Is ahi tuna supposed to be very sour?!

Is ahi tuna supposed to be very sour?

I bought some fresh wild ahi tuna of Fiji from Costco, but I found the fish very sour, or rather acidic after it was cooked. It doesn't appear to be treated with lemon or lime juice, according to the label. Is ahi tuna supposed to be sour, or could it be spoiled, or some other reason? Thanks.

No. I fish for tuna. I have caught and eaten blue fin, yellowfin and albacore tuna, cooked and raw, when it was only minutes or hours from being caught and I can definitely tell you that fresh ahi or yellow fin tuna has a mild taste. Not fishy or sour. It should almost taste like beef when cooked right. Tuna from Costco is almost certainly frozen and thawed for sale. Fresh tuna flown in from Fuji does not find its way to Costco but to the sushi bars and sold to those who are williing to pay the price. Your tuna probably spoiled. Did it smell fishy? Was your tuna turning brown? It should be reddish and the meat should not be separating or splitting. Also eat fish the same day you buy it.

Sorry to hear about your meal. Go to a reputable fish market and buy tuna. Make sure its say "fresh" and its does not say "previously frozen" Fresh tuna is not cheap but its worth the price.