Ch.4: Fish and Shellfish

Chapter 4 of the book "On Food and Cooking: The Science and Lore of the Kitchen" by Harold McGee (1984) Fisheries and Aquaculture Seafood and Health Life in Water and the Nature of Fish The Anatomy and Qualities of Fish The Fish We Eat From the Waters to the Kitchen Unheated Preparations of Fish How Heat Transforms Raw Fish Preparations for Cooking Techniques for Cooking Fish Fish Mixtures Shellfish and Their Special Qualities Crustaceans Molluscs Other Invertebrates: Sea Urchins Preserved Fish and Shellfish Dried Fish Salted Fish Fermented Fish Smoked Fish Japanese Katsuobushi Marinated Fish Canned Fish Fish Eggs Salt Transforms Egg Flavor and Texture Caviar

326 flashcards · Other · by lakesare

Part of Public › Books › On Food and Cooking (Harold McGee) · 16 courses

1. [Fish and Shellfish] How old are the oldest known heaps of oyster and mussel shells left from human meals?

   About 300,000 years. By 40,000 years ago, hunters in Europe carved images of salmon and made the first fish hooks.

2. [Fish and Shellfish] Why have the ocean's fish stocks been exhausted?

   Ten times more people, fishing with ever more efficient technology. Example: larger and faster ships, sonar, nets and lines miles long. Cod, herring, Atlantic salmon, swordfish, sole, sturgeon and shark have become rare.

3. [Fish and Shellfish] Which seafoods come almost entirely from farms?

   Freshwater fish, Atlantic salmon and mussels. As of 2004.

4. [Fish and Shellfish] Why are fish and shellfish harder to cook well than ordinary meats?

   They are more fragile and less predictable, and come in great variety.

5. [Fisheries and Aquaculture] What is unique about fish and shellfish among all our foods, in terms of where they come from?

   They are the only food still harvested in significant quantities from the wild.

6. [Fisheries and Aquaculture] What did the biologist T. H. Huxley claim about the great sea fisheries in 1883?

   That they were inexhaustible: nothing people do would seriously reduce the numbers of fish. About a century later the cod and herring stocks of the North Atlantic collapsed. The U.N. Food and Agriculture Organization estimates that two-thirds of the major commercial fish are harvested at or beyond the level they can sustain.

7. [Fisheries and Aquaculture] What is bycatch?

   Animals of non-target species caught by unselective nets and lines and simply thrown away.

8. [Fisheries and Aquaculture] Fish farming is called aquaculture.

   About 70 species are farmed worldwide. In the U.S., all rainbow trout and nearly all catfish sold are farmed on land in ponds and tanks.

9. [Fisheries and Aquaculture] What are the main advantages of aquaculture for the quality of fish?

   Control over the fish Fish can be bred for fast growth and harvested at a uniform, ideal stage. Example: water temperature, flow and light are set to speed growth while giving the muscle some exercise. Fattier flesh Farmed fish are often fattier and so more succulent. Better harvest No stress or damage from hooks, nets or being dumped on deck; immediate clean processing and chilling. This prolongs the period of top quality.

10. [Fisheries and Aquaculture] What are the main environmental drawbacks of aquaculture?

    Pollution Offshore pens release wastes, antibiotics and uneaten feed into the surrounding water. Escapes Escaped, genetically uniform farmed fish dilute the genetic diversity of endangered wild populations. Feed from wild fish Carnivorous and scavenging species are fed mainly fish meal, so their farms consume wild fish. Example: salmon and shrimp. Toxins PCBs become concentrated in fish meal, and from there they accumulate in the flesh of salmon raised on farms.

11. [Fisheries and Aquaculture] How do farmed trout, salmon and catfish compare with wild ones in taste tests?

    Farmed fish are perceived as blander and softer. Causes: limited water flow, limited exercise and artificial feed.

12. [Fisheries and Aquaculture] Which kinds of fish farming harm the environment least?

    Fish farmed on land, and molluscs (such as mussels) farmed on seacoasts. Example: freshwater fish, and the saltwater sturgeon and turbot, farmed in tanks and ponds.McGee's assessment (2004).

13. [Seafood and Health] What is the simplest way to minimize the health hazards of seafood?

    Buy from a busy specialist shop, and cook the seafood soon and all the way through. A busy shop sells its stock quickly, so the seafood is fresher.Raw and lightly cooked seafood is best eaten at established restaurants with access to the best fish.

