Cryopreservation of Sperm of the Endangered Gila Trout, Oncorhynchus gilae

Abstract

ABSTRACT Gila trout, Oncorhynchus gilae, are native to the headwaters of the Gila River drainage in New Mexico and Arizona and the headwaters of the Verde River drainage in Arizona. The species is currently protected as endangered under the Endangered Species Act. Cryopreservation of sperm is now a widely used method for long-term storage of fish semen. It is an effective tool for conserving genetic diversity in threatened and endangered species, and can also be used for genetic improvement through selective breeding programs. However, there is no one protocol that seems to work with all species offish. To determine the potential of this technique as a tool in the recovery of this endangered species, we sought to examine the effects of five cryoprotectants and four extenders of varying concentrations on post-thaw motility of Gila trout spermatozoa. Gila trout gametes were collected from broodstock located at Mora Fish Technology Center, Mora, New Mexico. We tested three extenders used successfully in other fish species to determine the most appropriate for use with Gila trout spermatozoa. Extender concentrations were tested to see at what osmolality there was no activation of spermatozoa. Five cryoprotectants were tested at varying concentrations to determine the most suitable for use with Gila trout spermatozoa. There was no significant difference (P < 0.05) in motility of Gila trout spermatozoa exposed to different extenders. The concentration at which no spermatozoa were observed actively swimming was 453 mOsm/kg calcium-free Hanks' Balanced Salt Solution. There was no significant difference (P < 0.05) in toxic effect or post-thaw motility among the different cryoprotectants or concentrations due to high motility variation between individuals. However, 9% dimethyl-sulfoxide yielded consistently higher mean post-thaw motility (23%). Larger sample sizes might be able to reduce the amount of intra-treatment variation, which will allow us to determine whether DMSO offers superior protection for Gila trout spermatozoa.