Physiological and biochemical parameters for egg quality determination in lake trout, Salmo trutta lacustris

Abstract

The present study investigated the relationships between egg viability and ovarian fluid composition, egg physiology and egg metabolism in lake trout, Salmo trutta lacustris, to obtain biomarkers for egg quality determination. The ovarian fluid pH, protein levels and activities of aspartate aminotransferase and β-D-glucuronidase were significantly correlated with egg viability expressed as the number of eyed stage embryos. Regression models demonstrated that an ovarian fluid pH between 8.44 and 8.57, protein levels below 235.56 mg 100 ml-1 ovarian fluid, aspartate aminotransferase activity below 31.65 μm min-1 ovarian fluid and β-D-glucuronidase activity below 8.62 μm min-1 l-1 ovarian fluid characterized egg batches with high viability (≥80%). The increase in the egg wet weight during water hardening was also significantly correlated with the number of eyed stage embryos, and egg batches with high egg viability (≥80%) increased in wet weight by ≥13% during water hardening. From the investigated metabolic parameters the number of eyed stage embryos was significantly correlated with activities of NADP-dependent isocitrate dehydrogenase (egg viability ≥80% at ≥2.07 nM min-1 mg-1 protein) and NAD-dependent malate dehydrogenase (egg viability ≥80% at ≥47.25 nM min-1 mg-1 protein), with the respiration rate (egg viability ≥80% at ≥8.71 nM min-1 mg-1 protein), with the ratio of NADH to NAD levels (egg viability ≥80% ≥ 0.872), with the levels of free, non-esterified fatty acids (egg viability ≥80% ≥72.34 μg mg-1 protein), and the ratio of non esterified to esterified fatty acids (egg viability ≥80% at ≥0.749). Also, subjective and visual control methods were described to distinguish between batches with viable and non viable eggs.