Quantification of parasite abundance: A novel method to evaluate anti-Cryptocaryon irritans efficacy

Abstract

Cryptocaryon irritans can cause mass mortality of cultured marine fish. There are few strategies that are efficacious for the control of the agent. As such, a robust assessment of alternative/novel chemotherapeutic agents against parasites within infected hosts is needed. This study aimed to establish a novel method by designing a particular device to determine parasite abundance for evaluating anti-C. irritans efficacy. A device was designed, which is primarily consists of an enclosure and a placemat. The device was used to determine the regular pattern of C. irritans shedding from infected Trachinotus ovatus. A positive correlation was observed between different inoculum doses and parasite abundance. The parasite sampling method was also used to evaluate the effect of amprolium hydrochloride dose (0, 0.5, 1.0, and 2.0 g/kg feed) against C. irritans infection. The results showed that the device collected >99.86% tomonts at 2–4 days of post-infection. Furthermore, a linear model was established to analyze infectious dose and parasite abundance (y = 192.5 + 3.961×). The coefficient of determination (R2) value was 0.990. The results of the amprolium hydrochloride treatment showed that the parasite abundance in the chemotherapeutic treatment groups were significantly reduced by 14.54%, 20.61%, and 37.10%, respectively, compared to the control group. The observed efficacy was dose-dependent, which indicated that the chemical protection against C. irritans infection could be successfully evaluated by this method. Here, a device was designed to accurately measure the number of tomonts, which can be useful in determining parasite abundance and assessing anti-C. irritans efficacy of chemotherapeutics.