Efficacy of oral praziquantel treatment against the skin fluke infection of cultured chub mackerel, Scomber japonicus

Outbreaks of skin flukes and associated mortalities have been observed in cultured chub mackerel, Scomber japonicus. Although freshwater bathing effectively removes the parasites, large post-treatment mortalities are occasionally observed especially under high water temperature conditions due to the stress from handling and confinement. Since outbreaks of the skin fluke infections often occur in high temperature seasons, development of an effective and safe control method is essential for the advancement of mackerel aquaculture. The present study aims to: 1) identify the skin fluke of cultured chub mackerel and 2) develop an alternative control measure using oral drug administration. The skin fluke was identified as Neobenedenia girellae by morphology and molecular data targeting ITS region of rDNA. Two trials of oral administration of praziquantel (PZQ), a common anthelmintic, were conducted and parasite intensity was compared before and after the treatment and between treated and untreated control fish. Fish rejected PZQ-coated commercial pellets, but oral administration was successfully achieved using frozen krill as a basal diet The three-day administration with a dose of 150 mg.kg(-1) BW.day(-1) resulted in over 80% reduction in worm intensity. However, some proportion of the skin flukes survived the drug treatment The resistance to PZQ does not relate to worm's developmental stage. Freshwater bathing was more effective and eradicated the parasite, but some post-treatment mortality of host fish was observed. Moreover, the parasite intensity drastically increased after the freshwater bathing, possibly due to stress and loss of mucus during the bathing. The study indicates the PZQ oral treatment is effective to control N. girellae in chub mackerel aquaculture when the drug is properly administrated with an appropriate feeding technique. (C) 2011 Elsevier B.V. All rights reserved.