Seminal Cryopreservation of bagre rayado Pseudoplatystoma metaense (Teleostei, Pimelodidae), under different protocols of freezing

Abstract

The aim was to determine the effect of different extenders and freezing rates on bagre rayado seminal quality. Sexually mature males (1.5 ± 0.2 kg and 56.6 ± 2.9 cm) and females (2.8 ± 0.7 kg and 71.3 ± 6.1 cm) were used. Ovulation and spermiation were induced with Carp Pituitary Extract. The semen was diluted (1:6, semen: diluent) with a glucose-based solution (5.5%) and egg yolk (YH, 12%) or whole milk powder (LE, 5%). As cryoprotectants dimethyl sulfoxide (DMSO, 10%), methanol (MET, 12%) or dimethyl acetamide (DMA, 10%) were used. The diluted semen was packaged in 0.5 mL straws and frozen in two freezing curves (C1= 2.4 °C·min^-1 from 28 to -4 °C, followed by 10.0 °C·min^-1 from -4 to -80 °C and C2= 8.4 °C·min^-1 of 4 to -80 °C) and then immersed in liquid nitrogen (-196 °C). The straws were thawed in a water bath at 35 °C by 60 sec and immediately assessed motility. The fertility was assessed through semination of 2 grams of oocytes with 100 or 400 µL of fresh or frozen semen, respectively, and determined at 6:00 h postfertilization. The results showed higher rates of fertility with fresh semen, fertilized oocytes were observed in all treatments, with greater percentage (greater than 60%) from the semen under the C2 (greater than 60%) and 10 or 12% of DMSO or MET, respectively and 5.5% glucose and 5% of LE. These results allow to establish an acceptable freezing protocol for the artificial reproduction of bagre rayado.