Accelerated whitening of rainbow trout (Oncorhynchus mykiss) unfertilized eggs under the effect of saline solutions for their mechanical sorting

The whitening of unfertilized salmonid eggs during artificial incubation allows their elimination by mechanical sorting. This phenomenon that normally appears throughout the incubation period in rainbow trout could be accelerated by exposing shortly the eggs to marine salt solutions. The effects of various combinations of salt concentration and exposure time on further eggs whitening and embryos abnormalities rates were assayed at various developmental stages of rainbow trout eggs (140, 190 and 240 degree*days). The transfer during 1 to 20 min in a saline solution between 30 to 120 g/l salinity increased significantly the whitening of unfertilized eggs without affecting that of fertilized ones. All treatments promoted a significant increase of embryonic mortality at 140 degree*days and of larval abnormalities at 190 degree*days, probably through a mechanical handling effect. At 240 degree*days, handling did not affect the embryonic development but led to a hatching delay of a few hours. This study offers new prospects to improve mechanical sorting of unfertilized and fertilized rainbow trout eggs during incubation.