Your Ahi Tuna Isn't Searing Properly, And Here's The Likely Problem - Tasting Table

"Overcooking is one of the biggest mistakes you can make when searing ahi tuna, and it may cost you the integrity of the entire steak. Despite its buttery taste, the fish has a low fat content that prevents it from retaining moisture when it encounters excessive heat. Cooking it quickly ensures that you end up with a center that's perfectly tender and flaky."

"There's nothing like hearing the sizzle and pop of tender fish searing in a pan, but don't let the joy of that experience make you prolong it more than necessary. Ahi tuna also has fragile connective tissue, so it doesn't take much heat to turn the once-delicate flesh rubbery. As you cook the fish, the proteins lose their structure and bind together to create a new form. When met with excess heat, these proteins will tighten up even further, resulting in an overly firm texture."

Ahi tuna benefits from very short, high-heat searing to develop a caramelized exterior while keeping the interior tender and flaky. The fish's low fat content reduces its ability to retain moisture under prolonged heat, and fragile connective tissue and proteins tighten when overcooked, producing a rubbery, overly firm texture. Browning for roughly one to two minutes per side is a useful guideline, with total cooking time adjusted for steak size and desired doneness. Medium-high to high heat is recommended to form crisp edges without prolonged exposure to excessive heat.

Read at Tasting Table