Rainbow trout egg quality determination by the relative weight increase during hardening: a practical standardization

Abstract

The relative weight of fish eggs increases during water hardening; this increase is significantly correlated with egg viability in rainbow trout when determined after 120 min, providing an assay test for egg quality control. In the present paper, additional investigations on egg water uptake at different time intervals during the hardening process were performed to correlate these with egg viability and to improve the sensitivity of the assay while also reducing the handling time. Eggs of high quality had a significantly higher rate of water uptake than low quality eggs, with the highest rate occurring during the first 30 min of hardening. Bivariate correlation coefficients and regression models revealed that in addition to egg weight increase after 120 min of water hardening, the increases in weight after 30 min and 60 min were also significantly related to egg viability (P < 0.001). In contrast, the initial weight increase after 15 min of hardening revealed a lower correlation (P < 0.006) with egg viability. These results indicate the initial velocity of water uptake is not a valid criterion, but that the total amount of water imbibed during hardening provides the most reliable information on egg quality. The present study confirms the previously reported sensitivity of the assay, and also shows that a shorter incubation time of 30 min is adequate for reliable results. The shorter handling time is an improvement for testing large numbers of egg batches.