Cut the celery into diamonds, finely chop the greens and set aside for decoration. Peel pieces of the zucchini with a ball cutter or dice with a knife.
Heat the olive oil in a saucepan. Sweat the celery lozenges and the zucchini pieces in it and cook over low heat. Season with pepper and salt.
Stew the tomatoes in a little olive oil with the saucepan closed and low heat for about 15-20 minutes. Salt a little. The liquid from tomato juice and olive oil can be whipped with a whisk and seasoned to taste to make a lean sauce for the dish.
Cut the loach fillet into portions, dust the skin side a little with flour and fry well in a mixture of butter and olive oil. The flour browns and protects the meat so that it doesn`t burn.
After 2 minutes, turn the heat down to half. After a total of approx. 4 minutes, turn the fillets and finish cooking in approx. 5 minutes with the plate open.
Arrange the vegetables and fish together on plates and decorate with the finely chopped celery greens and trout caviar. This goes well with mashed potatoes.