random movement like fish

[Biohazzrd]

for school we are making a fish tank in flash where we each make a fish and I have been entrusted with duty to program the random movement like fish do i have some code but it doesent work. Here it is:

code:

Object.prototype.move = function  () {         rotAdd = (random(100-(vita*rot))-50)/100;         rot += rotAdd;         _rotation  += rot;         posX = this.tempo * Math.sin((_rotation/180)*Math.PI);         posY = -this.tempo * Math.cos((_rotation/180)*Math.PI);         _x += posX;         _y += posY;         if ((((_x < -20) or (_x > 550)) or (_y < -20)) or (_y > 500)) {             _rotation += 180;         } };

This is supposed to go into the first frame of the root time line and the this bit of code goes to themovie clip on the root timeline:

code:

onClipEvent(enterFrame){ move; }

this is supposed to be what it looks like, go to this link (http://friendsofed.infopop.net/2/OpenTopic?a=tpc&s=989094322&f=3953051263&m=6483039495)
and go to the "fish V1" in examples in the first post