I bought a grouper from Rivervale Mall NTUC fairprice and it was cleaned and prepared by the staff before bringing it home. During steaming of the fish, it looked fine but when we started eating it, we found a disgusting black substance flowing all about the fish body.
Eventually we found a piece of black gooey black blob which we think is coagulated grease. This is a serious health hazard if we ate the fish without checking.
I have kept the fish in my fridge in case the authorities wish to inspect the unknown black substance.