How can I detect a Gameobject touching another gameObject without using collider2D's?

I have fish gameObjects that have colliders2D so that I can click and move them. I added fish food with Collider2D’s but it was hard for me to click on the fish. After I disabled the fish food collider2D it was easier to click on the fish. Is there an alternative when detecting two gameObjeccts without colliders?

So far I got this. But its not working well when I tried the drag version

public class FishClicker : MonoBehaviour {

    public LayerMask whatIsFish;

    public float clickRadius = 0.1f;

    void Update() {

        if (Input.GetMouseButtonDown(0)) {
            var mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
            var hit = Physics2D.OverlapCircle(mousePos, clickRadius, whatIsFish);

            if (hit != null) {
                var fish = hit.GetComponentInParent<Fish>();

                if (fish != null) { fish.DoClickThing(); }

You can manually check the distance between 2 game objects, but that’s not very efficient.

The best way is to use layers to hide the fish food colliders from unwanted collisions.