Effects on fertility of motile sperm to egg ratio with use of cryopreserved Rhamdia quelen semen at different post-activation times

Abstract

The aim in the present study was to evaluate the effects of motile sperm:oocyte ratio and the use of thawed spermatozoa at different post-activation times in artificial reproduction of gray catfish (Rhamdia quelen). Cryopreserved sperm samples were evaluated for sperm motility and velocity using Computer Assisted Sperm Analysis (CASA). The sperm activation curves were generated using a non-linear statistical model and were used to assess the spermatozoa velocity after thawing. Thus, the oocytes were mixed with thawed sperm at a motile sperm:oocyte ratio of 70,000, 90,000, 110,000, 130,000, 150,000 and 170,000. The thawed sperm were used at 11, 16 and 30 s after spermatozoa activation. At these times, the sperm velocities corresponded to 52, 37 and 21 μm/s. The effects of experimental factors (spermatozoa:oocyte ratio and time after sperm activation) on oocyte fertilization, egg hatching, and percentage of normal larvae were evaluated. The response surface analysis indicated there was no interaction (P > 0.05) between the motile spermatozoa:oocyte ratio and time after sperm activation on fertilization, hatching or percentage of normal larvae. The time after sperm activation, however, affected (P < 0.05) in a directly proportional waythe oocyte fertilization and egg hatching rates. The time after sperm activation affected the sperm velocity and oocyte fertilization and egg hatching rates. Thus, the use of thawed sperm immediately after sperm activation or with the greatest sperm velocities (11s; 52 μm/s; 62.59% motility) at a relatively lesser motile sperm:oocyte ratio (70,000:1) allows for acceptable fertilization (48.68% for fertilization; 29.61% for hatching) in Rhamdia quelen.