The fertilization efficiency of cryopreserved sperm was compared with fresh sperm from striped catfish, Pangasius hypophthalmus. Of the two sets of experiments carried out, the first compared four sperm doses using fresh sperm and fresh eggs. The second experiment compared six concentrations of cryopreserved sperm ranging from 6.94 x 107 to 6.94 x 1010 to fertilize100 eggs per batch. Fertilization, hatch and survival rates were compared between cryopreserved and fresh sperm. The highest fertilization rate (53.75 x 1.62 %) was achieved with a sperm dose of 6.94 x 108. Increasing the sperm dose to 3.47 x 109 did not increase the fertilization rate, indicating that the optimum sperm:egg ratio lies between 6.94 x 106 and 3.47 x 107 sperm per egg. Both high- est (6.94 x 1010) and the lowest (6.94 x 107) sperm doses resulted in lower fertilization rates (2.04% and 16.90% respectively). No significant differences were found among four fresh sperm doses compared. Mean hatch and survival rates resulting from fresh and cryopreserved sperm were similar. The experiment shows that while only 1.89 x 106 fresh spermatozoa was required to fertilize a fresh egg, 6.94 x 106 (or 3.67 times more) cryopreserved sperm was required to achieve the same level of fertilization. This provides important information for making decision to cryopreserve sperm for commercial and/or conservation purposes.
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