Experiment 1
Sperm motility and duration in NaCl solutions of different concentrations are shown in (Table 1). Most of the
S.
guttatus sperm had higher motility at the range of 400-700 mM NaCl solution, the highest motility reached 91.5±2.1% when NaCl concentration was 600 mM. Duration of sperm movement increased within 250-600 mM NaCl solution, the longest duration achieved 788.0±16.9 s when NaCl concentration was 600 mM.
Experiment 2
The results of effects of different pH solution on sperm activity and duration are shown in (Table 2) Significant test for the effects of pH on the sperm activity and duration are shown in (Table 3 and Table 4). The sperm had no activity at pH 4, sperm activity was observed at pH 5, and there was a higher motility in solutions at the range of pH 5-8 (above 70%) than at other pH tested. Duration of sperm was relatively longer within pH 5-8 (above 400 sec), the longest duration recorded at pH 8 and the time was 769.0±19.8 s.
Experiment 3
Sperm activity and duration in different temperature seawater are shown in (Table 5). Significant test for the effects of temperature on the sperm activity and duration are presented in (Table 6 and Table 7). The activity and duration added at the range of 10-25°C gradually, best activity and the longest duration recorded at 25°C, subsequently, the activity and duration declined significantly with the increase of temperature, the sperm motility and duration dropped to (65.0±7.1) % and 599.5±20.5 s respectively at 40°C.
The osmotic concentration of the activator had a significant effect on the activity of sperm that became motile after dilution
(Takai and Morisawa, 1995). Obviously, lower than 250 mM NaCl solution was unable to activate sperm of
S.
guttatus, the sperm was also motionless in more than 850 mM NaCl, the sperm had better motility at the range of 500-600 mM NaCl (salinity 30-35). The optimum salinity required for sperm movement is closely related to the reproductive salinity of the species
(Jiang et al., 2000). Current research results were consistent with the salinity required (32.5-34) during reproduction of
S.
guttatus (Liu
et al., 2009).
Ohta and Izawa (1996) reported that eel spermatozoa were motionless in 300-400 mOsm/kg NaCl, but the sperm could be activated in more than 500 mOsm/kg solutions, the results didn’t agree with ours. In current study, the sperm could be activated in more than 250 mM (about 500 mOsm/kg) NaCl and the sperm had no motility in 250 mM (about 500 mOsm/kg) NaCl. One factor motivating the activity of the
S.
guttatus spermatozoa was an osmotic pressure increase, so the diluents of
S.
guttatus spermatozoa should be isotonicity.
Chambeyron and Zohar (1990) also emphasized the importance of isotonicity in the diluents for marine teleost (
Sparus aurata) spermatozoa, the motility of spermatozoa was inspired by the increase of osmotic pressure.
Generally speaking, pH has been thought as having no significant effect on the activity of fish spermatozoa. However high pH could enhance and prolong sperm activity in different freshwater and marine teleosts
(Stoss and Donaldson, 1982). The spermatozoa of
Epiniphelus coioides was more adaptable to pH and the sperm motility was the highest at pH 6.5~8.7
(Zhao et al., 2003). The eel spermatozoa had a wide range of adaptation to pH and had high vitality within the range of pH 4~11, the spermatozoa had higher motility and longer duration at pH 3 and 4, which was very unique
(Huang et al., 2011). In current study, seawater of pH 4 and pH 12 couldn’t activate
S.
guttatus spermatozoa, there was no significant difference in sperm activity at the range of pH 4-12. The results showed that
S.
guttatus spermatozoa had higher activity and longer duration at pH 5-8, which also implied that
S.
guttatus spermatozoa could adapt to a limited range of pH.
The velocity, activity and longevity of spermatozoa rely on temperature of the activating solution
(Stoss, 1983; Billard et al., 1995). Because the energetic resources of fish spermatozoa are limited, an increase in velocity caused by such a temperature rise of the living water environment leads to reduce the duration of movement
(Schlenk and Kahmann, 1938). The studies on the rainbow trout spermatozoa showed that both the motility and the movement duration declined when the temperature of the water environment increased
(Billard and Cosson, 1988). The optimum temperature of sperm motility in
E.
coioides was 25-31°C
(Zhao et al., 2003), which was a little higher than that of
S.
guttatus. The activity and duration of eel spermatozoa added with increase of temperature at the range of 18-24°C, but the activity and duration declined with addition of temperature at the range of 24-30°C
(Huang et al., 2011), the results was similar to ours. In present study, the motility and duration of
S.
guttatus spermatozoa increased at the range of 10-25°C gradually, but the activity and longevity declined markedly at the range of 25-40°C. The results indicated that temperature had great effects on the activity of
S.
guttatus spermatozoa.