14. [Seafood and Health] Besides protein and B vitamins, which two minerals are special nutritional strengths of fish and shellfish?

    Iodine and calcium.

15. [Seafood and Health] What does the name omega-3 fatty acid mean?

    The first double bond (kink) of the carbon chain is at the third carbon from the end of the chain. Ocean fish fats are rich in these highly unsaturated fatty acids. The human body makes them only inefficiently, so they come mostly from the diet.

16. [Seafood and Health] Where do fish get their omega-3 fatty acids from?

    From phytoplankton (tiny ocean plants), eaten directly or via other animals. So freshwater fish provide negligible omega-3s, and farmed fish usually less than wild, since their feed has less.

17. [Seafood and Health] What is the direct benefit of omega-3 fatty acids for the body?

    The brain and the retina need them, both to develop and to work.

18. [Seafood and Health] How do omega-3 fatty acids protect against heart disease?

    The body turns them into signal molecules (eicosanoids) that calm inflammation, which otherwise can damage arteries. They also reduce blood clotting (fewer strokes) and lower the artery-damaging form of blood cholesterol. McGee (2004) also credits them with lowering cancer rates, by limiting inflammation.

19. [Seafood and Health] Why does eating fish instead of meat lower blood cholesterol, even if the fish is freshwater and has no omega-3s?

    All fish contain little saturated fat, the fat that raises blood cholesterol.

20. [Seafood and Health] Which industrial pollutants in fish are the most significant?

    Heavy metals (mercury, lead, cadmium, copper) and organic pollutants (dioxins, PCBs). Heavy metals interfere with oxygen absorption and nerve signals and cause brain damage. Organic pollutants accumulate in body fat and cause liver damage, cancer and hormonal disturbances in lab animals.

21. [Seafood and Health] In which two kinds of seafood do chemical toxins concentrate most?

    Filter-feeding shellfish They strain particles out of large volumes of water. Example: oysters. Large predatory fish They live long and eat other animals that have accumulated toxins. Example: swordfish, shark. Cooking does not remove chemical toxins.

22. [Seafood and Health] Because of mercury, which fish did the U.S. FDA (2004) advise children and pregnant women not to eat at all?

    Swordfish, shark, tilefish and king mackerel. Their total fish should be limited to 12 ounces (335 g) per week.

23. [Seafood and Health] Which fish are least likely to accumulate mercury and other toxins?

    Small, short-lived fish from the open ocean, and fish farmed with a controlled water supply. Example: Pacific salmon, sardines, common mackerel; farmed trout, catfish and tilapia.

24. [Seafood and Health] Why are raw or undercooked bivalves the riskiest seafood for infections?

    They filter bacteria and viruses out of the water, and we eat them whole, gut included, often raw. Bivalves (oysters, clams, mussels) feed by straining large volumes of water.In the 19th century outbreaks of cholera and typhoid fever were already traced to shellfish from polluted waters.

25. [Seafood and Health] To what temperature must seafood be cooked to prevent infection by bacteria and parasites?

    At least 60°C (140°F). Some toxins made by microbes survive cooking even though the microbes are destroyed.

26. [Seafood and Health] What temperature is needed to eliminate some viruses in seafood?

    Above 82°C (185°F). Bacteria and parasites are already killed at 60°C (140°F).

27. [Seafood and Health] Which microbes in seafood are the most important causes of disease?

    Vibrio bacteria Live in estuaries and multiply in warm months. One species causes cholera; V. vulnificus, usually from raw oysters, is the deadliest seafood disease. V. vulnificus causes high fever, a drop in blood pressure and skin and flesh damage, and more than half of the people infected die. Botulism bacteria Grow in the gut of unchilled fish and produce a deadly nerve toxin. Example: most fish-borne cases come from badly cold-smoked, salt-cured or fermented products. Norwalk viruses Attac…

28. [Seafood and Health] What causes scombroid poisoning?

    Toxins, including histamine, made by otherwise harmless microbes that grow on fast-swimming fish kept too warm. Example: mackerels (genus Scomber, hence the name), tuna, mahimahi, bluefish, herring, sardine, anchovy.

29. [Seafood and Health] What are the symptoms of scombroid poisoning?

    Headache, rash, itching, nausea and diarrhea, within half an hour of eating the fish, even if it was fully cooked. The symptoms pass. Antihistamines give some relief.

30. [Seafood and Health] Which organisms produce the toxins behind shellfish poisonings?

    Dinoflagellates: one-celled algae. At least 60 species make such toxins, as a chemical defense.

