Abstract

The Orinoco Striped Catfish Pseudoplatystoma orinocoense is a highly valued commercial-capture species in Colombia. Although this species was considered endangered and is now in a recovery situation, there are still no cryopreservation studies for its milt. Therefore, the objective of this study was to evaluate the effects of different cryopreservation media and two packaging systems on the sperm motility and fertilization capacity of Striped Catfish. A first experiment was conducted to test the effects of two permeating cryoprotectants (10% dimethyl sulfoxide and 12% methanol) combined with glucose at two concentrations (5.5% and 10%) and with two membrane stabilizers (12% egg yolk and 5% whole milk powder) on the post-thaw motility of milt samples that were packed into 0.5-mL straws. The cryopreservation media with the best results in the first experiment were selected for a second experiment in which we evaluated 5-mL macrotubes as a packaging system. In this case, the response variables were sperm motility and fertility rate. In both experiments, milt with sperm motility that exceeded 90% was diluted at a 1:6 (volume basis) ratio in each of the two cryopreservation media. The diluted samples were packed, equilibrated (for 10 min), then frozen in a nitrogen-vapor dry shipper for 30 min, and finally stored in liquid nitrogen until they were evaluated. Each factor and its interactions showed a significant effect (P < 0.001) on post-thaw sperm motility in experiment 1. The best protection during cryopreservation was obtained when 12% methanol supplemented with 5.5% glucose was used as a permeating cryoprotectant, yielding an average motility of 33.3 +/- 5.1% (mean +/- SD) and 64 +/- 5.4% in the 0.5- and 5-mL packaging systems, respectively. Similarly, the highest fertility rate (85%) was recorded under this treatment, with no significant difference (P > 0.05) from the fresh milt. Therefore, Striped Catfish milt can be cryopreserved in 5-mL macrotubes by using 12% methanol and 5.5% glucose, without the addition of membrane stabilizers.