Energetics of Fish Spermatozoa

Abstract

Fish spermatozoa need to perceive a signal from the external milieu so as to activate their motility. The osmolarity and/or ionic composition of the marine or freshwater surrounding fish control the activation of fish sperm flagella at spawning. Flagella motility is energy dependent and the amount of energy stored in the spermatozoon prior to its activation is a main factor that will sustain their vigorous motility but for only a short period (one to several minutes) in fish until partial exhaustion of this energy stops motility. Storage of energy mostly results from mitochondrial respiration that generates ATP. Energy metabolism also involves other compounds such as creatine–phosphate that contribute to the maintenance of the intracellular energy level in connection with ATP. In few species, especially internally fertilizing ones, part of the energy comes from glycolysis. For efficient motility of swimming fish spermatozoa, the ATP usage (chemical hydrolysis) is mainly balanced by the physical power developed by the flagellum against viscosity forces: this balance sheet is also discussed in this chapter. The rest of ATP consumption is needed by fish spermatozoa for “house-keeping” tasks such as maintaining the ionic balance across the cell membrane as example.

The cryopreservation process induces deleterious perturbations at several levels of the energy metabolic network such as damage to mitochondria, leaking of cell membrane, and damage to the flagella motility apparatus that altogether lead to a serious decrease in the percentage of motile cells and consequently the fertilizing ability.