31. [Seafood and Health] How do the algal toxins behind shellfish poisonings get into shellfish?

    Bivalves filter the algae out of the water and concentrate the toxins in their gills or digestive organs. From bivalves the toxins pass to us, or to crabs and whelks that eat bivalves.

32. [Seafood and Health] Why should shellfish suspected of algal toxins be avoided rather than cooked thoroughly?

    Dinoflagellate toxins are not destroyed by ordinary cooking; some even become more toxic when heated. Most types cause tingling, numbness and weakness within minutes to hours. The greatest risk is from privately gathered shellfish, since commercial waters are monitored.

33. [Seafood and Health] Fish rarely carry toxins from algae. Which fish are the exception, causing ciguatera poisoning?

    Tropical reef fish that eat a snail (cigua) which feeds on toxic algae. Example: barracuda, groupers, jacks, snappers, mahimahi, king mackerel.

34. [Seafood and Health] Why does freezing eliminate parasites in fish but not bacteria?

    Parasites are animals with a more complex biological organization, which freezing damages; bacteria generally survive freezing. More than 50 parasites can be passed to people from raw or undercooked fish.

35. [Seafood and Health] What freezing treatments does the U.S. FDA recommend to eliminate parasites in fish?

    −35°C (−31°F) for 15 hours, or −23°C (−10°F) for seven days. Home freezers seldom go below −18°C (0°F), so they can't do this. The alternative is cooking to at least 60°C (140°F).

36. [Seafood and Health] What are anisakid and cod worms?

    Roundworms about 2.5 cm long that sometimes invade the stomach or intestinal lining, causing pain, nausea and diarrhea. Found in cod, halibut, herring, mackerel, rockfish, salmon and squid; contracted from sushi and lightly marinated, salted or cold-smoked fish. Farmed salmon are much less often infected than wild.

37. [Seafood and Health] Which tapeworm is carried by freshwater fish of temperate regions?

    Diphyllobothrium latum, which can grow to 9 m long in the human intestine.

38. [Seafood and Health] How did cooks making gefilte fish (a Jewish dish of chopped fish bound with eggs) often catch tapeworms?

    They tasted the raw whitefish mixture to check its seasoning.

39. [Seafood and Health] How can cooks minimize the formation of potential carcinogens when cooking fish?

    Steam, braise or poach rather than grill, broil or fry; with high dry heat, use a marinade. The marinade's moisture and acidity reduce carcinogen formation.

40. [Life in Water and the Nature of Fish] Why do fish have light bones and little, delicate connective tissue compared with land animals?

    Water is dense: storing a little oil or gas makes fish nearly weightless, so they need no heavy support against gravity. Land animals need heavy skeletons and tough connective tissue to support themselves.

41. [Life in Water and the Nature of Fish] Why is most fish muscle white?

    Most of it is fast-twitch white fibers, used only for occasional bursts of speed. Cruising in buoyant water takes little effort, so only a tenth to a third of the muscle is slow red fiber, usually a thin dark layer under the skin. But water's resistance rises steeply with speed, so accelerating needs a large mass of fast muscle. Cross-sections: a typical fish (mostly white, small dark regions), a tuna (large dark regions), a flatfish.

42. [Life in Water and the Nature of Fish] What are the "pink" muscle fibers of tunas?

    White fibers modified for continuous work, containing oxygen-storing pigment.

43. [Life in Water and the Nature of Fish] How salty is open ocean water, compared with the inside of animal cells?

    About 3% salt by weight, versus under 1% dissolved minerals inside cells.

44. [Life in Water and the Nature of Fish] How do most ocean animals balance the saltiness of seawater inside their cells?

    They fill their cells with amino acids and amines. This makes them tasty. Example: glycine tastes sweet, glutamate savory. Shellfish are especially rich in such amino acids.

45. [Life in Water and the Nature of Fish] Besides amino acids, which largely tasteless substance do ocean finfish use to balance the saltiness of seawater?

    TMAO (trimethylamine oxide).

46. [Life in Water and the Nature of Fish] Which substance do sharks, skates and rays use to balance the saltiness of seawater?

    Urea, the usual form in which animals get rid of protein waste. It tastes slightly salty and bitter.

47. [Life in Water and the Nature of Fish] Why does old ocean fish smell bad?

    After death, bacteria and fish enzymes turn its TMAO (trimethylamine oxide) into smelly TMA (trimethylamine).

48. [Life in Water and the Nature of Fish] Why does old shark meat smell of ammonia?

