Induction of metamorphosis of differentdayold bay scallop Argopecten irradians by chemical cues

Abstrcat The larval Argopecten irradians individuals were sampled regularly after the eggs were fertilized for 10 d and exposed to solutions of KCl (concentration gradients 13.42, 20.13, 26.85 mmol/L), epinephrine (EPI, 0.01, 0.05, 0.1 mmol/L), norepinephrine ( NE,the same as EPI), L-DOPA (the same as EPI), 5-HT (1.0,10.0, 100.0 μg/L) GABA (the same as 5-HT), theophylline (0.1, 1.0 mmol/L) and caffeine(the same as theophylline), respectively, for 8 h. After 14 d, the larvae were fixed by I2 solution and inspected . The 8 chemical cues have different effects on the larval metamorphosis at different age of days that KCl at 13.42 and 20.13 mmol/L can inhibit the metamorphosis of 12dayold larvae, but significantly increase the metamorphosis of 13and 14dayold larvae with the metamorphosis increment rate 20%, and the inductive effect reduces on day 16. KCl at 26. 85 mmol/L has inhibitive effect on 12 and 13dayold larvae's metamorphosis but can promote the metamorphosis of 14 and 16 dayold larvae with the metamorphosis increment rates of 22.98% and 37.5%, respectively. The inductive effects of neurotransmitters EPI, NE, LDOPA, 5HT and GABA are similar that they all inhibit the larval metamorphosis on day 13 but increase the larval metamorphosis on day 14. The inductive effects of theophylline and caffeine , which influence intracellular CAMP concentration, are different from neurotransmitters that the optimum inductive effects are obtained on day 13.