A lack of consistent relationship between distribution of lipid droplets and egg quality in hatchery-raised rainbow trout, Oncorhynchus mykiss

The usefulness of lipid droplet distribution patterns for grading eggs of hatchery-raised rainbow trout, Oncorhynchus mykiss, was evaluated. Eggs from females of autumn (n = 29) and spring (n = 30) spawning were evaluated for distribution of lipid droplets and tested with a water turbidity test as well. Fertilization rates were measured in eyed-stage embryos, hatched-stage embryos and swim-up stage larvae. For both spawnings high fertilization rates were recorded, and lipid droplet distribution patterns were characteristic for good quality eggs. In the autumn spawning, the lipid droplet distribution pattern was significantly related to fertilization rates. Moreover, the differences in egg quality recorded at the eyed stage were more pronounced at hatching and swim-up stages. However, distribution of lipid droplets was not a useful parameter for the evaluation of egg quality in the spring spawning. The water turbidity test was not related to lipid droplet distribution. At present due to inconsistent results and the lack of understanding of this inconsistency, lipid droplet distribution for the evaluation of the quality of rainbow trout eggs must be used with caution. Our results suggest, that breeding and maintenance conditions influence lipid droplet distribution in salmonid eggs.