Piaractus mesopotamicus gonad differentiation

Abstract

In this study, we evaluated the pacu (Piaractus mesopotamicus) gonadal differentiation process from zero to 299 days after eclosion (DAE). To that end, individuals were subjected to 5 samplings (96, 123, 150, 233 and 299 DAE) for evaluation of the gonadal differentiation process through histological analysis. The gonads were recognized macroscopically from 96 DAE and were undifferentiated up to 123 DAE. Differentiation into ovaries was first observed at the 150 DAE sampling (average total length = 10.03 ± 0.12 cm and average total biomass = 18.21 ± 1.22 g). We observed a great heterogeneity of sizes in the fish analysed up to 299 days. At the end of the experiment, only 11/51 animals analysed had gonads differentiated into ovaries, and the process occurred in a large window. Sex differentiation into testis was not observed.This study also showed that larger and more aggressive fingerlings that occupied the front part of earthen ponds, popularly known in Portuguese as cabeceiras, were not necessarily females, as previously believed due to their larger size. Thus, we did not observe sexual dimorphism up to 299 DAE, but since it is known that in adult females of this species do reach larger sizes, future approaches need to show whether differentiated growth rates between genera occur before slaughter size, thus justifying the production of single-sex populations.

Effect of temperature on gonadal differentiation and growth of Leporinus friderici

“…The process of transitioning from undifferentiated gonads to ovaries (150 DAE) occurred earlier compared to the differentiation to testes (190 DAE). The observed pattern of differentiation observed in this study, where differentiation into ovaries occurs before differentiation into testes, is consistent with what has been commonly described in the majority of Neotropical fish species such as piracanjuba ( Brycon orbignyanus ) ( Zardo et al, 2021 ; Quirino et al, 2022 ), pacu ( Piaractus mesopotamicus ) ( Barbosa et al, 2022 ), lambari ( Astyanax altiparanae ) ( Adolfi et al, 2015 ) and pirarucu ( Arapaima gigas ) ( Amaral et al, 2020 ). The differentiation process was initiated at 150 DAE at 25 °C and at 170 DAE at 29 °C.…”

“…So, it seems that growing rates are not necessarily related to sex differentiation in some migratory tropical fish used in aquaculture. Thus, unlike tilapia, where the growth differences between males and females are prominent before the harvest weight (reviewed in Taranger et al, 2010 ), for medium to large-sized migratory characiform fish such as P.mesopotamicus ( Barbosa et al, 2022 ) and L.friderici (present study) this issue remains to be elucidated.…”

“…In this aspect, a longer period of analysis would be necessary to identify any differences in growth rates between males and females that could justify the production of a monosex population. Intense differences in biometric data among specimens of same age before differentiation were found in another native migratory fish, P. mesopotamicus ( Barbosa et al, 2022 ). So, it seems that growing rates are not necessarily related to sex differentiation in some migratory tropical fish used in aquaculture.…”