In Paiche, Arapaima gigas, known as Pirarucu in
Brazil, no external characteristics are available to
distinguish sex. The special naked type ovary structure in this fish (gymnovarium) makes the canulation
impossible. In the Paiche, an obligatory air-breathing
fish, using anesthesia for fish manipulation is very
difficult because the risk of non-recovering the airbreathing reflex is very high. This prevents the use of
methods requiring the immobilization of the fish for
several minutes, like endoscopy or surgery