In vitro and in vivo evaluation of quinine in gilthead sea bream, Sparus aurata naturally infected with the ciliate Cryptocaryon irritans

The use of quinine as a potential antiparasitic compound was evaluated at cellular level and in naturally infected gilthead sea bream, Sparus aurata with the ciliate Cryptocaryon irritans. Quinine concentrations up to 10μg/ml (30μΜ) did not exhibit any in vitro hemolytic or pro-apoptotic effects on red blood cells or head kidney macrophages, respectively. Dietary administration of quinine in gilthead sea bream at a concentration of 100mg/kg fish for 10days was incomplete due to palatability problems after the fifth day post treatment. A decreasing distribution profile of quinine was evident in the analyzed tissues even during the period where quinine consumption was supposedly ensured. The highest concentrations were measured on day 1 reaching 8.98±3.85μg/ml (27μΜ), 1.33±0.45μg/g and 0.75±0.48μg/g in plasma, skin and gills respectively. Quinine was rapidly removed from the tissue compartment while it remained at low concentration in fish circulation after therapy. A 100% C. irritans prevalence was accompanied with no mortalities during the experiment. Parasitic intensity, measured as trophont number, was significantly reduced in quinine-treated fish at the first sampling point (3rd day: 8±0.8 vs 11±2.6), while no statistical differences were observed thereafter. A significant reduction in plasma glucose level was also observed at the same time point. Organoleptic evaluation in fillets, showed no difference in the flesh bitterness between quinine-treated and control fish.