Anti-parasitic effect of lacquer tree Rhus verniciflua Stokes lignum against Miamiensis avidus (Ciliophora: Scuticociliatida)

Abstract

Scuticociliatosis is a disease in marine fishes worldwide, especially in olive flounder (Paralichthys olivaceus), and is caused by the ciliate Miamiensis avidus (syn. Philasterides dicentrarchi). To find an effective preventive measure against M. avidus, the usefulness of lignum extract from Rhus verniciflua Stokes (RVS; lacquer tree) was investigated. The maximum anti-parasitic activity and extraction yield for RVS lignum were optimised using response surface methodology with the three-factor–three-level Box–Behnken design model (BBD). The optimised extract (OE) contained major active compounds of gallic acid, fustin, and fisetin at concentrations of 3.07 ± 0.06%, 19.77 ± 0.42%, and 2.52 ± 0.02%, respectively. An in vitro parasite killing study showed that the minimum lethal concentration of OE was 225 ppm, whereas that of individual compounds was 100 ppm for gallic acid, 500 ppm for fustin, and 1000 ppm for fisetin. The in vivo experimental results showed that fish that were fed OE-incorporated feed at 100 mg/kg body weight/day for 1–2 weeks had significant preventive efficacy against M. avidus without any toxic effect. Thus, the OE of RVS lignum can act as an effective and safe natural therapeutic agent to control M. avidus in cultured olive flounder.