Place the fish in a pot of boiling water.

Season with salt and pepper, and when the fish is cooked, remove it from the pot.

Strain the broth to remove any fish remnants, then add the potatoes and carrots.

After a few minutes, add the onions, a small bunch of celery, and the peeled tomato.

Toward the end of cooking, add the lemon juice and a little olive oil, then return the fish to the pot after removing the bones.