Study on hydration process of the rainbow trout (Oncorhynchus mykiss) oocyte during its development

In this study، the osmotic factors affecting oocyte dehydration process (sodium، potassium، calcium، chloride، inorganic phosphorus and total protein) both ovarian tissue and plasma of rainbow trout during oocyte development were investigated. Many teleost oocytes show increasing the oocyte volume and water content during the final maturation، a process known as oocyte hydration. The plasma of developing fish after blooding and also oocyte after being homogenized were kept in -20oC for analysis of parameters. The sodium and potassium ions by a Flamephotometry، chlorine، calcium and inorganic phosphate with a Colorimetry and finally total protein by the Bradford method along with the water content، osmolarity and diameter of oocyte in three developmental stages Previtellogenesis، Vitellogenesis and Maturation were measured. The results showed that potassium، sodium and chlorine with inorganic phosphorus in the oocyte had a significant trend (P<0. 05) while the oocyte protein and plasma calcium showed a significant decline (P<0. 05). In addition، the strong positive correlation between the amount of water and potassium، inorganic phosphorus، sodium and chlorine of oocyte، respectively، were present. It seems that all the mentioned changes، provide the force necessary to pull water into oocyte for hydration. In general، due to the presence of benthophil eggs in the rainbow trout، the oocyte hydration process compared to marine fish oocytes occur less nonetheless، the use of ions such as potassium، sodium and chlorine according to their important role in hydration phenomena can be studied for the more rapid maturation of ovarian trout in the artificial centers.