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Changes of sperm morphology, volume, density and motility and seminal plasma composition in Barbus barbus (Teleostei: Cyprinidae) during the reproductive season

Abstract - Eighteen spermiating males were randomly selected from a hatchery-reared stock and electronically tagged to record changes in their sperm quality parameters (spermatozoa morphology, ultrastructure and motility, ionic composition and osmolality of the seminal plasma, and sperm volume and density) during the spawning season. Stripping was performed at the beginning of March, April and May. The Barbus barbus spermatozoon has a head without acrosome, a midpiece with 4-6 mitochondria and proximal and distal centrioles, and a flagellum with the typical 9+2 pairs of microtubules. Apart from posterior width of the midpiece, morphological and ultrastructural parameters changed significantly during the reproductive season; generally by decreasing toward the end of reproductive season. Sperm volume also decreased from 0.42 in March to 0.15 ml in May, and density from 18.81 in March to 12.45 10⁹ spz ml^-1 in May. Osmolality (mOsmol kg^-1) was 268 4, 276 2 and 268 2 in March, April and May respectively. Chloride, sodium, calcium and potassium ion concentrations (mM) did not show significant differences between March and April (Cl^-: 125.3 vs. 120.5, Na⁺: 75.7 vs. 69.7, Ca²⁺: 0.4 vs. 0.3 and K⁺: 84.7 vs. 84.0). The percentage of motile spermatozoa at 15 s post activation did not show a significant difference between dates, but the highest spermatozoa velocity at 15 s post activation was observed in April (91.4 3.2 m s^-1) and then decreased significantly towards the end of the reproductive season (80.6 1.9 m s^-1 in May). However, lowest spermatozoa velocity was measured in March (70.4 1.9 m s^-1). This study supports the hypothesis that longer spermatozoa swim faster. Within one stripping, velocity and percentage motility decreased significantly with time post activation. In conclusion, changes observed in B. barbus sperm parameters during the reproductive season, suggest there is association between such changes and spermatozoa aging processes.