Sperm quality assessments for endangered razorback suckers Xyrauchen texanus.

Flow cytometry (FCM) and computer-assisted sperm motion analysis (CASA) methods were developed and validated for use with endangered razorback suckers Xyrauchen texanus collected (n=64) during the 2006 spawning season. Sperm motility could be activated within osmolality ranges noted during milt collections (here 167-343 mOsm/kg). We hypothesized that sperm quality of milt collected into isoosmotic (302 mOsm/kg) or hyperosmotic (500 mOsm/kg) Hanks' balanced salt solution would not differ. Pre-freeze viabilities were similar between osmolalities (79% +/- 6 (S.E.M.) and 76% +/- 7); however, post-thaw values were greater in hyperosmotic buffer (27% +/- 3 and 12% +/- 2; P=0.0065), as was mitochondrial membrane potential (33% +/- 4 and 13% +/- 2; P=0.0048). Visual estimates of pre-freeze motility correlated with total (r=0.7589; range 23-82%) and progressive motility (r=0.7449) by CASA and were associated with greater viability (r=0.5985; P < 0.0001). Count (FCM) was negatively correlated with post-thaw viability (r= -0.83; P=0.0116) and mitochondrial function (r= -0.91; P=0.0016). By FCM-based assessments of DNA integrity, whereby increased fluorochrome binding indicated more fragmentation, higher levels were negatively correlated with count (r= -0.77; P < 0.0001) and pre-freeze viabilities (r= -0.66; P=0.0004). Fragmentation was higher in isotonic buffer (P=0.0234). To increase reproductive capacity of natural populations, the strategy and protocols developed can serve as a template for use with other imperiled fish species, biomonitoring, and genome banking. Reproduction (2011) 141 55-65