Antiparasitic effect of matrine and oxymatrine (quinolizidine alkaloids) on the ciliate Cryptocaryon irritans in the red sea bream Pagrus major

The antiparasitic effect of matrine and oxymatrine, the main alkaloidal constituents of the roots of Sophora flavescens, on Cryptocaryon irritans in vitro and in vivo was investigated. Matrine and oxymatrine completely stopped all ciliary movements of C. irritans theronts in vitro. In vivo trials were first conducted with uninfected red sea bream, Pagrus major fed a commercial pellet feed modified to contain matrine or oxymatrine (0.1 or 0.5 g·kg− 1). The doses were determined by HPLC analysis of the water extract of the S. flavescens roots used in our study. After seven days on the experimental test feed, approximately 50,000 hatched theronts were added to each tank, and the fish were maintained on the experimental feed for three additional days. The matrine-treated feed demonstrated potent anti-C. irritans activity, with the number of parasites reduced by 58% in the 0.5 g·kg− 1 of matrine-fed group. The oxymatrine-treated feed also showed weaker anti-C. irritans activity compared to matrine. Therefore, the main anti-C. irritans activity of the water extract of S. flavescens was considered to be due to matrine. In an 80-day oral challenge trial with P. major, the fish in the group treated with matrine (0.5 g·kg− 1 feed) survived throughout the experimental period against the infestations of C. irritans, which contrasts with the 100% mortality seen in the control group. Furthermore, the number of parasites in the group treated with matrine was reduced by 35% as compared to the control group when C. irritans infected fish fed matrine-treated feed (0.5 g·kg− 1) for 3 days. These results suggested that matrine could be a useful therapeutic agent against the infestations of C. irritans.