Oocyte quality indicators in Eurasian perch, Perca fluviatilis L., during reproduction under controlled conditions

This study examined embryo survival and viability of Eurasian perch, Perca fluviatilis L., larvae in relation to the fragmentation of oil droplets in ovulated oocytes. The study was conducted after controlled reproduction. Four (I–IV) categories of egg-ribbons quality were distinguished, based on the degree of oil droplet fragmentation (where at least one oil droplet with minimum 0.39 mm diameter were certified in all oocytes in egg-ribbon — categories I and II) and percentage of eggs with highly fragmented oil droplets (where diameter of oil droplets did not exceed 0.35 mm — categories III and IV) in the egg-ribbon. The dynamics of survival and some morphological parameters were investigated during embryonic and larval development up to 10 days post-hatch (DPH), under laboratory conditions. The laboratory-obtained results were compared to semi-commercial incubation and initial larval rearing. The fragmentation of oil droplets was accompanied by a decrease in egg quality. Oil droplets were found to coalesce after activation of eggs in water and during incubation process. Thus, the presented categorization may be used in non-activated eggs only. In both experiments, at 10 DPH the percentages of feeding larvae and those with an inflated swim bladder were recorded. The best results of laboratory-conducted incubation were obtained in category I and II (92.80 and 74.20% in the eyed-egg stage respectively). In category IV, the mortality rate of embryos exceeded 90%. The highest body deformation rate of freshly hatched larvae was observed in category III (67.86%) and IV (86.14%) that was related with fragmentation of oil droplets. These results were confirmed under semi-commercial conditions. The obtained results indicate that the proposed categorization may be a valuable tool for the quality evaluation of Eurasian perch egg-ribbons. It could be successfully applied in both commercial fish production and scientific activity.