certainly appears to be a flounder, certainly not a plaice, the only other possibility is a flounder / plaice hybrid which are more common than most people think, when flounder / plaice produce hybrids they appear to have many more charcteristics of the flounder than plaice, there is apparently only 2 ways to be certain a flounder / plaice is a hybrid 1) dna analysis and 2) disection and the counting of certain body parts (dont have a clue which parts). one of the main characteristics of a hybrid is apparently its much faster growth rate than a pure flounder, so i think a hybrid is a distinct possibility, no matter which it is its one hell of a flattie !!! well done