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% NaHCO3. 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.