Chilling curves for Piaractus mesopotamicus (Holmberg, 1887) embryos stored at-8 degrees C
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The present study investigates the effect of different slow chilling curves on the storage of pacu (Piaractus mesopotamicus) embryos submitted to chilling at -8 degrees C. Embryos at the blastopore closure stage were divided into two groups: G1 - embryos exposed to cryoprotectant solution containing methanol (10%) and sucrose (0.5M), treated as follows: (T1) taken directly from room temperature to the refrigerator without being submitted to the curve; (T2) chilling curve of 0.5 degrees C/min; and (T3) chilling curve of 1 degrees C/min; and G2 - the cryoprotectant solution alone was submitted to these same temperatures, receiving the embryos only after temperature had decreased, corresponding to treatments T4, T5 and T6, respectively. Treatments were kept at -8 degrees C for a period of 6 h. Embryo development was evaluated for each treatment, with six replicates in an entirely randomized design. Survival among embryos not submitted to refrigeration was 94.3 +/- 8.05%. Percentage of total larvae (TL) and addled eggs (AE) did not differ statistically between the groups, although percentage of swimming larvae (SL) exhibited higher values in G1 for the 1 degrees C/min curve. Furthermore, when comparing the three chilling curves, a decrease of 1 degrees C/min resulted in the highest TL percentage (90.85%), followed by the 0.5.C/min curve (78.52%). Thus, the use of 1 degrees C/min chilling curves is recommended for P. mesopotamicus embryos stored for 6 h at -8 degrees C.