SPERM MOTILITY ANALYSIS OF MEDAKA Oryzias latipes: OPTIMIZATION OF CASA-MOT SYSTEM AND THE EFFECT OF TEMPERATURE AND PHOTOPERIOD

Research on fish gamete has been increased in the last years, although more information about sperm characteristics is necessary to improve the assisted fertilization procedures. Spermatozoa behaviour and the effect of environmental parameters, such as temperature and photoperiod, on fish sperm quality are two important issues to be considered .  Manipulation of photoperiod and temperature are commonly used to optimize production through enhancement of growth, which could also be associated to maturation of some fish species, as Atlantic salmon. The knowledge of how photoperiod and temperature affect the maturation, and consequently the fish sperm quality, is still very limited. In  this work were evaluated the effects of temperature (low and high temperature) and photoperiod (short and long day) on the sperm quality of the model species Medaka . Twenty animals (both males and females) were kept in different tanks with the follow conditions: low temperature and short day (12ºC, 7h); low temperature and long  day (12ºC, 14h); high temperature and short day (27ºC, 7h); high temperature and long day (27ºC, 14h) (Figure 1) . After one month, sperm samples were collected from ten males and quality assessment were performed by the CASA-Mot ISAS®v1 system. The animals exposed to low temperature showed low concentration and short duration of sperm motility, whereas the fish exposed to high temperature and long day presented big testes with high sperm concentration and longer duration of sperm motility (Table 1) . However, at high temperature and short day the Medaka males presented small testis or non-existent.  In conclusion, the temperature affects the sperm concentration and motility, while the photoperiod could be more related with the maturation of the  gonads.