Determination of differences in the biochemical properties of sperm activating and non-activating ovarian fluids and their influences on sperm motility in rainbow trout (Oncorhynchus mykiss)

Ovarian fluid (OF) of individual female fish can initiate and affect sperm motility characteristics differently. Although it is naturally expected that OFs should stimulate and prolong sperm motility, some OFs inhibit sperm motility. In this study, 7 of 41 samples the OFs of different female Oncorhynchus mykiss inhibited sperm motility, while the other OFs initiate sperm motility and dissimilarly affect the progressive motility percentage (%), the duration of progressive motility (s) of sperm. This study aimed to figure out the differences between the activating and non-activating OFs with respect to the concentrations of the major inorganic ions (Na+, K+, Cl−, Ca2 +, Mg2 +), protein, cholesterol, glucose, osmolality, pH, catalase activities, and lipid peroxidation levels. The significant differences were found between all parameters, except Cl−, of the sperm activating and non-activating OFs (P < 0.05). The concentrations of K+, Ca2 + and Mg2 +, protein cholesterol, glucose and enzymatic activities in the non-activating OFs were higher, while their Na+ and pH levels were lower than those in the activating OFs. The non-activating effect of OFs on sperm motility is mainly due to the ionic composition, especially K+, rather than pH.