The copepod parasite Lernantropus kroyeri impairs the productivity of European sea bass (Dicentrarchus labrax) culture by leading to a direct infection or as a vector for other disease agents. In current conditions, the parasitic infections in mariculture are usually treated with the chemicals, mainly with the pesticides. However, therapeutic chemical use has potential risks on the overall aquatic environment. Thus, the aquaculture sector needs to find alternative substances to the treatment or prophylaxis of the diseases instead of chemicals. In the present study, in vitro exposure tests were performed to elucidate the effects of garlic (Allium sativum) and onion (Allium cepa) on adult L. kroyeri. Female individuals of L. kroyeri were exposed to different concentrations of garlic or onion juice (20, 40, 60, 80 and 100% of the plant juice) for a specified time. Garlic juice exposure at a ratio of 100% resulted in instantaneous death of all individuals in five minutes. Although the killing time varied by the concentration, garlic juice killed the L. kroyeri females within 30 min even at the lowest concentration. Onion juice had lower killing effect at low concentrations, however, higher concentrations of onion juice killed the female parasites within 60 min. Results revealed that garlic and onion juices had killing effect on L. kroyeri females in a time and concentration-dependent manner. It can be concluded that against parasitic copepods alternative solutions can be developed in aquaculture, using these plant juices with emphasising necessity of further in vivo tolerance tests in fish. HIGHLIGHTSGarlic and onion juices had anti-parasitic effect in vitro on the crustacean parasite, Lernantropus kroyeri found on the gills of European sea bass (Dicentrarchus labrax). After exposure of L. kroyeri to garlic and onion juices, the mortality was time and concentration-dependent. The killing activity of garlic juice for L. kroyeri was stronger than that of onion juice. ARTICLE HISTORY

The Monogenean parasite, Dactylogyrus sp., is being considered as one of the most dangerous pathogens in freshwater fish with a high infestation in common carp (Cyprinus carpio). The treatment of parasites including Monogeneans is an important part of fish health maintenance in the overall cycle of aquaculture. Novel applications of natural plant products to eradicate the parasites have taken high attention in aquaculture since they are reported to have less adverse impacts on the environment and fish in comparison to other chemical treatments. In the present study, in vitro antiparasitic effects of the ginger (Zingiber officinale) bulb and pomegranate (Punica granatum) peel against Dactylogyrus sp. were investigated by using in vitro tests. Individuals of the parasite were exposed to different concentrations of ginger (10, 50, 100, and 250 mg/ml) and pomegranate peel (50, 100, 250, and 500 mg/ml) for a specified period. In vitro cumulative mortality values reached 100% in 5 minutes after exposure to ginger at the concentration of 250 mg/ml in 9 minutes after exposure to 100 mg/ml and 50 mg/ml. Cumulative mortality was 58% in 9 minutes after exposure to ginger at the concentration of 10 mg/ml. In in vitro pomegranate tests, cumulative mortality values were assessed 100% in 3 minutes after exposure to pomegranate peel at the concentration of 500 mg/ml and in 6 minutes after exposure to 250 mg/ml and 100 mg/ml. Cumulative mortality was 66% in 6 minutes after exposure to pomegranate peel at the concentration of 50 mg/ml. In vitro results revealed that ginger and pomegranate peel solutions had antiparasitic effects on Dactylogyrus sp. to some degree, depending on solution concentration and exposure time. The efficacy of the ginger and pomegranate peel solutions against Monogeneans should be confirmed in fish through in vivo tests.