In vitro screening and in vivo evaluation of antiparasitic phytochemicals against Cryptocaryon irritans in pompano, Trachinotus ovatus

Abstract

AbstractCryptocaryon irritans, one of the most devastating holotrichous ciliated protozoans, causes massive economic losses in the pompano, Trachinotus ovatus, mariculture industries. Considering the many advantages of phytochemicals, such as low cost, low residuals, and low pollution, they can be a good alternative for the prevention and control of C. irritans infestations. In this study, 14 phytochemicals were evaluated for their antiparasitic activity against the theront of C. irritans, and nine showed significant antiparasitic activity. Nerolidol was the most promising compound, causing 100% mortality of theronts with 30‐min exposure at a concentration of 10.0 μl/L. The half‐maximal inhibitory concentrations (IC50s) of nerolidol on C. irritans theronts, protomonts, and tomonts were 2.1, 13.3, and 7.1 μl/L, respectively. Abnormal morphologies of the theronts, trophonts, and tomonts were observed after exposure to 10.0, 30.0, and 10.0 μl/L nerolidol solution for 15 min, 30 min, and 480 min, respectively. A diet supplemented with 2.3 ml/kg of nerolidol reduced the number of trophonts on the gills of pompano by 95.7% decrease compared with the control groups and the theront chemotaxis to pompano mucus and sera, while increased the survival rate of infected pompanos by 24.44%, and had no significant effect on pompano hindgut and serum myeloperoxidase. These results suggest that nerolidol is a new potential drug for controlling fish cryptocaryonosis.