Leporinus elongatus induced spawning using carp pituitary extract or mammalian GnRH analogue combined with dopamine receptor antagonists.

Thiago Scremin Boscolo Pereira,Camila Nomura Pereira Boscolo,Renata Guimarães Moreira,Sergio Ricardo Batlouni

doi:10.21451/1984-3143-2017-ar983

Abstract

Several studies have been developed to support the replacement of the crude carp pituitary extract (CPE) by synthetic products for induced reproduction of South American rheophilic species. However, results have been quite heterogeneous and there is no consensus or a routine use of synthetic products in these species. Thus, the aim of this study was to evaluate the ovulatory process in L. elongatus using different protocols of hormonal induction. Thus, fifteen wild mature females maintained at the Experimental Fish Station, Salto Grande, SP, Brazil were submitted to three different hormonal treatments: CPE (fractioned dose: 0.5 and 5.0 mg kg-1); mGnRHa (single dose: 3.5 µg kg-1) and mGnRHa (single dose: 5.0 µg kg-1). The spawning rate and absolute fecundity were similar among the treatments, but fertility rates were higher for CPE treatment (23.60 ± 9.40) then for mGnRHa treatments (close to or zero zero). Although females ovulated in all treatments, none of them provided viable embryos, showing hatching rates close to zero or zero. Both mGnRHa treatments were more potent for inducing the ovulatory process then CPE treatment, which was evidenced by the fact that the formers showed higher volume density of postovulatory follicles (POF). Accordingly, E2 and 17α-OHP plasma levels were higher for the mGnRHa treated females compared to the CPE one at the time of ovulation. In this study we confirmed previous scientific evidence that, regardless of whether promoting ovulation, the use of conventional CPE and GnRH doses are not appropriate for some South American migratory species, due to the non-attainment of viable embryos. Moreover, we have brought new information about the relationship between reproductive performance and gonadal steroids concentrations using different hormonal therapies, contributing to understand the reasons for Leporinus elongatus embryo loss in induced spawning.

Highlights

Leporinus elongatus is a medium-sized, total spawner rheophilic fish, commercially relevant and known to be a good model for studies concerning the reproductive biology of rheophilic species (Duke Energy International-Geração Paranapanema S/A., 2003)
We demonstrated that the treatments with low mGnRHa doses were more potent for inducing final maturation and ovulation in comparison with the conventional carp pituitary extracts (CPE) protocol, as evidenced by the statistically higher values of germinal vesicle break down (GVBD) and postovulatory follicles (POF) in post-spawning ovaries, as well as the higher gonadal steroid levels; none of the treatments provided viable embryos
The use of conventional doses of CPEs has already been shown to provide L. elongatus ovulation and viable embryos (Sato et al, 2000), the low embryo viability obtained in all treatments in the present study may be related to the use of different conditions and broodstock in each experiment, but mainly to the use of wild breeders

Summary

Introduction

Leporinus elongatus is a medium-sized, total spawner rheophilic fish, commercially relevant and known to be a good model for studies concerning the reproductive biology of rheophilic species (Duke Energy International-Geração Paranapanema S/A., 2003). When kept in captivity, even though they reach advanced stages of gonadal development, the final maturation and ovulation does not occur (Godinho, 2007; Makrakis et al, 2007; Brito and Carvalho, 2013) This rheophilic species needs to be hormonally induced for providing fingerlings under captivity conditions (Sato et al, 2000; Streit-Jr et al, 2008). In this concern, the use of Gonadotrophin releasing hormones analogues (GnRHa) has grown rapidly due to its numerous advantages, but mainly because they are not species-specific molecules and present high structural similarities among fish. The efficiencies of the use of synthetic products in some South American rheophilic species (Ittze’s et al, 2015; Viveiros et al, 2015) have already been shown - such as obtaining ovulation and viable embryos - and even if they sometimes have a higher potential for inducing ovulation compared to that of CPE (Pereira et al, 2017), the use of mGnRH in these species is frequently associated with ovulation failure (Carneiro and Mikos, 2008) and / or failure in obtaining viable embryos (Acuña and Rangel 2009; Paulino et al, 2011; Pereira et al, 2017)

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