Simple 2D Fish Obstacle Avoidance

I am currently working on a simple obstacle avoidance system in unity. I have a player and a school of Ai fish that are traveling in a fixed direction (Down-Right). While swimming, I want the Ai fish to keep away from the player, and also keep away from incoming obstacles. I first thought I should use a boid flocking algorithm, but it may be overkill for what I need as I am trying to limit computation to as low as possible since it will need to run on a mobile device. the fish do not need to avoid each other and they simply need to head toward the fixed direction. Other notes: I can't use unity's NavMesh system since I am using 2d physics and obstacles will be random at runtime.

My issue is that I do not know how to efficiently steer the AI when there are multiple obstacles and players in the proximity. I have something working(Below), but I am manually steering it when it gets too close but this won't work when I have multiple obstacles to avoid within their proximity. Could someone steer (ha) me in the right direction on how to approach this?

Thank You

Below is the class I made for the Ai fish:

public class FishMoveTest : MonoBehaviour {
public float Speed;
Rigidbody2D rb;
public float MinSpeed;
public float MaxSpeed;
public float DisableDistance;
private float DistanceFromPlayer;
public GameObject Player;
 Material NormalMat;
public Material CollideMat;
 MeshRenderer MeshRend;
public UnderwaterObstacle _UnderwaterObstacle;
public float AvoidDistance;
public float SteerSpeed;
float DistanceFromObstacle;
// Use this for initialization
void Awake () {
    MeshRend =  GetComponent<MeshRenderer> ();
    NormalMat = MeshRend.material;
    rb = GetComponent<Rigidbody2D> ();
    Speed = Random.Range (MinSpeed, MaxSpeed);
}

// Update is called once per frame
void FixedUpdate () {
    DistanceFromObstacle = Vector3.Distance(transform.position, _UnderwaterObstacle.Obstacle.position);
    if (DistanceFromObstacle < AvoidDistance) {
        CastObstacleRay ();
        if (MeshRend.material != CollideMat) {
            MeshRend.material = CollideMat;
        }
        if (transform.position.y > _UnderwaterObstacle.Obstacle.position.y) {
            //Move Up-Right;
            rb.velocity = Vector3.Lerp(rb.velocity,new Vector3 (0.5f, 0.5f, 0) * Speed,SteerSpeed);

        } else {
            //Move Down
            rb.velocity = Vector3.Lerp(rb.velocity,new Vector3 (0, -1, 0) * Speed,SteerSpeed);
        }
    } else {

        rb.velocity = Vector3.Lerp(rb.velocity,new Vector3 (0.5f, -0.5f, 0) * Speed,SteerSpeed);
        if (MeshRend.material != NormalMat) {
            MeshRend.material = NormalMat;
        }
    }
}