    After death, bacteria and enzymes turn the urea in its flesh into ammonia. Sharks, skates and rays keep urea in their cells to balance the saltiness of seawater.

49. [Life in Water and the Nature of Fish] Why is the flesh of freshwater fish milder than that of ocean fish, both fresh and old?

    Fresh water is less salty than their cells, so they don't accumulate amino acids, amines or urea.

50. [Life in Water and the Nature of Fish] Why are fish fats much more unsaturated than beef fat?

    Ocean fish and plankton live near 0°C, and their fats must stay fluid there, so their fatty acids are very long and irregular. Beef fat is made for a body temperature near 40°C; in cold ocean water it would solidify.

51. [Life in Water and the Nature of Fish] For what two reasons does the cold of their habitat make fish spoil faster than meat?

    Their highly unsaturated fats are easily oxidized; and their enzymes and bacteria work well in the cold, so a refrigerator (5°C) barely slows them. The enzymes and bacteria of warm-blooded animals work at about 40°C and are very slow at 5°C.

52. [Life in Water and the Nature of Fish] Why do fish overcook more easily than meat?

    Their muscle proteins are adapted to the cold, so they also denature at lower temperatures. McGee: "The muscle proteins of ocean fish begin to unfold and coagulate at room temperature!"

53. [Life in Water and the Nature of Fish] Why does cooked fish fall apart so easily?

    Fish has little collagen, and it dissolves into gelatin at a low temperature. For the same reason, overcooked fish gets dry but never tough.

54. [Life in Water and the Nature of Fish] Why does the quality of many wild fish vary drastically with the season?

    Before spawning, many fish digest their own muscle to make eggs or sperm. They store energy as muscle protein, not as fat, and also use it up during migration.Muscle enzymes break down the proteins, leaving the flesh meager, spongy and mushy, during and after spawning.

55. [The Anatomy and Qualities of Fish] What is the basic body plan of most fish, unchanged for about 400 million years?

    Sheets of muscle anchored by connective tissue and the backbone to a propulsive tail, in a streamlined shape. The fish push water behind them by undulating the whole body and flexing the tail.

56. [The Anatomy and Qualities of Fish] Why does fish skin give much more gelatin to stocks than the flesh does?

    Its thick dermis is about one-third collagen by weight, versus 0.3 to 3% in the flesh. Moist heat turns skin into a slick gelatinous sheet; frying or grilling that dries it makes it crisp. Skin averages 5 to 10% fat.

57. [The Anatomy and Qualities of Fish] What are fish scales made of?

    The same hard calcium minerals as teeth.

58. [The Anatomy and Qualities of Fish] What are the "pin" (floating) bones of fish?

    Small bones not attached to the main skeleton, which stiffen the connective-tissue sheets. Example: fish of the herring and salmon families have them.

59. [The Anatomy and Qualities of Fish] Why can fish bones be softened by a short time near the boil, unlike the bones of land animals?

    They are smaller, lighter, less mineralized with calcium, and their collagen is less tough. Example: canned salmon is rich in calcium because its bones soften during canning.

60. [The Anatomy and Qualities of Fish] What are fish sounds?

    Swim bladders: sacs of connective tissue that fish fill with air to adjust their buoyancy. Example: cod, carp, catfish, sturgeon. In Asia they are dried, fried until puffed, then simmered in a sauce.

61. [The Anatomy and Qualities of Fish] What are the cod and carp "tongues" sold as food?

    Throat muscles with their connective tissue, which softens with long cooking.

62. [The Anatomy and Qualities of Fish] How is fish muscle structured, unlike the long muscles of land animals?

    Short fibers arranged in thin sheets (myotomes), separated by very thin layers of connective tissue (myosepta) that run from backbone to skin. The sheets are folded in W-like shapes. A cod has about 50 of them along its length: the flakes of cooked fish. Layers of short muscle fibers, separated by thin sheets of connective tissue.

63. [The Anatomy and Qualities of Fish] For what two reasons is fish connective tissue weak?

    Its collagen has fewer reinforcing amino acids than beef collagen; and fish muscle is repeatedly built up and broken down as an energy store. In land animals, connective tissue is progressively reinforced with age.

64. [The Anatomy and Qualities of Fish] At what temperature does the collagen of most fish dissolve into gelatin?

    About 50 to 55°C (120 to 130°F). The muscle layers then separate into flakes. Meat collagen dissolves only after a fairly long time close to the boil.

