Anti-Parasitic Effects Of Quinine Sulfate On The Swimming Crab Parasite Mesanophrys Sp.

Mesanophrys sp. is a newly discovered parasitic ciliate, which can cause the death of swimming crabs (Portunus trituberculatus) during the winter period. In this study, the anti-parasitic effects and toxicity of quinine sulfate on Mesanophrys sp. were investigated. In vitro results showed that Mesanophrys sp. mortality rates were 100% when treated with quinine sulfate at 21.0, 18.0, 12.0, 12.0, 12.0, 12.0, and 12.0 mg/L for 0.5, 1, 2, 4, 6, 12, and 24 h, respectively. The 0.5 h-LC50, 1 h-LC50, 2 h-LC50, and 24 h-LC50 of quinine sulfate against Mesanophrys sp. were 11.87, 10.38, 8.71, and 5.23 mg/L, respectively. With the increased concentration of quinine sulfate or the prolongation of the treatment time, the morphology and structure of Mesanophrys sp. changed significantly. The parasites became rounded, cilia were shed, nuclear chromatin agglomerated but then disappeared, the mitochondrial membrane deformed and the ridge structure partially collapsed, cell membranes ruptured and the cytoplasm leaked out. In an in vivo trial, by adding quinine sulfate (12 mg/L) to the culture water, the survival rate of artificially infected crabs was 86.67 +/- 5.77%, which was not significantly different from the survival rate (90%) of the crab in the control group but was significantly higher than the infection group without drug exposure (3.33 +/- 5.77%). The protection rate of the drug against disease was 83.34%. In the treatment test, a dose of quinine sulfate (12 mg/kg) was given three times as an injection into a swimming leg of a crab that had been experimentally infected. Injection resulted in an increase in the survival of infected crabs from 11.11 +/- 9.62% (infection group without treatment) to 77.78 +/- 9.62%. There was no statistical difference in survival between the latter group and the control group (94.44 +/- 9.62%). Finally, the bathing and injection methods caused no apparent harm to the feeding and movement activities of P. trituberculatus.