The effects of cryoprotectants on chilled pirapitinga (Piaractus brachypomus) embryos at various ontogenetic stages

Cryopreservation has not been successfully used to preserve fish embryos, although chilling techniques have been used with good results. The aim of this study was to chill Piaractus brachypomus embryos at different stages of development in some cryoprotectants and for various periods of chilling. Embryos at the following ontogenetic stages were used: blastoderm – 1.2 hours post-fertilization (hpf); epiboly – 5 hpf; blastopore closure – 8 hpf; and appearance of optic vesicle – 13 hpf. One hundred embryos were selected from each of the four stages and chilled in methanol, methylglycol or dimethylsulfoxide (DMSO) for 6, 8, 10 or 12 hours, at 2ºC. The total number of treatments was 4 stages x 3 cryoprotectants x 4 periods of chilling. The highest percentage of normal and live larvae (30.6%) was observed when embryos were chilled at 13-hpf in methanol for 6 hours. In general, larvae chilled at a more developed stages (8 and 13 hpf), in methanol and for shorter periods could survive chilling and develop normally, compared to the other treatments. Therefore, P. brachypomus embryos at the optical vesicle appearance stage (13 hpf) should be chilled in a solution containing 17.5% glucose and 10% methanol for up to eight six at 2°C