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.