You can find them in two places: Behind the lumbridge church (in the river) or in the pond that's west of the sheep.
On Runescape a crayfish will heal you 1hp once eaten, and shrimps will heal 3hp.
You can crayfish at lumbridge fishing spot near the church.
One place is behind the church in Lumbridge. You need a crayfish cage to fish them.
There is a lake where you can fish crayfish northwest of Lumbridge Castle (east of Draynor Village).
Level 1.
Erm... a lobster pot or a crayfish cage.
You can buy one at Port Sarim Fishing Shop.
Personally, I prefer the spot behind the church in Lumbridge.
blue coloration for crayfish is an abnormality and i think only 1 in 100.000 are blue. so if you find one. good for you.
you can find sinebeam trees in Daemonheim on runescape
You should be able to buy on from the fishing shop in Port Sarim, you probably wont need it - but bring around 50gp just in case.
If you like RuneScape, then you will find RuneScape a good and popular game.