POST-COOLING DAMAGE TO Piaractus mesopotamicus EMBRYOS AT DIFFERENT STAGES OF DEVELOPMENT

The present study investigated the effects of 6h- and 10h-storage at -8oC on the quality and hatch rate of Piaractus mesopotamicus embryos at 4 stages of development. Embryos were exposed to a cryoprotectant solution, cooled down at a rate of 1oC.min -1 to -8oC, and stored at this temperature for 6h and 10h, respectively. For control treatment, viable embryos at the 4 developmental stages studied, were selected and taken immediately to the incubator, without going through cooling. The results were evaluated using a multivariate statistical technique (factor analysis). Damage was characterized according to the following variables: uniformity, adhesion, symmetry, margins, and inclusion. Two factors that best explained the variance of each parameter were defined. The control group had the highest hatch rates, and a weak relationship with embryo damage. Although treatments involving 6h and 10h cooling exhibited lower hatch rates and a higher association to damage. The information obtained in this study is useful in promoting improved cryopreservation techniques for fish embryos, indicating the probable conditions under which certain injuries are more frequent. Keywords: cryopreservation, embryogenesis, multivariate analysis, South American fish