The presence of inclusions in blastodiscs of coho salmon embryos (Oncorhynchus kisutch) is associated with low rates of fertility and embryo survival

Abstract

Characteristics of the first blastomeres in fish have been evaluated in previous studies as a tool for predicting egg and larva quality. Nevertheless, there are still few studies of the presence of inclusions in fish blastodiscs or blastomeres. The object of the present study was to describe the relationship between cellular inclusions and some embryo quality parameters (symmetry, fertility rate, survival rate) in farmed coho salmon. Eggs from 261 females were fertilized with 400 × 10³ spermatozoa/egg and incubated in the dark in separated flow-through incubators. Embryos at the four-cell stage were fixed in Stockard's solution and the blastodiscs were classified as: i) unfertilized, ii) fertilized with inclusion, and iii) without inclusion. The blastomere symmetry was also recorded. Embryos from 30 females (15 with and 15 without inclusions) were incubated until pigmented eye embryo stage to determine the survival rate. Cell inclusions were detected in 8.81 % of the females evaluated, with 24.1 ± 24.2 of the eggs from each of those females presenting inclusions. Egg samples with this abnormality showed significantly lower fertility, blastomere symmetry, and survival rate when compared with eggs without inclusions.