How can easily confused species of premium fish be accurately identified?

With the development of the socialist market economy and the improvement of people's living standards, fisheries production has taken a new leap forward. In particular, in recent years the development of premium fish has been extremely rapid. However, because some premium fish are extremely similar in appearance and rather difficult to distinguish, this has caused certain difficulties for farmers and consumers in purchasing and identifying them. The identification methods for currently easily confused species of premium fish are presented below for reference. 1. Yellow catfish (Pelteobagrus fulvidraco), long-barbel yellow catfish, darkbarbel catfish (Pelteobagrus vachelli), and glossy yellow catfish. Among these four fish, the pectoral fin hard spines of yellow catfish and long-barbel yellow catfish have obvious serrations on both the front and rear edges. The yellow catfish has a short and stout body, usually with a body length 4.2 times or less the body depth, and the predorsal distance is greater than 1/3 of the body length; the long-barbel yellow catfish has a relatively longer and slightly slender body, usually with a body length 4.6 times or more the body depth, and the predorsal distance is less than 1/3 of the body length; while the pectoral fin hard spines of darkbarbel catfish and glossy yellow catfish are smooth on the front edge and have strong serrations on the rear edge; the darkbarbel catfish has skin covering the top of the head, longer barbels, and the end of the maxillary barbel can extend backward to the origin of the pectoral fin; the glossy yellow catfish has most of the top of the head bare, shorter barbels, and the end of the maxillary barbel slightly passes the posterior margin of the eye. 2. Southern sheatfish (Silurus meridionalis), catfish (Silurus asotus), and airbreathing catfish (Clarias fuscus). The airbreathing catfish has very long dorsal and anal fins that extend backward to the caudal fin, and has four pairs of barbels, including 1 pair of nasal barbels, 1 pair of maxillary barbels, and 2 pairs of mental barbels. Both the catfish (called local catfish in some places) and the southern sheatfish have very short and small dorsal fins. Their identification methods are as follows: the southern sheatfish has a large mouth cleft, with its end at least opposite the middle of the eyeball; its pectoral fin hard spine is relatively smooth on the front edge without obvious serrations; the upper lobe of the caudal fin is obviously longer than the lower lobe; the color of the back and sides of the body is uniform, with no markings on the back; juvenile fish have black spots on the ventral surface of the head; adults have 2 pairs of oral barbels, and juveniles with a body length of 10 cm to 15 cm have a second pair of mandibular barbels; sexual maturity is usually reached only at 3 to 4 years of age and over 3 kg, and mature eggs are oily yellow. The catfish has a small mouth cleft, with its end only opposite the anterior margin of the eye; the front edge of the pectoral fin hard spine has obvious serrations; the notch between the upper and lower lobes of the caudal fin is such that the upper and lower lobes are equal in length and remain symmetrical; the back and sides of the body have alternating dark and light colors and irregular cloud-like spots; it has 2 pairs of barbels, with the maxillary barbels longer and the mental barbels shorter; it reaches sexual maturity at 1 to 2 years of age and about 75 g, and mature eggs are grass green. 3. Snakehead (Channa argus), spotted snakehead (Channa maculata), and Chinese snakehead (Channa asiatica). Among these three fish, the Chinese snakehead is very easy to identify because it lacks pelvic fins. The snakehead has a relatively long body, a head and back with a "seven-star" pattern, and 63 to 69 lateral line scales; while the spotted snakehead has a relatively short body, a head and back with a "one-eight-eight" pattern, and 58 to 60 lateral line scales. 4. Mandarin fish (Siniperca chuatsi) and bigeye mandarin fish (Siniperca kneri). There are many species of mandarin fish, altogether 3 genera and 10 species, with the most common being the mandarin fish (also called topmouth culter-like mandarin fish) and the bigeye mandarin fish. Their distinguishing methods are as follows: 1. The size of the eyes differs: the mandarin fish has smaller eyes, while the bigeye mandarin fish has larger eyes; 2. The position reached by the maxilla differs: the maxilla of the mandarin fish extends below and behind the posterior margin of the eye, while the maxilla of the bigeye mandarin fish only extends below and in front of the posterior margin of the eye; 3. The growth rate differs: under the same conditions, the growth rate of the mandarin fish is more than 4 times that of the bigeye mandarin fish. Note, however, that at the fry and fingerling stage the growth rates of the two fish are almost the same. 5. Japanese eel, European eel, American eel, and Australian eel. These four eels can be identified by drug testing. When soaked in a 0.46 g/cubic meter solution of butylene phosphonate, the Japanese eel will not die within 1 hour, while the others all die. They can also be tested with "Ou Qing Tian" by measuring the 24-hour lethal concentration: Japanese eel 6 g/cubic meter, European eel 0.4 g/cubic meter. 6. Siberian sturgeon, Amur sturgeon, Danube sturgeon, Chinese sturgeon, naked-belly sturgeon, sterlet, Missouri shovel sturgeon, Mississippi shovel sturgeon, Yangtze paddlefish, and spoonbill paddlefish. The Siberian sturgeon has a body with 5 rows of bony plates, 4 rostral barbels, a spiracles on the head, a small mouth cleft that does not reach the side of the head, gill membranes that are not connected, bony plates on the dorsal surface of the snout, cylindrical barbels, and fewer than 58 bony plates on the sides of the body; the lower lip is interrupted in the middle; the Amur sturgeon has a complete lower lip and fewer than 40 dorsal fin rays; the Danube sturgeon has more than 40 dorsal fin rays, gill rakers that are triangular and lamellar and closely arranged, and rough skin in juveniles; the Chinese sturgeon has gill rakers that are short and columnar and sparsely arranged, and smooth skin in juveniles; the naked-belly sturgeon has more than 58 bony plates on the sides of the body; the lower lip is complete; the sterlet has the lower lip interrupted in the middle; the kaluga has a large mouth cleft, sometimes reaching the side of the head, connected gill membranes, cartilage on the dorsal surface of the snout, and laterally compressed barbels; the Missouri shovel sturgeon has no spiracles, a bare abdomen, more than 37 dorsal fin rays, and fewer than 24 anal fin rays; the Mississippi shovel sturgeon has small dermal plates on the abdomen, more than 36 dorsal fin rays, and fewer than 23 anal fin rays; the Yangtze paddlefish has a bare body with spinous hard scales only on the upper lobe of the caudal fin, 2 rostral barbels, a protrusible mouth, and a conical sword-shaped snout; the spoonbill paddlefish has a non-protrusible mouth and a flat snout. In addition, some other premium fish are similar in appearance and also require attention for identification when purchasing or consuming, otherwise unnecessary losses may be caused.