Biochemical and histological studies of over-ripened oocyte in the Caspian brown trout (Salmo trutta caspius) to determine biomarkers for egg quality

Abstract

The aims of the present study were to determine the best time for egg stripping after ovulation and to study oocyte over-ripening in the Caspian brown trout (Salmo trutta caspius). Eggs were retained in the female abdominal cavity for 40 days post ovulation (DPO). Partial volumes of eggs stripped from 10 individually identified females at 10 days intervals and fertilized with a pool of semen obtained from 8 males. The biochemistry and histology of the eggs and the biochemistry of the ovarian fluid were studied. The eyeing and hatching rate of the eggs declined with over-ripening time, which decreased from 90.60±6.28% for eyeing and 86.33±6.82% for hatching in newly ovulated eggs (0–10 DPO) to 1.34±0.67% for eyeing and 0.98±0.49% for hatching in over-ripened eggs (30–40 DPO). However, larval abnormalities remained constant for 30 days after ovulation. During the course of oocyte over-ripening, the pH of the ovarian fluid significantly decreased and the concentration of glucose, protein, calcium, iron, and aspartate aminotransferase activity significantly increased. Moreover, the concentration of protein, triglycerides, and aspartate aminotransferase activity in the eggs changed with over-ripening. In the newly ovulated eggs, the yolk consisted of homogenous tissue and its perivitelline space diameter had no considerable differences. With over-ripening, the yolk became heterogeneous, and while chorion diameter did not change, the perivitelline space diameter varied among different areas. The present study demonstrated that the best time to take Caspian brown trout eggs after ovulation at 7±0.6°C was up to 10 DPO. Among the studied parameters of the egg and ovarian fluid, egg quality was related to both ovarian fluid parameters (pH, protein, aspartate aminotransferase, glucose, cholesterol, triglycerides, calcium) and egg parameters (iron, aspartate aminotransferase), suggesting that these parameters can be used as egg quality biomarkers for Caspian brown trout.