Toxicity and antiparasitic efficacy of Mebendazole in juveniles of Mugil liza mullet
Mugilidae have a wide distribution around the world and are important in artisanal fishing and in fish farming projects, due to, among others, their high adaptability to growing conditions. Aquaculture is an expanding economy and its success is supported by several factors, including the health of fish and the farming environment. The intensification of the crops added to the other stressful situations, result in fish immunosuppression, increasing the vulnerability to pathologies. In this scenario, interest in the use of chemotherapy is growing more and more to minimize losses caused by parasites and other pathologies. Mebendazole (MBZ) is an anthelmintic commonly used in human and veterinary medicine and has been used successfully in fish. This work sought to establish safe doses,describe the histological damage after therapeutic baths and oral administration with MBZ, determine the antiparasitic efficacy of MBZ used in the form of baths and oral administration to mullets, Mugil liza. To test the safe doses of MBZ, used in 24-hour therapeutic baths, concentrations of zero, 1, 10, 100, 200mg/L and 1 and 5g/L were tested. Fish treated with 10mg/L or more showed some damage to the branchial structure, such as hyperplasia, focal necrosis, telangiectasis, squamous metaplasia and increased mitotic activity. MBZ has already been identified as causing oxidative stress, this suggests that the necrosis was caused by oxidative damage or even by the direct action of MBZ. Hyperplasia was probably caused by an immune response and telangiectasia is related to physical or chemical damage. It was observed that baths,whose MBZ concentrations were equal to or greater than 10mg/L, caused branchial damage that compromised the fish's vital functions. The effectiveness of therapeutic baths with lower concentrations was then tested: 1, 2, 3 and 5mg/L, also with 24 hours. Necropsies were performed before and after all experiments and three groups of parasites were found: Ligophorus sp. (Ancyrocephalidae), Solostamenides sp. (Microcotylidae), both Monogenoidea and Digenea. Concentrations 3 and 5mg/L showed efficacy of 56.9 and 65.8%, respectively, against Ligophorus sp. (p <0.05). The other concentrations were not significantly effective for the other groups of parasites. A third experiment was carried out to test the effectiveness of MBZ included in the baseline diet of M. liza. The tested concentrations were: 0, 0.125, 0.25, 0.5 and 1g MBZ/200g ration.There was no significant difference between the 9 treatments in relation to the control, nor between the treatments (p <0.05). The T5 treatment (1g MBZ/200g) showed the highest percentage (97.9%) of effectiveness against Ligophorus sp., But this concentration was not effective in the treatment of Solostamenides sp. and Digenea. The highest efficacy percentages for Solostamenides sp. and Digenea were observed in T4 (0.5g MBZ/200g) being 100 and 53.3%, respectively. There were no histological changes in fish related to the use of MBZ in the diet. It appears that the effectiveness of MBZ varies, among other factors, between parasitic species, the concentration administered and the time of exposure. New studies verifying the analysis of palatability and exposure of the same concentrations for a longer period should confirm whether or not there is an improvement in the effectiveness of MBZ for Mugil liza.