For a US Southern, Louisiana twist, catfish, occasionally a bit muddy flavored, has been traditionally marinated in a mixture of buttermilk and yellow mustard, before breading and frying. Buttermilk also works well with venison to reduce the sometimes "gamy" flavor of deer shot in warm weather.

In either case, yoghurt makesa fine substitute.

I'm amused by "Australian" yoghurt. My local supermercado ain't long on plain (unsweetened/unfruited) varieties, but stocks from organic to "Greek Style" - pretty much covers memories of Turkish - and a new "Indian" sort. I don't recall any claim that Australian cows are any more natural - ... is "natural"? "Organic"? - the most over-used and PC of terms - than cows of other nationalities.