Energetics of fish spermatozoa: The proven and the possible

- Elucidation of interrelationship between the sperm bioenergetics processes and flagellum mechanical motion is still needed.
- In this chapter, previously reviewed knowledge and recent data in the field are upgraded.
- Recent studies on applied aspects of fish sperm bioenergetics are summarized.

Main features specific to sperm of fish with external fertilization are 1-the seminal fluid osmolality, and in several species, some ions prevent sperm motility in the genital track; 2-transfer from seminal fluid into sea- or freshwater triggers full motility due to osmotic and/or ionic signal; 3-immediately after activation, fish sperm swim with very high efficiency; 4-the motility period is limited to a very short duration for freshwater sperm and not for much longer in case of marine fish spermatozoa; 5-most motility parameters are decreasing and wave shape is changing during the motility period; 6-the regulation of axonemal motility by ionic concentration, as well as by ATP concentration and other substances, can be observed in vitro by using membrane-deprived spermatozoa; 7-the chemical energy available in fish spermatozoa is rapidly exhausted during the swimming period; 8-the membrane potential of the spermatozoon represents an important aspect of the cell electro-chemical energy homeostasis; 9-the ultimate task for sperm, before fertilization, is to meet an egg, and this task is facilitated by chemotaxis.The present chapter will tentatively deal with some of these salient features such as a-osmolality and ionic signals controlling fast but short-lasting motility in connection with ATP and other energetic compounds management; b-role of sperm electro-chemical potential in the trans-membrane management of this complementary aspect of sperm energetics; c-considerations on physical energy needed by moving fish flagella; and finally, d-how oriented motility governs sperm behavior while swimming toward egg. Finally, recent studies on applied aspects of fish sperm bioenergetics are summarized.