What fish muscles are made of

Fish live in water and don’t fight gravity. Their muscles are built for short bursts of swimming, not for constant weight-bearing like a cow’s leg. As a result, the muscle fibers are short and arranged in thin, sheet-like layers called myotomes — those flaky segments you see when you pull apart cooked salmon.

Between those layers is collagen, the same connective tissue found in meat. But fish collagen is structurally different: it’s weaker, more soluble, and starts breaking down at around 40–45°C (104–113°F) — much lower than mammalian collagen, which needs sustained heat above 70°C (158°F). As Harold McGee notes in On Food and Cooking, fish proteins begin to denature at just 40°C (104°F), making fish far more sensitive to heat than chicken (which starts at 55°C) or beef (50°C). That difference explains everything.

The narrow window between raw and overdone

Fish proteins start denaturing — unfolding and firming up — around 40°C. By 60°C, the proteins have tightened enough to squeeze out moisture. At 70°C, the flesh is dry and rubbery. That’s a very narrow window, which is why fish feels unforgiving compared to chicken.

The sweet spot for salmon is an internal temperature of 50-55°C: the proteins are set, the flesh flakes cleanly, but it’s still moist. An air fryer at 200°C reaches that internal temperature in about 10 minutes for a standard 2 cm thick fillet.

Why the air fryer works well for fish

The intense circulating heat of an air fryer cooks fish quickly and evenly. Dry heat helps the surface firm up and take on color without steaming, which would make the flesh watery. The skin, if left on, also acts as a natural barrier that slows moisture loss from below.

The speed is actually a feature: because fish cooks so fast, there’s less time for the proteins to tighten and squeeze out moisture. In and out in 10 minutes means less overcooking risk than a 35-minute oven roast.

The thickness rule

Cooking time scales directly with thickness. A good rule: 10 minutes per 2 cm of thickness at 200°C in an air fryer, or 10 minutes per 2.5 cm in a conventional oven at 220°C. A standard 2.5 cm thick fillet reaches the USDA’s recommended safe internal temperature of 63°C (145°F) in approximately 10–12 minutes at 200°C (400°F) in an air fryer. If your fillet is 3 cm thick, add a few minutes. If it’s thin and tapered, check it earlier than the recipe says.

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