The food in question here is Swai Fillets (Vietnamese catfish). When I look up the nutrition info for it I see most places list it around 70 calories for 4 oz. with a very few going up into the 90s. However. the particular brand I have (Great American Seafood) says 170 as do a few other brands. How is this possible?

Depends on whether it was wild or farm raised, what it ate, etc. Always go by the manufacturer's nutritional information. 70 calories for 4 oz. sounds very low for catfish.

Is the difference possibly raw versus cooked weight? Most animal proteins lose moisture and therefore weight during cooking, so it may take 6 ounces of raw fish to make 4 ounces of cooked fish.

Quilter - I was definitely planning to use the info for the brand I have, I was just really curious about such a big difference.

Kaplods - That sounds like a logical explanation. If that is what they did though I wish they would have marked it as such. Now I'm not sure if I should weigh my fish before or after cooking. I may do both and take the halfway point.

If the label doesn't say "cooked weight" then it should be the weight of the fish in the package (I would think before thawing - which should be about the same after thawing unless the fish are deliberately coated in a layer of ice).

You may also check the label for an ingredient list. It's not uncommon for meats to be injected with or soaked with a marinade or brine solution of salt and sugar, and sometimes even added fat, but if so there should be an ingredient label somewhere on the package.