Fish Sperm Physiology: Structure, Factors Regulating Motility, and Motility Evaluation

Abstract

For reproduction, most fish species adopt external fertilization: their spermatozoa are delivered in the external milieu (marine-or freshwater) that represents both a drastic environment and a source of signals that control the motility function. This chapter is an updated overview of the signaling pathways going from external signals such as osmolarity and ionic concentration and their membrane reception to their transduction through the membrane and their final reception at the flagellar axoneme level. Additional factors such as energy management will be addressed as they constitute a limiting factor of the motility period of fish spermatozoa. Modern technologies used nowadays for quantitative description of fish sperm flagella in movement will be briefly described as they are more and more needed for prediction of the quality of sperm used for artificial propagation of many fish species used in aquaculture. The chapter will present some applications of these technologies and the information to which they allow access in some aquaculture species.Biological Research in Aquatic Science 2 the current knowledge with respect to (1) membrane reception of the activation signal and its transduction through the spermatozoon plasma membrane via the external membrane components such as ion channels or aquaporins; (2) cytoplasmic trafficking of the activation signal; (3) final steps of the signaling, including signal transduction to the axonemal machinery, and activation of axonemal dynein motors and regulation of their activity; (4) signaling involved in guidance processes that control the sperm/egg approach and meeting; and (5) pathways supplying energy for the short flagellar motility period of fish spermatozoa. For each step in this signaling process, quantitative methods were developed to evaluate the quality of the sperm samples that are used for aquaculture propagation of many fish species. These methods as well as examples of their usefulness for application to fish artificial reproduction are presented in the last part of this chapter. Fish sperm structure and spermatogenesisThe main traits of the flagellar mechanics of spermatozoa and the main factors that regulate their motility have been described in details in a recent review chapter by Cosson et al. [1]. Structure of fish spermatozoa: a brief presentationCompared to mammalian spermatozoa, the structure of a fish spermatozoon is qualified as "simple sperm", mostly because the flagellum structure does not include additional columns flanking the motor part (axoneme) that are present in mammal sperm. In teleost fish, spermatozoa generally have no acrosome (in contrast to chondrostean such as sturgeon), and the impenetrable chorion presents a micropyle that gives access to the membrane of the oocyte. Spermatozoa often show a spherical nucleus with homogenous, highly condensed chromatin, a nuclear fossa, a midpiece of variable size with or without a cytoplasmic channel, and one or two long flagella [2]. Moreover, fish spermatozoa can be classified into two forms, a...

Ovarian fluid proteome variation associates with sperm swimming speed in an externally fertilizing fish

“…In mammals, Ca 2+ ‐independent flagellar dynein and ATP orchestrate the low‐amplitude sinusoidal‐activated motility of the tail, but hyperactivated motility requires Ca 2+ to enter the sperm through specific channels, such as Catsper, as part of the capacitation process (Qi et al., 2007). Activation of sperm motility in teleost fish also requires Ca 2+ influx (Cosson, 2019), but because teleost fish lack Catsper channels, Ca 2+ signalling must involve a different process to those of marine invertebrates and mammals (Fechner et al., 2015). In fish, sperm flagella are able to respond to regulation by free calcium concentration by altering their beating pattern (Cosson, 2019).…”

“…Activation of sperm motility in teleost fish also requires Ca 2+ influx (Cosson, 2019), but because teleost fish lack Catsper channels, Ca 2+ signalling must involve a different process to those of marine invertebrates and mammals (Fechner et al., 2015). In fish, sperm flagella are able to respond to regulation by free calcium concentration by altering their beating pattern (Cosson, 2019). However, another potential mechanism may lie in the regulation of the focal adhesion complex, that both alpha actinin and filamin contribute to, which is important for capacitation and thus hyperactivation of mammalian sperm (Roa‐Espitia et al., 2016).…”

Effects of anesthetic tricaine on stress and reproductive aspects of South American silver catfish (Rhamdia quelen) male

“…In addition to cortisol, anesthetics may also interfere with this parameter, since direct contact between MS-222 and sperm decreased the sperm motility time of O. mykiss [28]. In the present study, sperm motility presented a negative linear response, suggesting that stress-related hormones have induced osmoregulatory dysfunctions [38] causing blood plasma dilution and alteration in seminal plasma osmolarity [37], causing pre-activation of spermatozoa and, consequently, decreased sperm motility [35].…”

Sperm vitrification of Prochilodus brevis using Powder Coconut Water (ACP‐104) in association with different cryoprotectant concentrations

“…However, few normal cells were observed after vitrification (only when ACP-104 was used), with normal free head and strongly coiled tail being the most common abnormalities. An increase in sperm pathology can reduce cell motility (Cosson, Billard, Cibert, Dréanno, & Suquet, 1999), which may explain that the highest motility rates observed were 22.73 ± 0.73% and 27.94 ± 1.01%, when 5%…”