Antiparasitic effect of dietary Romet®30 (SDMX–OMP) against ciliate Cryptocaryon irritans infection in the red sea bream Pagrus major and tiger puffer Takifugu rubripes

We investigated the effects of dietary Romet®30 (sulfadimethoxine–ormetoprim (SDMX–OMP)) on Cryptocaryon irritans infection in red sea bream Pagrus major and tiger puffer Takifugu rubripes. In Experiment I, 100% mortality of P. major due to C. irritans infection was observed at 10 days and 21 days after exposure to theronts (infective stage) in the a control group without Romet®30 and the group treated with 50 mg Romet®30/kg body weight (BW)/day for 14 days, respectively. Thus, mortality in the treated group was markedly delayed compared with that in the control group. In Experiment II, 100% mortality of P. major in the control group due to C. irritans infection was recorded at 11 days after exposure to theronts. In contrast, mortality due to parasite infection was not observed in the group treated with Romet®30 at 50 mg/kg BW/day for 14 days, and no parasites were found in any surviving fish after 33 days exposure. In addition, the number of parasites on the gills of T. rubripes treated with 50 mg Romet®30/kg BW/day for 14 days was significantly lower than that in the control group after 16 days exposure. These results show that in-feed Romet®30 at 50 mg/kg BW/day for 14 days had antiparasitic and therapeutic effects against C. irritans in both P. major and T. rubripes. Thus, dietary Romet®30 could be useful for controlling C. irritans infection.

► Romet®30 is Sulfadimethoxine–Ormetoprim (SDMX–OMP) combination.
► In-feed Romet®30 had a therapeutic effect against C. irritans infection.
► The suitable dose of Romet®30 was 50 mg/kg BW/day.
► The suitable duration of administration was 14 consecutive days.
► This dosing condition of Romet®30 was practically useful for aquaculture.