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Identification of aquatic products and their products (2)
31. Identification of Contaminated Fish, Rivers, and Lakes
Due to the impact of industrial wastewater discharge, fish can become contaminated and die, often ending up in the market for sale. Identifying contaminated fish involves checking several key characteristics:
(1) Posture: Contaminated fish often appear deformed, with small heads and tails, or a small head and swollen abdomen. Their spines may be bent, and their scales might show unusual colors like yellow, red, or blue.
(2) Eyes: The eyes of contaminated fish are usually cloudy, dull, or even bulging outward.
(3) Gills: The gills of contaminated fish tend to look pale or white, lacking the natural pinkish color of healthy fish.
(4) Odor: Contaminated fish typically emit strong, unpleasant smells such as ammonia, kerosene, or hydrogen sulfide, and lack the usual fresh fishy odor.
32. Which Parts of the Pufferfish Contain Toxins?
The toxins in pufferfish are primarily found in the ovaries and liver. Additionally, some toxins may also be present in the kidneys, blood, eyes, gills, and skin. During winter and spring, the ovarian toxins are at their highest level. Even a small piece of this fish can cause poisoning if consumed.
33. Which Parts of the Carp Contain Toxins?
Also known as carp, mackerel, and similar species, these fish have black blood. When cut along the back, a visible blood line remains. This line is toxic, and washing the fish won’t remove it. Consuming it can lead to allergic reactions. If the fish has a soft, yellow belly, broken appearance, or a pasty mouth, it’s likely spoiled, and eating it could cause swelling or illness.
34. Which Parts of the Carp Contain Toxins (Blue Spot Carp)?
Known as blue spot carp or blue point carp, this fish has tender meat but contains toxins in its liver. Therefore, when cleaning, the liver must be removed to avoid poisoning.
35. Which Parts of the Pond Fish Contain Toxins?
Also called blue round, stick fish, barb, or pool fish, this fish should be eaten fresh. If left for too long, histidine in the fish breaks down into toxic ammonia, leading to food poisoning.
36. Which Parts of the Carp Contain Toxins (Beard Fish)?
Also known as carp, yubalang, and beard fish, this freshwater wild fish is found in rivers across China. While nutritious and tasty, its eggs are toxic and should be removed during cleaning.
37. Which Parts of the Carp Contain Toxins (White Peony Carp)?
Commonly found in markets, this fish is popular and affordable. However, its liver contains toxins that can cause food poisoning, so it should be removed during preparation.
38. Which Parts of the Catfish Contain Toxins?
Catfish from Qinghai Lake contain toxins in their viscera and eyes. These parts must be removed during cleaning to prevent food poisoning.
39. Which Parts of the River Eel Contain Toxins?
Also known as cockroaches, eels, and white cockroaches, river eels have toxic serum. Contact with wounds should be avoided to prevent infection and inflammation.
40. Why Should You Not Eat Dead Stingrays?
Stingrays, also known as Astragalus, are high in nutrients but must be eaten fresh. After death, histidine in their bodies turns into toxic histamine, causing food poisoning. Their blood also contains toxins that can cause wound infections if touched.
41. Why Should You Not Eat Dead Soft-Shell Turtles?
Soft-shell turtles, also known as group fish or kings, are rich in nutrients but dangerous when dead. Histidine in their bodies breaks down into histamine after death, which can cause severe allergic reactions, including shock. Eating dead turtles can lead to food poisoning.
42. Freshness Test of Aquatic Products Using Boiling
For slightly spoiled aquatic products, boiling them and observing the smell, taste, and soup can help determine freshness. The sample should not exceed 500 grams, and the water should just cover the sample. Boil, then check the odor, taste, and clarity of the broth.
(1) Smell: Fresh fish has a natural scent; spoiled fish has an ammonia or foul smell.
(2) Taste: Fresh fish is flavorful and elastic; spoiled fish lacks umami and has a slimy texture.
