Spermatogenesis and spermatology of some teleost fish species (1)
Résumé
In teleost fish, the whole of the processes involved in the formation of spermatozoa and their release and in fecundation are extremely diverse. Two main types of testicular structure are distinguished : a tubular and a lobular. Theorganization of the lobules and genital duct structure is very diverse in the latter type. Spermatogenesis can be continuous, as in guppy, discontinuous with overlapping cycles, as in carp, or show well separated cycles as in trout. Spermiogenesis shows increasing degrees of complexity, leading to the formation of extremely simple spermatozoa as in carp (spherical head, very little nuclear histone transformation, very simple mid-piece with untransformed cytoplasmic and mitochondrialremains) or much more complex spermatozoa as those of guppy (elongated head, histoneprotamine transformation, transformation of the centriolar complex in the deep nuclear notch, very developed mid-piece with glycogen stores). Spermatogenetic production is extremely variable (GSI : 0.1-10 % ; annual production : 1 $ .10 to 7 9.10 spermatozoa/g body weight). Spermiation yield varies according to species but also within the same species (20-90 % in trout). The endocrine model of spermatogenesis and spermiation is very different in carp and trout. The main environmental factor influencing spermatogenesis is photoperiod in trout and temperature in carp ; spermiation depends on temperature in trout and on social environment as well as temperature in carp. Sperm physiology (survival time in vivo and in vitro, motility time, metabolism) is very different in the several species studied. Two groups with a fundamentally different physiology (internal or external fecundation), sperm biology and morphology (structure of testis and spermatozoon) can be grossly distinguished. These groups are fish with lobular testes (guppy) and those with tubular testes (teleosts).
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