Bioenergetic pathways during non-activation, post-activation, and reactivation of motility exhausted sterlet (Acipenser ruthenus) spermatozoa

This study studied the possibility of sperm reactivation employing second motility activation, adenosine triphosphate (ATP) reloading, and regaining the fertilizing ability and the possibility of improvement in the fertilisation rate of reactivated sperm by supplementation with metabolites. The most crucial bioenergetic pathways during quiescent, motile, and reactivated states of sterlet (Acipenser ruthenus) spermatozoa were determined. Results showed that out of the studied pathways (glycolysis, mitochondrial respiration, and phosphocreatine-creatine – PCr-Cr shuttle system), PCr-Cr shuttle system was the most requested during the quiescent state. While after motility activation, no studied pathway had a significant energy supply contribution. Thus, the bioenergetic strategy to sustain sperm motility in sturgeon is similar to that in teleostean fishes. After termination of the first round of motility, the spermatozoa of sterlet were able to become motile and fertilise the egg cells after 1-h incubation in a reactivation medium. Mitochondrial respiration and the PCr-Cr shuttle system were shown to be active during the reactivation state. However, unlike spermatozoa of teleostean fishes, the sterlet reactivated spermatozoa did not demonstrate ATP reloading. This may indicate for the first time that the bioenergetic strategy during second motility activation in sturgeon sperm is divergent from cyprinids and salmonids. The fact that only part of spermatozoa can be reactivated is probably related to the existence of sperm subpopulations of specific intrinsic physiological properties. Further study of these properties will enhance our fundamental knowledge in fish spermatology and help increase the effectiveness of artificial fish reproduction.