Fish, you could use that same prawn brine and have a red herring that works better than it's namesake. Actually, most herring brines are intended to toughen them and add a little flash to the scales. For that reason most herring brines are based on rock salt. Use about a cup of rock salt to a small half pale of cold water and stir to disolve it well. Leave the herring in for a few hours - some leave it there all night before fishing. This also adds some sodium scent that fish like. You can also add coloring, such as blue food dye or the red Pro-Glo coloring mentioned, to try on some of the herring - not all of them in case they don't work as well on a given day. Some also put in bait oils such as sardine oil. For a trick, try a adding a few tablespoons of vanilla extract to the brine - and let us know how you do on those.