You asked, Diane Morgan has answered! Here's what the author of Salmon: Everything You Need to Know has to say about your fishiest questions.

I’ve heard a lot of conflicting things about eating seafood while pregnant.

Eating sustainable seafood during pregnancy can be a terrific source of protein, vitamins, and minerals, vital for a baby’s growth and development. The 2015-2020 Federal Dietary Guidelines for Americans recommend that pregnant women eat at least 8 ounces and up to 12 ounces of seafood a week, choosing seafood that is low in mercury. This recommendation is also supported by the Mayo Clinic and the American Pregnancy Association.

  • ENJOY a variety of fish and seafood that is low in mercury and high in omega-3 fatty acids, such as: wild-caught salmon, trout, steelhead, Atlantic and Pacific mackerel, anchovies, sardines, and herring. Other safe choices include: domestic, wild-caught or responsibly-farmed shrimp, Pacific cod, Alaskan halibut, rockfish, scallops, domestic catfish, tilapia, Pacific flounder, and sole. (When purchasing seafood, follow the guidelines in the Monterey Bay Aquarium Seafood Watch Guide. Available online or as an app to download.)
  • AVOID these fish that are high in mercury: shark, swordfish, king mackerel, and tilefish. As well as uncooked fish and shellfish such as: oysters, sushi, and sashimi.
  • LIMIT canned white (albacore) and tuna steaks to 6 ounces a week. Canned, chunk light tuna has lower amounts of mercury than other tuna.

What is the lowest mercury and most sustainable type of canned tuna to purchase?
In a supermarket the most commonly stocked canned tuna is either chunk light (typically skipjack) or chunk white (albacore). Canned light tuna typically contains 0.12 parts per million of mercury. Canned white tuna contains nearly three times higher levels (0.32 parts per million of mercury). To be eco-friendly, low-mercury tuna also needs to be certified as sustainably harvested and either pole, troll, or line-caught in the waters of the North Pacific. Read the label on the pouch or can (preferably BPA free) and check for the blue Certified Sustainable Seafood label from the Marine Stewardship Council. There is no doubt you will pay a premium for this type of tuna, but your body and our oceans will thank you.

When I'm cooking salmon, is there a way to tell when my fish is done by touch or sight? When cooking steaks, there are "rules of thumb" for touching the steak and knowing if it is rare, medium rare, or well done. I'm wondering if there is something similar for salmon.
Yes, there are “rules of thumb” for touching a steak, or burger for that matter, and knowing if it is rare, medium rare, or well done by how it “springs back” and feels firm or flabby. The same is somewhat true for salmon, but that really isn’t your trustiest method for gauging doneness in any instances. For just twelve dollars you can exponentially increase the likelihood that your fish will be cooked to near perfection. Steaks, too! Buy an instant-read thermometer and take the internal temperature of the fish in order to take the guesswork out of gauging when fish is moist, flaky, and tender. Just like a good juicy steak cooked medium rare, fish should be cooked medium rare, and that means cooking it to about 125ºF, and not above 130ºF.

I've heard that you should not marinate fish in an acid for very long. Is this true and if so why? Are there any other ingredients best left out of a fish marinade?
Yes, it is absolutely true that you should not marinate fish in an acid-based marinade for very long. As the fish sits in the marinade, the citric acid from the juice begins to “cook” the flesh. Technically, the proteins in the flesh are denatured—transformed—changing the texture and appearance, resulting in raw fish becoming opaque and firm. Ceviche is a great example.

Kenji López-Alt, food science geek and author of the award-winning cookbook, The Food Lab, wanted to study the transformation of sliced raw fish when it was marinated in straight lime juice for as little as one minute and up to one hour. At two minutes he observed textural changes in the exterior of the fish. At 10 minutes, the fish was nicely firm on the outside, but still tender and moist in the interior. He thought it was even better at 15 minutes, while at 30 minutes he assessed it as bordering on too cooked. At one hour he declared the slices to be overcooked. While this experiment used straight lime juice, other acidic marinades benefit from this analysis, concluding that 15 to 25 minutes is about the right timing to let fish marinate. The best marinades for fish are ones that don’t overpower the flavor of the fish itself. That said, depending on the fish selected, Indian, Asian, Peruvian, Italian, and Greek flavor profiles complement seafood beautifully.

What's the most sustainable stock of Salmon?
Alaska, home to abundant stocks of salmon, is the only state in the nation whose constitution explicitly mandates that all fish, including salmon, “shall be utilized, developed, and maintained on the sustained yield principle.” As a result, Alaska’s wild-caught salmon stocks rank as the healthiest and best managed in the world. Alaska was the first fishery certified as sustainable by the Marine Stewardship Council.

Is frozen seafood just as nutritious as fresh seafood?
Taste and nutrition are locked in when seafood is frozen. The quality of seafood cannot be improved once it leaves the water, it can only be maintained through superior methods of handling and cleanliness, timing, and temperature control. As time passes and ambient temperature climbs, bacterial growth increases, seafood quality diminishes, and eventually spoils.  Seafood, like other foods, needs to be frozen very quickly to prevent cellular damage. Therefore, understanding where your fish comes from and how it was handled is key to maintaining its taste and nutrition. High technology freezing is very important in achieving superior quality taste, texture, and nutrition. The best frozen seafood is rapidly chilled down and held at 32 degrees F. until it is flash frozen at a temperature no higher than – 20 degrees F. It is best protected from dehydration by being vacuum sealed or glazed (a covering of water that forms a protective sheet of ice).  And, then, the seafood should be held or transported at below 0 degrees F., resulting in a product that tastes every bit as fresh as the day it left the water.  

What words should I look for when trying to eat sustainable seafood at restaurants?
Ideally, seafood on a restaurant menu should be labeled as sustainably caught as a point of pride for the restaurant. It is reasonable for the diner to know what type of fish is being served, where it is from, and, maybe, how it was caught. The waitstaff should be trained to answer such questions. While there is widespread mislabeling of seafood sold in retail outlets and in restaurants, it is our job as consumers to be as informed as possible. As an example, if you see the description “organic Scottish salmon” on a menu, know that the salmon has been farmed in Scotland using organic practices. (Unlike the United States, the EU provides organic certification for aquaculture in Europe.) If you see the words “all-natural” or “environmentally sustainable” as descriptions for seafood, ask more questions because these terms are unregulated marketing language. Any seafood that is labeled Alaskan is indeed sustainably wild-caught since no fish farming is allowed in the state of Alaska. Using the Monterey Bay Aquarium Seafood Watch website or app, you can download their complete guide on your smartphone and have ready access to valuable information that will help inform your decisions.

What is the best way to cook rockfish?
Rockfish is a terrifically versatile fish to cook. It is mild in flavor with a texture that produces lovely, thick, coarse flakes when cooked. It is sometimes cooked as a whole fish, in the Chinese style, with scallion and ginger in a light-soy braising liquid. Cut into chunks, the fish makes a lovely addition to seafood soups, chowders, and stews. I’ve prepared rockfish baked in a tart tomato sauce—Veracruz style. It could be braised in a Thai style with green curry and coconut milk, adding a little fish sauce, lime juice, green onions and cilantro. Of course, it would be simple and delightful to marinate it briefly in a lemon juice and olive oil marinade adding fresh herbs and pepper. Bake it in a moderately hot, 425 degree F oven until it gently flakes.