and trade, parasite epidemics are common due to the intense, often stressful conditions required to maximise production. For aquatic culture, parasite infections are often uncontrollable due to a lack of information and research on both parasites and hosts. Fish lice, ectoparasitic crustaceans, cause severe economic loss to industry each year through physical damage to hosts and subsequent secondary infections. Marine sea lice are notorious in salmon farming and have been the subject of intense research over past decades. Conversely, freshwater lice (Genus Argulus) have been relatively ignored. Here, the problems arising from Argulus spp. infections were investigated with the aim of reducing the economic and health impacts of these parasites. A survey of trout fisheries to ascertain the current state of UK Argulus spp. populations highlighted numerous variables associated with problematic infections and exposed a deficit in effective Argulus spp. control measures. Infection dynamics were then assessed with temperature, host species and infection density all playing a key role in Argulus spp. life histories and generation time. New and novel monitoring and control techniques were evaluated to help tackle infections. Light-baited traps and timed chemical dosage based on circadian rhythms have potential, while egg-laying substrate traps removed millions of Argulus spp. eggs from fisheries to reduce the next generation population size. Finally, a new and invading non-native Argulus species was discovered in UK fisheries and described here morphologically and genetically to facilitate future monitoring of this parasite and improve species identification. Argulus spp. will continue to negatively impact fisheries and aquaculture into the future, however the data and information provided here will help develop integrated management systems to improve fish health worldwid