Lipid droplet distribution in Atlantic salmon (Salmo salar L.) oocytes is related to the fertilisation and developmental outcome

At present, there is no simple and practical applicable method to determine the quality of Atlantic salmon oocytes upon collection at the fish farm. Investigating oocyte lipid droplet patterns might be a tool for the aquaculture industry to predict oocyte quality in Atlantic salmon. While examining the lipid distribution in oocyte batches from 16 females of Atlantic salmon with a range in fertilisation rate (6–97 %), five categories of lipid droplet patterns were distinguished. In category 1, the lipid droplets were evenly distributed whereas in the remaining categories lipid droplets showed varying degree of coalescence. Categories 2, 3, 4 and 5 were distinguished based on the area of coalesced lipid droplets. The fertilisation rate was observed to be high (≥ 90 %), in females that had more oocytes from category 1, 2 and 3 whereas females with more oocytes from category 4 and 5 showed a low fertilisation rate (<90 %). A similar pattern was revealed between lipid droplet categories and eyed embryo and hatching success. Staining of salmon oocytes further confirmed the observed lipid droplet patterns, and different sizes of lipid droplets were present in almost all oocytes. The study revealed a significant association between lipid droplet category and fertilisation outcome in oocytes of Atlantic salmon that can be a practical tool for predicting oocyte quality. • Oocyte lipid droplet distribution is predictive of fertilisation in Atlantic Salmon. • Lipid droplet patterns are associated with embryo survival and hatching. • A novel method with five categories of oocyte lipid distribution was established.