60ºC Some dense-fleshed fish, including tuna and salmon, are especially succulent at 120ºF, when still slightly translucent and jelly-like Creatures with a large proportion of connective-tissue collagen — notably the cartilagenous sharks and skates — benefit from higher temperatures and longer cooking to turn it into gelatin, and can be chewy unless cooked to 140ºF/60ºC or higher Some molluscs are also rich in collagen and benefit from long cooking (p 225) Why Some Fish Seem to Dry Out Faster Than Others One puzzling aspect of fish cooking is the fact that different fish can have surprisingly different tolerances for overcooking, despite similar protein and fat contents Rockfish, snappers, and mahimahi, for example, seem more moist and forgiving than tuna or swordfish, which tend to become firm and dry very quickly Japanese researchers have peered through the microscope and identified the likely culprits: the enzymes and other proteins in muscle cells that are not locked in the contracting fibrils, but float free in the cell to perform other functions These proteins generally coagulate at a higher temperature than the main contractile protein myosin So when myosin coagulates and squeezes cell fluids out, these other proteins flow out with the fluid Some of them then coagulate in the spaces between the muscle cells, where they glue the cells together and prevent them from sliding easily apart when we chew Highly active swimmers like tunas and billfish require more enzymes than sedentary bottom fish like snappers and cod, so their fibers get glued more firmly to each other if they are cooked to 130ºF/55ºC and above ... these other proteins flow out with the fluid Some of them then coagulate in the spaces between the muscle cells, where they glue the cells together and prevent them from sliding easily apart when we chew... through the microscope and identified the likely culprits: the enzymes and other proteins in muscle cells that are not locked in the contracting fibrils, but float free in the cell to perform other... other functions These proteins generally coagulate at a higher temperature than the main contractile protein myosin So when myosin coagulates and squeezes cell fluids out, these other proteins flow out with the fluid