Frozen Tilapia from the box stores are typically farmed from China or Taiwan. All packaged fillets contain Carbon Monoxide (color retention), bag will state where the fish was farmed (country), and production date (freshness).
As for the fresh version from Costco. Is it farmed in the U.S.? I've seen them before and price is high. So, I never read the label. Was it previously frozen and treated with CO2 (Carbon Monoxide) ? Are the consumers paying for the service of thawing and repacking? Just something to think about that's all.
I've personally used fz tilapia fillets from box stores such as Winco, Cash & Carry, Walmart, Safeway, Fred Meyers. All similar in my opinion in texture and smell. The color retention for me is visually the difference.