Identify your cook method: gentle baking/poaching (flaky) vs. high-heat browning (firmer).
Choose the closest substitute from the list: haddock or pollock for flaky, lean swaps.
Use the ratio in the table; if your substitute is thicker (like halibut), reduce quantity and shorten time.
Adjust doneness: stop when the fish flakes with a fork (or reaches opaque centers) rather than cooking by minutes alone.
Season with extra support: add salt earlier and pair mild fish with acid (lemon or vinegar) to mimic cod’s brightness.