Want to move 2d fish sprites in pond !

I am trying to move some 2d fish sprites in a pond.But they are not moving properly.I have attached same script to all fish objects.Can anybody tell me whats wrong with my code. Here is my code -

 bool moveFish = true;
 bool insideBounds = false;
 public float speed  =.5f;
 
 float minY = -1.1f;
 float maxY = 1f;
 float minX = -2.1f;
 float maxX = 2f;
 
 void Start () {
     Invoke("ChangeDirection",1);
 }
 
 void Update () {
 
         if(!IsInsideTheBounds()){
             if(insideBounds){
                 insideBounds = false;
                 transform.Rotate(new Vector3(0,0,-150));
                 Invoke("MakeReady",10f);
                 return;
             }
         }
 
         if(moveFish)
             transform.Translate(-Vector3.up * Time.deltaTime * speed);
 }
 
 void ChangeDirection(){
         if(IsInsideTheBounds())
         {
             Debug.Log("IsInsideTheBounds true");
             insideBounds = true;
             transform.Rotate(new Vector3(0,0,Random.Range(-20,50)));
 
         }
         Invoke("ChangeDirection",10f);
 }
 
 bool IsInsideTheBounds(){
     bool overlap = false;
     if(transform.position.x > minX &&
        transform.position.x < maxX &&
        transform.position.y > minY &&
        transform.position.y < maxY ){
        overlap = true;
     }
     return overlap;
 }
 
 void MakeReady(){
     insideBounds = true;
 }