65. [The Anatomy and Qualities of Fish] What two substances make cooked fish seem moist?

    Gelatin and fat. Example: halibut and shark (more collagen) seem moister than trout and bass (less collagen).

66. [The Anatomy and Qualities of Fish] Why does the tail end of a fish have more succulent flesh than the head end?

    It contains more connective tissue (gelatin), since the steady swimming motion comes mostly from the back end.

67. [The Anatomy and Qualities of Fish] Why does dark fish meat have a finer, more gelatinous texture than white?

    Red fibers are thinner, so more connective tissue is needed to join them.

68. [The Anatomy and Qualities of Fish] How much fat does fish muscle contain?

    From 0.5% (cod) to 20% (well-fed herring). Example: cod and sole are lean (under 3%); Atlantic and king salmon, herring and bluefin tuna are fatty (8% or more).

69. [The Anatomy and Qualities of Fish] Where in a fish is its fat stored?

    Mostly in a layer under the skin, then in the connective-tissue sheets between the muscle layers. The belly is fattiest and the muscle gets leaner towards the tail. Example: a center-cut salmon steak can have twice the fat of a slice from the tail.

70. [The Anatomy and Qualities of Fish] For what two reasons can fish flesh become mushy?

    Depletion After migration or spawning, the sparse muscle proteins bond to each other only loosely. Example: "sloppy" cod or "jellied" sole, whose muscle seems almost liquid. Freezing Freezing breaks cell compartments and frees enzymes, which attack the muscle fibers after thawing.

71. [The Anatomy and Qualities of Fish] Why does ocean fish taste fuller than meat or freshwater fish?

    Its content of free amino acids is three to ten times higher, with about the same amount of sodium. The most notable of these are glycine, which tastes sweet, and glutamate, which tastes savory.So fish from less salty water, e.g. near river mouths, tastes less intense.

72. [The Anatomy and Qualities of Fish] Why does the savoriness of fish first rise and then fall in the time after death?

    The energy carrier ATP breaks down into IMP (inosine monophosphate), which tastes savory like glutamate; IMP then breaks down further.

73. [The Anatomy and Qualities of Fish] Why does very fresh fish smell like crushed leaves?

    Fish and leaves have similar fats and enzymes, which break the fats into the same aroma molecules. Both have highly unsaturated fats and lipoxygenase enzymes.Nearly all fish produce 8-carbon fragments with a geranium-leaf, slightly metallic smell; freshwater fish also cut-grass (6 carbons) and mushroom (8 carbons) notes; smelts melon and cucumber (9 carbons).

74. [The Anatomy and Qualities of Fish] Which compounds give ocean fish the smell of the seacoast?

    Bromophenols, which algae and some primitive animals make from the bromine in seawater. Fish take them up by eating algae or algae eaters. Farmed saltwater fish lack this aroma unless bromophenols are added to the feed.

75. [The Anatomy and Qualities of Fish] Which compounds cause the muddy flavor of pond-raised catfish and carp?

    Geosmin and methylisoborneol, made by blue-green algae, especially in warm weather.

76. [The Anatomy and Qualities of Fish] How can the muddy flavor of catfish or carp be reduced?

    Cut away the skin and dark muscle, where the muddy compounds collect, and cook with acid such as vinegar, which breaks down geosmin.

77. [The Anatomy and Qualities of Fish] Which substance is the main cause of the "fishy" smell?

    TMA (trimethylamine), made by bacteria on the fish surface from TMAO. Stale, cheesy products of oxidized fats add to the fishiness. In frozen storage, fish enzymes turn some TMA into DMA, which smells weakly of ammonia.

78. [The Anatomy and Qualities of Fish] Why do freshwater fish and crustaceans get less fishy-smelling than ocean fish?

    Freshwater fish contain no TMAO and crustaceans little, so bacteria can make little smelly TMA from it.

79. [The Anatomy and Qualities of Fish] How do lemon juice, vinegar or tomatoes reduce the smell of fish past its prime?

    The acid gives TMA a hydrogen ion; the charged TMA bonds to water and does not evaporate into the air. Acid also makes stale fat fragments react with water and become less volatile. Rinsing in tap water removes surface TMA.

80. [The Anatomy and Qualities of Fish] Why is raw fish muscle translucent, compared with raw beef or pork?

    It has little connective tissue and fat around its cells to scatter light. Fatty parts such as salmon and tuna belly look milky even raw.

81. [The Anatomy and Qualities of Fish] Why does fish flesh turn opaque when it is cooked or marinated in acid?