(3) Soup: Fresh fish produces clear, colorful broth; spoiled fish has cloudy, murky soup.
43. Rapid Freshness Test of Aquatic Products
(1) pH Measurement: Fresh fish has a pH of 6.5–6.8; slightly spoiled fish has 6.9–7.0; spoiled fish has over 7.1.
(2) Hydrogen Sulfide Test: A filter paper placed over the sample will change color depending on contamination levels.
(3) Ammonia Test: Cloudiness in the test tube indicates spoilage.
44. Quality Identification of Kelp
Good kelp is dark brown or greenish-brown, thick, and free of roots. It has a slight white powder and minimal impurities. Poor quality kelp is yellow-green, thin, and has more sand.
45. Quality Identification of Shark Fins
High-quality shark fins are large, dry, and smooth with a slight sheen. Lower-quality fins are small, thin, and less firm.
46. Quality Identification of Bird's Nest
Bird’s nests are classified into three grades: first-grade (blood nest), second-grade (white nest), and third-grade (with feathers). High-quality nests are transparent, thick, and clean.
47. Quality Identification of Dried Scallops
Dried scallops are made from shellfish muscles. High-quality ones are large, firm, and rich in protein and phosphorus. They are mainly produced in coastal areas of China.
48. Quality Identification of Dried Abalone
Dried abalone comes in different types, including purple, bright, and gray. High-quality abalone is oval, has a flower pattern, and is free of impurities.
49. Quality Identification of Dried Squid
Top-grade dried squid has a pink flesh, is large, and has a complete body shape. Lower grades are smaller and less firm.
50. Quality Identification of Dried Shrimp
Top-grade shrimp are bright yellow or red, have no impurities, and are firm. Poor-quality shrimp are dull, have a salty taste, and are small.
51. Quality Identification of Dried Mussels
Dried mussels come in four sizes. High-quality ones are large, uniform, and have a fresh taste. Low-quality mussels are small, discolored, and have impurities.
52. Quality Identification of Fish Maw
Fish maw is made from fish swim bladders. High-quality maw is thick, shiny, and intact. Spoiled maw is thin, dark, and has an odd smell.
53. Quality Identification of Fish Skin
Fish skin is made from shark or croaker skins. High-quality skin is thick, clear, and free of dirt. Low-quality skin is thin, discolored, and has a salty taste.
54. Quality Identification of Dried Oyster Stems
Dried oyster stems are classified into three grades based on size and quality. High-quality stems are large, golden, and have a good texture. Low-quality stems are small, dark, and have a bad smell.
55. Color Changes in Dried Seafood
Dried seafood can change color due to poor storage, leading to spoilage. This is caused by salt-tolerant bacteria. To prevent this, store in cool, dry places and ensure proper packaging.
56. Causes of Rancidity in Dried Seafood
Long-term storage can cause fat oxidation, resulting in bitterness and discoloration. To prevent this, store in cool, dry places and avoid exposure to sunlight.
57. Mold Prevention in Dried Seafood Storage
Insects can damage dried seafood. To prevent infestation, maintain cleanliness, use insecticides, and store in cold conditions.
58. Principles of Sensory Identification and Consumption of Aquatic Products
Aquatic products spoil quickly due to high protein and moisture content. Fresh products should be consumed immediately. Sub-fresh products should be sold quickly, and spoiled ones should not be used for consumption.
59. Identification of Artificial and Natural Jellyfish
Artificial jellyfish is brittle and lacks elasticity, while natural jellyfish is firm, shiny, and has a crunchy texture.
60. Identification of Real Crab Meat vs. Artificial Crab Meat
Real crab meat does not show colored patterns under light, while fake crab meat made from salmon or other fish may show stripes. Use a microscope to detect artificial additives.
61. Identification of Cultured Shrimp vs. Wild Shrimp
Cultured shrimp have softer textures and shorter bodies, while wild shrimp are firmer and have shorter, blunter heads. Consumers should be cautious of mislabeled products.
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