Resumption and progression of meiosis and circulating levels of steroids and prostaglandin F _2α of Piaractus mesopotamicus induced by hypophysation with prostaglandin F _2α

Abstract

We have previously shown an increase on the ovulation rate of pacu, Piaractus mesopotamicus, using hypophysation with prostaglandin F2α (PGF2α) (HPG protocol) rather than hypophysation (H); only, however, a persistent lack of ovulation in some females could not be further explained by PGF2α and steroid plasma levels at time of ovulation. Considering this, here we compared the meiotic process and steroids and PGF2α levels during spawning induction using both protocols. To that, H and HPG were treated with conventional hypophysation (0.6 mg/kg priming and 5.4 mg/kg resolving dose), and the latter received synthetic PGF2α (2 mL/fish) at resolving dose. A negative control (saline solution), a SPG group (receiving only PGF2α) and a PPG group (receiving priming and PGF2α) were included. An initial PGF2α peak between one to four hours post‐resolving dose (1‐4 hr) occurred in groups receiving PGF2α (HPG, SPG and PPG). Only H and HPG showed a 17α‐20β‐dihydroxy‐4‐pregnen‐3‐one (DHP) peak 4 hr, concomitant with meiosis resumption, and a final PGF2α peak 12 hours. The HPG protocol resulted in higher PGF2α plasma levels for longer periods (1‐4 and 12 hr) than H (single peak 12 hr), occasioning in the former higher and concomitant levels of both PGF2α and DHP at 4 h. Considering that DHP is known to induce expression of prostaglandin receptors in fish, the concomitant plasma peaks of DHP and PGF2α may also explain the ovulation rate gain previously published, using HPG protocol, which can be further improved adjusting the priming dose and defining the exact interval of PGF2α ovulatory action in this species.

Spawning induction for Latin American fishes

“…For these species, the captive environment does not provide the correct cues for reproduction to progress through to spawning and this situation has been described as a reproductive dysfunction cause by the captive environment. Several captivity‐induced reproductive dysfunctions have been described in females and these were classified into three types in relation to the progress of gametogenesis, oocyte maturation, ovulation and spontaneous spawning 11,74,78–82 . Type 1 dysfunction is when oogenesis is arrested in the early stages before or as vitellogenesis initiates.…”

“…Hormone treatments appear to be a viable solution to induce ovulation/spawning in captivity and produce the eggs, larvae and fry necessary for aquaculture. However, reliable hormone induction treatments have not been developed for these LA species, despite of studies that identify the requirement of hormone‐induced spawning and test hormone treatments that include hypophysation, Gth and GnRHa based treatments for a range of species (see Tables 1, 2 and 3), such as such as P. mesopotamicus, 82 Leporinus friderici 80 and Astyanax altiparanae 133 …”

“…Hormone treatments appear to be a viable solution to induce ovulation/spawning in captivity and produce the eggs, larvae and fry necessary for aquaculture. However, reliable hormone induction treatments have not been developed for these LA species, despite of studies that identify the requirement of hormone-induced spawning and test hormone treatments that include hypophysation, Gth and GnRHa based treatments for a range of species (see Tables 1, 2 and 3), such as such as P. mesopotamicus, 82 Leporinus friderici 80 and Astyanax altiparanae. 133 Migratory species such as the C. macropomun are usually induced with the same standardized CPE protocol of 5.5 mg kg -1 body weight, in two applications (10% and 90%, with a 12-h interval between applications) of fractionated doses of pituitary extracts, which have been used for many years.…”

The environmental licensing of hydroelectrics and the interface with migratory fish and aquaculture in Brazil

“…Moreover, some Brazilian migratory fish species still do not have safe and totally predictable protocols for producing fingerlings (Sato et al, 2020). Regardless of the protocol employed, the reproduction of pacu, for instance, in captivity shows flaws in ovulation, which is one of the main limitations for its production (Criscuolo-Urbinati et al, 2012;Schorer et al, 2016;Kuradomi and Batlouni, 2018).…”

Piaractus mesopotamicus gonad differentiation

“…In Brazil, the production of pacu has remained stable between 10 and 15 thousand tonnes in recent years (IBGE, 2019). Several aspects of its production were recently improved to obtain a technological package that ensures its safe production, such as the development of improved strains (Mastrochirico‐Filho et al, 2020) and captive‐breeding protocols such as more assertiveness (Kuradomi & Batlouni, 2018; Sato et al, 2020). However, an aspect of its production that can make it even more attractive to farmers and can definitely consolidate its exploitation is the development of strains with better growth rates, given the short time of warm months in tropical and subtropical regions (approximately 6 months between spring and summer).…”