Spawning ecology of the anchovy Engraulis japonicus in the spawning ground of the Southern Shandong PeninsulaⅡ. Spawning habits and embryonic developmental characteristics of the anchovy

The investigations on the spawning ground of the Southern Shandong Peninsula by water mass drift experiments were carried out from May to July during 2000–2004. Spawning habits and embryonic development characteristics of anchovy are studied from these observations. It is shown that duration for the germ cells fully developed from spawning to hatch are different under different temperature. The durations are 42–44 hours when the water temperature is 21.78℃–22.68℃ （averaged 22.05℃）and 50–52 hours while the water temperature is 17.05℃–18.88℃ （averaged 17.90℃）at the surface layer. In the upper mixed layer, the durations for fully development are 44–46 hours and 50–54 hours under the water temperature of 21.26℃–22.05℃ （averaged 21.70℃） and 17.02℃–17.90℃ （averaged 17.50℃） respectively. While in the thermocline, the water temperature are 16.22℃–21.26℃ （averaged 18.70℃）and 14.42℃–17.02℃ （averaged 15.72℃）, the durations are 46–48 hours and 68–72 hours respectively. One-way ANOVA showed that the anchovy embryonic development duration observed from in situ data was not significantly different from that calculated academic (P > 0.05), which indicates that both the in situ observation and academic estimation methods applied in the present study are reliable. Water temperature in the spawning ground in late June of 2003 is 1.80℃–3.80℃ lower than that of 2002. It makes the duration of anchovy embryonic development 8–24 hours longer. Developmental threshold temperature of anchovy germ cells is 10.26℃ and the sum of effective temperature is 423.1 h·℃. At the spawning season, adult anchovy produce new eggs from 19：00 in the evening till next 5：00 in the early morning. The spawning duration will last 10 hours. At night time from 21：00 to next 2：00 am is the peak spawn time. The adult anchovy mainly spawn in the thermocline [Acta Zoologica Sinica 54（6）：988–997, 2008].