He can tell grouper from tilapia.

But would Nova Southeastern professor Mahmood Shivji's DNA abilities be enough to settle that most perplexing of seafood mysteries, the McDonald's Filet-O-Fish sandwich?

Filet-O-What, exactly?

The Miami Herald was determined to find out. Doing so required a trip to the local McDonald's drive-thru.

After scraping the breading, cheese and tartar sauce from two Filet-O-Fish sandwiches, the square patties were frozen inside Ziploc sandwich bags.

Then it was off to the lab, where Shivji graciously agreed to waive his normal $192-per-sample processing fee.

Shivji and his team peeled off a tiny sliver of frozen fish and inserted it into a test tube. Through a series of chemical reactions, the DNA was extracted and subsequently amplified and sequenced. Once the species DNA profile was identified, the scientists compared it against known species until they hit a match.

``Alaska pollock,'' Shivji said at last, officially laying to rest any conspiracy theories that the chewy, mild-tasting fish patty isn't really fish at all.

``It's a fish,'' Shivji said with a laugh. ``There's no traces of pigs or anything like that.''

The authenticity of the cheese, however, could not be verified.

Pollock, a whitefish found in other fast-foot restaurants as well as frozen TV dinners, isn't exactly the Rolls Royce of seafood -- it's a key ingredient in imitation crabmeat, and folks in Great Britain sometimes feed pollock to their cats.

But, really, how much can one expect from the Filet-O-Fishat the wallet-friendly price of $2.79?

While pollock might not be fancy, its DNA footprint in the Filet-O-Fish is proof that McDonald's -- unlike many South Florida restaurants -- is at least honest about what it serves its customers. McDonald's corporate website identifies pollock as one of two fish sources for its decades-old fish sandwich (the other being hoki, a fish found off the coasts of New Zealand and Australia).

Both fish species are recognized as sustainable, well-managed fisheries -- meaning Filet-O-Fish lovers can feel good that their guilty pleasure won't harm Mother Nature's marine ecosytems.

``Sustainable fishing floats our boat,'' the Filet-O-Fish sandwich box states.

(For those who dare look, that same box lists the sandwich's nutritional content on its bottom.)

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