Find your recipe’s goal: salty brine (use anchovies/herring), oily richness (use mackerel/tuna), or smoky depth (use smoked salmon).
Start with the listed ratio; drain any very wet-packed fish before adding.
If your substitute tastes sharper/saltier than sardines, rinse chopped anchovies and reduce added salt in the recipe.
If it tastes flatter, add a small pinch of salt or a tiny squeeze of lemon/vinegar to mimic sardine’s bright edge.
Fold in gently at the end for sandwiches or quick sauces to keep a sardine-like bite.