Natural Flavors

• Shallow poaching requires partial submersion in liquid, which often includes aromatics such as herbs or other fragrant vegetables, and an acid. This cooking liquid is often referred to as "cuisson." The cuisson will contribute strong and concentrated flavors, so choose a less "outgoing" fish to absorb those notes.

  One defining difference in fish flavor is fat and oil content. A fatty fish like salmon releases natural oils when cooked, making it a bold choice. Milder and lower-fat fish like halibut and trout possess naturally light and buttery flavors that complement a cuisson well.

Muscle Texture

• Though it is a low-intensity cooking method, shallow poaching might require some turning and flipping due to the incomplete submersion in cuisson, or cooking liquid. Choose a fish with a hardier texture that withstands long cooking times. As a general rule, though, move and turn the fish as little as possible to avoid flaking.

  Swordfish steaks seem like heavy and hearty options, but swordfish's high-fat content is not ideal for moist-heat cooking. Halibut and haddock -- think fish and chips -- are excellent choices for their firm flesh and low-fat content.

Fillet Thickness

• Thicker cuts of meat take longer to cook than thinner cuts, and with a method like shallow poaching, even doneness is crucial. Rounder fish like salmon naturally carry more muscle around their ribs and much less down toward the tail, resulting in uneven thickness. Flatter fish like turbot tend to distribute muscle more consistently. All parts of a fillet must be the same thickness to ensure a properly cooked and safe result. Stick a meat thermometer in the thickest part of the fillet, and look for a reading of about 145 degrees Fahrenheit.

Other Considerations

• Moist-heat cooking methods typically cook foods with a combination of liquid and steam. Use a cuisson that is flavorful and dynamic. Use a fat, aromatic herbs or vegetables, an acid and water or stock to dilute. To harness steam, cut a piece of parchment paper to the size of your pan, and cut a small hole in the center for ventilation. Place this on top of the poach to keep steam inside. If you're really concerned about fish thickness, roll each fillet around a filling or spread to make them all the same size.