Determinação de sexo em tuviras (Gymnotus sp.) através de punção abdominal

Abstract

The large amount of rivers in Brazil has made possible an expressive increase in the sport fishing. The variety of used baits is massive, and the tuvira (Gymnotus sp.) is the living bait most used by fishermen in the capture of large carnivorous fish. Tuvira is a freshwater fish, belonging to the order of the Gymnotiformes, also known as: swordfish, sarapó, eel, ituí, morena, morenita and mamacha. It is found from South of Argentina to the North of Mexico. Its capture has a negative impact on the environment and causes concern to the working conditions of the people who carry out the extractive activity (bait men). Tuvira farming is still limited due to lack of an adequate protocol to perform of hormonal induction. In addition, the process of sexing in tuviras is difficult since they do not present sexual dimorphism. Thus, the aim of this study was to verify if the abdominal puncture could be used as a reliable technique to identify the sex of tuviras (Gymnotus sp.). Animals were collected between November 2016 and October 2017 in streams and dams located at Uruguaiana and Barra do Quaraí-RS cities. Eighty five individuals were collected and kept in concrete tanks of the Technology Centre of Fisheries and Aquaculture. Before performing the abdominal puncture, five individuals were dissected to determine the exact location of the gonads. Based on this information, the abdominal puncture was performed six centimeters away from the tip of the animal's head and 1 centimeter below the lateral line with an intravenous infusion set (number 19G) connected to a 5-mL syringe. The needle was introduced at an angle between 40º and 45º in relation to tuvira body. Abdominal puncture was performed in 24 adult animals that were larger than 20 cm in size. Twenty-two individuals were sexed correctly and the accuracy degree was 91.66%. The survival rate of the animals after 96 hours of abdominal puncture was 100%. These results indicate that abdominal puncture is an easy, simple and inexpensive technique and that it can be performed in a reliable way.