    Heat and acid unfold its proteins, which bond to each other into large masses that scatter light.

82. [The Anatomy and Qualities of Fish] What gives tuna flesh its red color?

    Myoglobin, the oxygen-storing pigment.

83. [The Anatomy and Qualities of Fish] Why must tuna be frozen well below −30°C (−22°F)?

    Down to −30°C its myoglobin readily oxidizes to brown metmyoglobin, so the red color is lost.

84. [The Anatomy and Qualities of Fish] Why does pink raw albacore or mahimahi turn as white as white fish when cooked?

    Its little myoglobin turns gray-brown, and the milky white of the other cooked proteins hides it. Myoglobin denatures at 60 to 70°C.

85. [The Anatomy and Qualities of Fish] What gives salmon flesh its color?

    Astaxanthin, a relative of carotene, from the small crustaceans the salmon eat, which make it from algal beta-carotene. Only the salmon family stores astaxanthin in muscle. Farmed salmon are pale unless their feed is supplemented, with crustacean shell by-products or synthetic canthaxanthin.

86. [The Fish We Eat] How many fish species are there, compared with other vertebrates?

    About 29,000 species: more than half of all vertebrates.

87. [The Fish We Eat] Why do herring-family fish (herring, anchovy, sardine, sprat, shad) deteriorate so fast that most are smoked, salted or canned?

    Constant swimming and plankton feeding give them very active muscle and digestive enzymes; and they are very fatty, with easily oxidized fats. The fat content reaches 20% or more before spawning.

88. [The Fish We Eat] Which traits of carp make them ideal for aquaculture?

    They tolerate stagnant water, low oxygen and temperatures from just above 0°C to 38°C. China began farming carp three thousand years ago. The carp family is now the largest fish family (about 2,000 species).

89. [The Fish We Eat] What advantage do catfish have over carp as farmed fish?

    A simpler skeleton, which gives boneless fillets easily. They also keep well: up to three weeks vacuum-packed on ice. Both can taste muddy, mainly in late summer and fall.

90. [The Fish We Eat] Why do commercial fishermen catch salmon near the mouth of their home river?

    Then the fish are at peak quality: the upstream migration and egg production consume nearly half their weight, leaving the flesh mushy and pale.

91. [The Fish We Eat] What is the relation between salmon and trout?

    Trouts evolved from landlocked groups of Atlantic and Pacific salmon. Salmon are born in fresh water, mature in the sea, and return to their home streams to spawn.

92. [The Fish We Eat] Which salmon species are the fattiest?

    Atlantic (14% fat) and king (12%). Sockeye 10%, coho 7%, and the leanest, chum and pink, 4%. Pink salmon is mostly canned; chum is used for roe and pet food.

93. [The Fish We Eat] What may contribute to the distinctive aroma of cooked salmon?

    Its astaxanthin pigment, which on heating gives volatile molecules found in fruits and flowers.

94. [The Fish We Eat] Why is trout flesh not pink like salmon?

    Trout don't eat the pigmented ocean crustaceans that color salmon. Farmed rainbow trout take one year from egg to a single-portion fish of 225 to 450 g.

95. [The Fish We Eat] What is a farmed steelhead?

    A rainbow trout raised in salt water, which gets the pink flesh and flavor of a small Atlantic salmon.

96. [The Fish We Eat] Why does cod have mild, stable flavor and texture?

    Cod-family fish stay near the bottom and swim little, so their enzyme systems are relatively inactive. Cod set the European standard for white fish: mild, firm, large flakes, nearly free of red muscle and fat.

97. [The Fish We Eat] Which freshwater fish, unusually, produce TMAO and so can smell fishy?

    Nile perch and tilapia. Both are African fish, farmed widely as substitutes for cod and flatfish fillets.

98. [The Fish We Eat] What fish is sold as "Chilean sea bass"?

    The Patagonian toothfish, a fatty Antarctic "cod icefish". Its flesh can be nearly 15% fat. Like other deepwater fish it reproduces slowly and is being overfished.

99. [The Fish We Eat] Why is tuna flesh as dark red as beef?

    Tunas swim constantly (up to 70 km/h), so even their fast white fibers are full of myoglobin and have active energy enzymes. So tuna also has a rich, savory flavor like beef.

100. [The Fish We Eat] What reaction produces the meaty aroma of cooked and canned tuna?

     Ribose (a sugar) reacting with cysteine (a sulfur amino acid), giving an aroma compound typical of cooked beef.