You may have seen the regulation that, for fish with a minimum, or slot, length size rule:

You must not alter the length of a fish which is subject to a minimum or maximum size limit ….You cannot remove the head or tail … This means you cannot fillet your fish or possess filleted fish if you are in, on or adjacent to the water.

There’s a news report here that tells the sorry tale of two guys who had cut a Murray Cod into steaks but were then inspected by a Fisheries Compliance Officer. Since the length of the fish could not be verified, they were fined.

https://au.news.yahoo.com/aussie-man-fined-300-for-eating-his-campsite-catch-ridiculous-072658546.html