Effects of hormonal treatment on induced spermiation and semen quality in the endangered Amazonian fish Hypancistrus zebra (Siluriformes, Loricariidae)

Abstract

Reproduction in fish is influenced by several environmental factors. In many cases, failure in reproduction is common once fish are no longer in their natural habitat. Thus, the use of exogenous hormones has been crucial to control the reproductive cycle of many fish species under ex situ conditions. These hormonal stimulations became yet more important for those species facing extinction, as the case of Hypancistrus zebra. Since its habitat has been destroyed, successful reproduction in captivity is a way to ensure species survival. The first phase of this study aimed to test the possibility of getting semen from Hypancistrus zebra without hormonal induction. Two groups of fish (24 each) were subjected to two treatments: hormonal induction with 3 mg kg−1 CPH (carp pituitary homogenate) and spermiation without hormonal induction. In the second phase, was evaluated the effect of hormonal induction on semen quality using gonadorelin (a GnRH synthetic analogue) at doses of 40, 60, 80, 100 and 120 μg kg−1. CPH treatment was used as a positive control and one group of fish was not induced (negative control). Collected semen was assessed for volume, sperm concentration, motility rate, sperm vigor, duration of motility, membrane integrity and spermatozoa morphology. We were able to successfully collect semen from the endangered Hypancistrus zebra without hormonal induction, however when subjected to the hormonal treatment males released a higher volume of semen, with higher quality in some parameters. CPH treatment was more efficient in improving sperm quality in H. zebra, favoring normal sperm morphology, although gonadorelin did not harm it. The minimum effective dose of gonadorelin to increase seminal volume is 100 μg kg−1, which can be applied in a single injection. Information gained from this study will assist semen collection procedures for a germplasm bank formation and other initiatives for conservation of this Amazonian endangered fish species.