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Godoy et al. wrote:

Hypancistrus zebra

is an endemic fish to the Xingu River (Brazilian Amazon) and is critically endangered by the construction of a hydroelectric plant in its habitat and illegal fishing. In an attempt to establish a germplasm bank and preserve the species, this work aimed to test the efficiency of the cryoprotectants dimethylsulfoxide (Me2SO) and methanol in the semen freezing process. The semen of each three fish group (total = 24) was fresh evaluated, pooled together and diluted in Hanks' Balanced Salt Solution (HBSS) containing the cryoprotectants Me2SO and methanol at 10% concentration. Semen was loaded into 0.25 mL plastic straws, equilibrated for 5 minutes at room temperature (20 °C) and stored in a dry shipper for 4 hours. The samples were then transferred to a liquid nitrogen dewar and stored for 24 h. Thawing was performed using a water bath at 40 °C for 8 s and thereafter diluted (1: 1 / v: v) in HBSS. Fresh and thawed semen were assessed for motility rate and for membrane integrity by using vital staining with eosin-nigrosin. Fresh sperm had a motility rate of 91.0 ± 11.0% and 90.25 ± 4.39% of the spermatozoa had intact membrane. The frozen-thawed semen showed a motility rate of 18.0 ± 16.4% and membrane integrity of 34,6 ± 7,8 % in Me2SO and in methanol 2,2 ± 4.4 % and 30,4 ± 15,6 respectively. Preliminary results indicate that H. zebra spermatozoa are very sensitive to low temperature exposure and dimethylsulfoxide was more efficient than methanol in protecting them from cryoinjuries. The attempt in freezing the semen of this rare and endangered ornamental fish species is described here for the first time. Our studies are underway to optimize the freezing protocol and to create a germplasm bank for the species.