Sperm characterization of the endangered Amazonian fish Hypancistrus zebra: Basic knowledge for reproduction and conservation strategies
Introduction
Brazil has one of the greatest biodiversity ecosystems on the planet, with more than 3000 known fish species, with the natural habitat of most being in the Amazon basin (Winemiller et al., 2017). This biodiversity has, however, been decreasing as a consequence of environmental changes. There has been a marked reduction in habitat for many fish species due to anthropic effects on the aquatic environment.
The growing energy demand in Brazil and its expansive water resources have resulted in the installation of hydroelectric projects. Damming interferes with the original river flow and affects the habitat of several species, causing habitat loss (Agostinho et al., 2008), modifying the capacity of fish to congregate (Barbosa et al., 2015) and negatively affecting reproduction (Röpke et al., 2017). In fact, the international scientific community is concerned about the future of aquatic biodiversity due to the large number of hydroelectric projects under construction and that are planned for establishment in the Amazon Basin (Lees et al., 2016; Latrubesse et al., 2017).
These detrimental factors affect the capacity for conservation of the zebra pleco Hypancistrus zebra (Isbrücker and Nijssen, 1991), a rare ornamental fish, endemic to the Xingu River (Pará State) occupying the lotic microhabitats in rocky outcrops (Lees et al., 2016). The relatively lesser fecundity of this as compared with many other fish species (Roman, 2011) and the mass illegal fishing for the international aquarium trade led to a significant population decrease, that resulted in placement of the H. zebra on the Brazilian Red List (ICMBio, 2016) as a critically endangered species. The species has also been added to the list of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES, 2016). The threat is even greater, especially due to the effect of the construction of the Belo Monte Hydroelectric Power Plant on the habitat for this species. The damages to the environment from this Power Plant enterprise are so severe that Belo Monte has been considered one of the most controversial hydroelectric projects in the world (Lees et al., 2016).
Given the circumstances, ex situ conservation may be the only alternative to avoid the extinction of this species. Although there have been some captive-born offspring (Ramos et al., 2016), reproduction in captivity has been inconsistent, which contributes to a lack of capacity in controlling reproduction in this species. Having high-quality gametes is very important for reproductive success in fish (Bobe and Labbé, 2010). H. zebra gametes have never been evaluated and it is not known whether captive animals will have the capacity to produce viable sperm. Knowing the seminal quality is the first consideration for standardization for in vitro manipulation and for development of semen storage protocols. In the present study, the aim was to characterize H. zebra semen and to assess semen quality throughout the year after successive stripping.
Section snippets
Fish care and permits
Adult Hypancistrus zebra were kept at a 0.5 g/l stocking density in 140 l aquariums. Each aquarium had three ceramic caves (3.5 cm diameter x19 cm depth) and two ceramic bricks with eight holes of the same size. Fish were fed commercial dry food (Tetra Color Bits™ and Sera Granulat™) and a laboratory produced semi-solid diet containing: 43.2% fresh sardine, 24% boiled carrot, 20.4% peeled shrimp, 8.04% boiled collard greens, 2.87% flavorless gelatin, 0.96% garlic, 0.24% vitamin supplement,
Sperm motility, sperm vigor and duration of sustained motility
There was semen collection four times during the year with there being similar (P > 0.05) quality for all sperm variables throughout the year (Table 1). Semen of Hypancistrus zebra had an average motility rate of 88.60 ± 2.49% (P = 0.6724), sperm vigor of 3.00 ± 0.13 (P = 0.8091), membrane integrity rate of 87.93 ± 1.88% (P = 0.0580) and duration of sustained motility of 14.72 ± 1.31 min (P = 0.4099).
The motility rate decreased 55% in the first 5 min after sperm activation (Fig. 2). After
Discussion
Based on results of the present study, it is possible to collect semen with viable sperm cells from H. zebra throughout the year. In addition, there was confirmation that the sperm quality is preserved after successive stripping. There are peculiar sperm motility characteristics for the species, with an intermediate sperm vigor and a longer duration of sustained motility than occurs in sperm of many freshwater fish species, suggesting that the slower flagellar movement allows for energy
Acknowledgments
J. Caldas was granted a PhD scholarship from the Research Support Foundation of Amazonas State (FAPEAM). L. Godoy is a research fellow from the Brazilian National Council for Scientific and Technological Development (CNPq 302999/2015-9). We thank Nilton Lins University and the National Institute of Amazonian Research (INPA) for providing the facilities to conduct this research. Special thanks to Dr. Ligia Gonçalves for encouraging this study and to Dr. Jansen Zuanon for donating the fish.
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