Northern pike is traditional for this Scandinavian-style pickle, but you can use any firm, white fish. If it's a fish you can eat raw, like albacore or mahi mahi, you don't need to freeze the fish first. All other fish -- including pike -- you need to freeze for 48 hours before you can make this. This will kill any potential parasites in the meat; freshwater fish like pike can carry tapeworms, which you absolutely do not want, even if they are a great weight-loss strategy...
Heat 4 cups of water enough to dissolve salt. Let this brine cool to at least room temperature, preferably colder. When it is cold enough, submerge the pike pieces in the brine and refrigerate overnight. Meanwhile, bring the sugar, vinegar, the remaining cup of water and all the spices to a boil. Simmer 5 minutes, then turn off the heat and let this steep until cool.
When the pike has brined, layer it in a glass jar with the sliced lemon peel, bay leaves and red onion. Pour over the cooled pickling liquid with all the spice and seal the jars. Wait at least a day before eating, and I find it best after about a week to 10 days. Store in the fridge for up to 1 month.
Notes
Store your pickled fish in the coldest part of your fridge and it will keep for a solid month or even 6 weeks. Your nose will be your guide when it turns. Trust me.