You have to trade it while holding a Dragon scale.
Seadra evolves into Kingdra at level 45.
If you want to evolve seadra to kingdra you must level it to 38 or higher then you will be sure that when you trade it it will evolve
Seadra can be evolved at any point in the game; to evolve it into a Kingdra, you must first get a Dragon Scale and give it to him/her. Then you must trade it and voila, your Kingdra.
Seadra evolves only if you trade it while its holding a dragon scale then take it back and it will be a kingdra instead.
you have to trade a seadra while it is holding a dragon scale
well acually a horsea evoves into a seadra at 32 to get a kingdra you must trade seadra with dragonscale
train it to lvl 38 and trade it then pickaboo it will evolve into kingdra
Horsea evolves into Seadra, starting at level 32. Seadra, then, can evolve into Kingdra, while holding a Dragon Scale and traded.
If you mean Horsea evolves into Seadra its at level 32, but if Kingdra is what you are looking for you need to trade seadra while holding dragon scale.
You have to give the Seadra a Dragon Scale then trade it (and back) and it will evolve into a Kingdra.
Have your Seadra hold a Dragon Scale, then trade it with a friend. Seadra will then evolve into a Kingdra.
Horsea evolves into Seadra starting at level 32, and then Seadra evolves into Kingdra if it is traded while holding a Dragon Scale.