FERTILITY EVALUATION OF THE TAMBACU HYBRID (Colossoma macropomum × Piaractus mesopotamicus) AT THE THREE YEARS OF AGE
The crossbreeding between the female tambaqui (Colossoma macropomum ) and the male pacu (Piaractus mesopotamicus ) is a production strategy widely used by fish farms in tropical regions of South America, because the hybrid Tambacu gathers the good growth traits of tambaqui with the resistance to low temperatures of pacu . However, the possibility of this hybrid being fertile places the wild populations at risk, because genetic introgressions can occur and can result in the extinction of one of the parents. We compared the fertility of the Tambacu hybrid with the purebreed pacu species by evaluating animals up to three years of age.
Two genetic groups, pacu (1.0 ± 0.138 kg) and tambacu hybrids (1.3 ± 0.136 kg), stored in 600 m2 ponds with densities of 1 fish per 6 m², were evaluated. These animals were generated from mates performed during the breeding season of 2015/2016 using breeders from Aquaculture C enter of UNESP, Jaboticabal, SP/ BR, previously evaluated by means of molecular techniques (PCR Multiplex and PCR-RFLP), confirming which were actually of pure parent species. From september 2017, four samples were taken (22/09/2017 - spring; 17/01/2018 - summer; 05/04/2018 - autumn; and 22/10/2018 - spring). At each date, five animals of each group were sampled, weighed, slaughtered and dissected to obtain weights of the gonads (Wg ) and liver (Wl). With the data collected, the gonadossomatic (IGS) and hepatosomatic (HSI) indexes were calculated. In the reproductive period of 2018/2019, animals from both genetic groups were induced with hormone to verify if they were able to produce viable gametes.
The parameters obtained during the fourth evaluation indicated that only pure animals presented gonadal development up to the third year of age (Table 1). In addition , only the fish of pacu group responded to hormonal induction and produced viable gametes.
Financial support: FAPESP (2018/16765-0)
