[Zbrafish] could anyone help?to collect the definitive develomental stage embryo

[x-man]

           collect the definitive develomental stage embryos feaze me
grievous,especially the 36hpf embryos,and the "head-trunk angle"
methode refered by the zebrafish book is not very useful because i
found that there is no obvious different between 36hpf and 37hpf
embryo,so do you have any better way and could you give me any
advice?thanks very much~