Deformidades morfológicas na fase embrio-larval de Rhamdia quelen (Teleostei) submetidos ao herbicida 2,4-d e ao extrato botânico de mamona

Abstract

The indiscriminate use of pesticides to combat weeds and other agricultural pests has increased negative impacts on the environment and non­target organisms. Aiming to minimize the effects caused, researchers have dedicated themselves to study natural products as an alternative method for pest control, with the development of plant extracts. However, it is necessary to evaluate not only synthetic chemical products but also the biosafety of alternative products in non­target organisms, being the initial stages of development an excellent strategy. Therefore, the objective of this work was to characterize the morphological deformities in the embryo­larval stage of Rhamdiaquelensubmitted to low concentrations of the synthetic herbicide2,4­D and the botanical extract of castor bean. Fertilized eggs were purchased from a commercial fish farm and exposed to test substances for 48 and 96 hpf (hours after fertilization). For the bioassays, the botanical castor bean extract was diluted in dimethylsulfoxide (1.0%) and later in reconstituted water, at concentrations of 50%, 25%, 12.5%, 6.25% and 3.12% of the LC50 previously determined for the target organism Chrysodexis includens (soybean caterpillar) and negative and vehicle controls. The 2,4­D herbicide was prepared at concentrations of 0, 15, 30 and 60 μg/L in reconstituted water. Both experiments were carried out on microplates, with controlled temperature and pH and with water change every 24 hours. Animals were anesthetized and sacrificed with eugenol. After each sampling time, the qualitative and quantitative analysis of the morphological deformities in the larvae of the species was performed. Deformities were classified according to the category and types of axial, fin, craniofacial and thoracic­abdominal damage,and the frequency of individuals with and without damage was subsequently analyzed using the chi­square test. Based on the results obtained, it was possible to verify that the 2,4­D herbicide and the botanical extract induced changes in the morphology of the larvae, mainly axial and fin for 2,4­D and craniofacial for the botanical extract. It is known that these changes can impair long­term survival, and also the perpetuation of the species.