In vivo and in vitro treatments against Sparicotyle chrysophrii (Monogenea: Microcotylidae) parasitizing the gills of gilthead sea bream (Sparus aurata L.)

The effect of in vitro and in vivo treatments against Sparicotyle chrysophrii, a microcotylid parasite of gilthead sea bream (Sparus aurata L.), was studied. In vitro chemical treatments were targeted to eggs, oncomiracidia and adults, and were tested both as disinfectants and therapeutics for infected animals. The compounds were: distilled water, formalin, limoseptic ®, hydrogen peroxide, chlorine, and praziquantel (PZQ). Larvae were sensitive to all the treatments, but adults were more resistant, as chlorine (60 ppm - 1 h), hydrogen peroxide (100 ppm - 30 min) and PZQ (50 ppm - 30 min) produced only 10% mortality. All adults were killed only with distilled water, limoseptic (0.1% - 5 min), formalin (300 ppm - 30 min), or hydrogen peroxide (200 ppm - 30 min). Eggs were the most resistant stage, as only 30 min in limoseptic (0.1% in distilled water) or in formalin (300 ppm) prevented hatching. PZQ was used in vivo either as a curative or preventive treatment. The highest dose tested (400 mg kg^− 1 BW; effective dose 116.3 mg kg^− 1 BW due to palatability problems leading to 45% reduction in host food intake) did not significantly decrease prevalence of infection when given for 6 consecutive days. A lower dose (200 mg kg^− 1 BW) (effective dose 158.1 mg kg^− 1 BW) was rejected to a lower degree and decreased the prevalence of infection from 90% to 40%. When a lower dose (40 mg kg^− 1 BW) was administered for longer periods (20 days), food intake was reduced slightly, but the infection did not decrease significantly. The oral intubation with PZQ (200 mg kg^− 1 BW) once a week for 4 weeks did not prevent the infection of fish by cohabitation. However, a significant reduction in the abundance of the parasite was registered. In view of the results, recommendations for fish treatment and disinfection of aquaculture facilities are discussed.