Avaliação da segurança terapêutica do formol em larvas e juvenis de Pacamã (Lophiosilurus alexandri)

Abstract

The stage of larviculture is considered one of the most critical phases in the production of fish, and it is necessary to develop adequate management for success in the production of fish. With intensification, larviculture can be affected by diseases and parasitic diseases resulting from poor water quality, as well as animal stress, making them more susceptible to them. Parasites are important in fish farming because they cause economic losses to producers, as they can cause poor performance or even mortality. There are prophylactic and therapeutic treatments with chemicals that are performed by immersion baths. Among the most used, formaldehyde is shown to be effective in the prophylaxis and treatment of ectoparasites. However, it is necessary to perform toxicity tests that will show the ideal dose that does not harm the development of the animal, which may be species-specific, and be influenced, also, by factors such as age and sex. The objective of this study was to evaluate the acute toxicity, pathological changes and level of therapeutic safety of formalin in larvae and juveniles of Lophiosilurus alexandri. Three experiments were carried out at different ages. Experiment 1, larvae with a mean weight of 0.021 ± 0.003 g were submitted to concentrations 43.2; 86.4; 172.8; 345.6; 691.2 and 1404.0 mg L-1 of formaldehyde, in addition to the control (without addition of formalin). In experiment 2, juveniles with a mean weight of 0.23 ± 0.03 g were submitted to concentrations of 54.0; 108.0; 216.0; 432.0 and 648.0 mg L-1 formaldehyde plus the control. Already, in experiment 3, juveniles thinking on average 3.75 ± 0.81 g were submitted to concentrations 86.4; 172.8; 345.6; 691.2 and 1036.8 mg L-1 formaldehyde and control. The 12-hour LC50 for experiment 1 was 108.86 mg L-1 with a confidence interval (CI) of 99.06 to 119.63 mg L-1, in experiment 2 it was 152.74 mg L-1 with CI between 142.62 - 156.18 mg L-1 and for experiment 3, 244.38 mg L-1 and IC between 224.37 - 251.23 mg L-1 of formaldehyde. Juveniles exposed to increasing concentrations of formaldehyde presented severe pathological changes in the gills, among them secondary lamella hyperplasias, epithelial detachment, lamellar fusion and telangiectasia. It can be verified that animals of experiment 2 suffered more changes in the gills when compared to the animals of experiment 3. It is concluded that the age and stage of development influences the sensitivity of the animals in relation to the exposure of the formalin