chapter 3 - RiuNet

GENERAL INTRODUCTION
2. Sperm physiology in fish
Fish are the most diverse and numerous group of vertebrates (Helfman et
al., 2009). However, our knowledge of fish spermatogenesis is limited to a
few species used in basic research and/or in aquaculture biotechnology
such us guppy, medaka, salmon, eel, etc. (Schulz et al., 2010).
In basic terms, spermatozoa are the result of a maturation process, called
spermatogenesis, in which several haploid cells are produced with the aim
of transmitting paternal genetic information to the next generation. During
spermatogenesis, the non-functional gametes pass through the spermiduct,
turn into mature spermatozoa, and finally they become cells specifically
designed to reach and fertilize the oocyte. Spermatogenesis involves both
morphological and physiological changes, where sex steroids such as
estrogens, androgens, and progestagens regulate the complete progression
thereof (Peñaranda et al., 2010a). The duration of this process can take
from a few weeks to several months, and is usually shorter in fish than in
mammals (Cheng and Mruk, 2013). In addition, spermatogenesis is also
influenced by several external factors such as temperature, and the
development of this process under optimum species-specific conditions
allows the production of high quality gametes. Therefore, understanding
the reproductive strategy and reproductive cycle in relation to
environmental conditions seems essential for the development of proper
protocols to control maturation and spawning in fish species.
2.1 Factors determining sperm activation
During the whole spermatogenesis process, fish spermatozoa remain in a
safe environment, surrounded by Sertoli and Leydig cells and later floating
in their own fluid, the seminal plasma. At this stage, the sperm cells are
quiescent but already prepared for accomplishing their fertilizing task
(Fauvel et al., 2010). However, sperm activation will be an essential
requirement in the pursuit of female gametes, and spermatozoa exploit
their swimming ability in order to encounter the oocyte as fast as possible
(Cosson et al., 2008a).
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