The study was designed to test the hypothesis that male aging is associated with a change in reproductive function in the zebrafish. Young (290 ± 37 d) and older (911 ± 48 d) males were combined with females (604 ± 24 d) to test the effect of male age on the number and fertility of eggs laid by their mates. 48% of breeding trials with young males and 25% of the trails with older males resulted in egg deposition. Although young males were associated with significantly more successful breeding attempts than older males, number of eggs laid per clutch, number and percent of fertilized eggs and the number and percent living embryos were not statistically different between young and older males. These data suggest that male aging is associated with altered reproductive behavior and/or female response but not in sperm quality per se. Consistent with this interpretation were the findings that percent motility and sperm motility characteristics did not differ between sperm from young and older males as assessed by computer-assisted sperm analysis. However, older males contained higher quantities of extractable sperm than did young males, perhaps associated with fewer successful breeding attempts. Age-related effects on male reproductive in the zebrafish may therefore be a consequence of behavioral or morphological features that play a role in female mate choice and/ or male sexual response.
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