Cryopreservation of yamú ( Brycon amazonicus) sperm for large scale fertilization

To determine the effect of straw size and thawing temperature on cryopreserved sperm quality of yamú ( Brycon amazonicus), ovulation and spermiation were induced in sexually mature broodstock using Carp Pituitary Extract. Sperm quality was evaluated by motility, activation time and fertility. Sperm was diluted (1:4) in a solution of glucose, egg yolk and dimethyl sulfoxide (DMSO). Sperm concentration was determined using a Neubauer chamber, and motility evaluated after activation with 1% NaHCO 3. In the laboratory, four sizes of straw (0.5, 1.8, 2.5 and 4.0 mL) and two thawing temperatures (35 °C or 80 °C water bath) were evaluated. To assess fertility, 2 g of eggs (ca. 2800) were inseminated with 500 μL of frozen-thawed sperm (ca. 75,000 motile spermatozoa/egg) from each straw thawed at 35 °C or 80 °C, or 160 μL (ca. 50,000 motile spermatozoa/egg) of fresh sperm. Large scale fertility assays consisted of 40 g eggs inseminated with approximately 5.0 mL (ca. 75,000 motile spermatozoa/egg) of cryopreserved sperm in large straws thawed at 35 °C. The fertilization rate was estimated 6 h post-insemination. In all straws, post-thaw motility was significantly lower than for fresh sperm ( p < 0.05). In laboratory trials, fertility of fresh sperm was higher (67 ± 4%) than frozen-thawed sperm ( p < 0.05). For all types of straw, semen thawed at 35 °C had a higher percentage of fertility ( p < 0.05) than semen thawed at 80 °C; sperm cryopreserved in 1.8-, 2.5- and 4.0-mL straws had similar fertility percentages ( p > 0.05) to sperm frozen in 0.5-mL straws (48 ± 2%, 51 ± 2%, 52 ± 2% and 54 ± 3%, respectively). In large scale fertilization trials, fresh sperm showed a higher ( p < 0.05) fertilization rate (83 ± 1%) than frozen-thawed sperm (68 ± 1%). Although the fertility percentage with fresh sperm was significantly higher than with frozen-thawed sperm in large straws, the fertilization rate of the latter is considered acceptable and profitable in a commercial setting.