Grate and cook the zucchini on low heat in a casserole for 10 minutes. Take away from the stow and let cool down.
Drain the water away from the mackerel fillets but keep the liquid for later.
Ina bowl mix all the ingredients except the carroty. Use an electrical blender for this.
Heat up the oven at 180 degrees Celsius.
Peel and slice the carrot in thin slices.
Butter a rectangular baking form. Add half of the fish mixture.
Place the carrot on top of the mixture.
Add the rest of the fish mixture.
Place the terrine in the middle of the oven for 40 minutes. Take out and let cool down. Keep cold until the next day.