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First, biological characteristics
1.External morphological characteristics Cobia fish body is elongated, nearly cylindrical, slightly lateral. Head flat, wider than tall. Eyes are smaller, located on both sides of the head, and the upper edge of the head is a few and there is no fat film. The mouth is large, the front position, and the jaw is slightly longer than the upper jaw. The upper and lower jaws, the vomer, the sacrum, and the tongue surface all have villous tooth bands. The front humeral edge is smooth. The body, cheeks, upper edge of the lid, top of the head, and fins are all covered with small round scales. The lateral lines are slightly corrugated. Short and thick. The pylorus is small in size and numerous in size. Innocent. The back of the body is dark brown and the belly is greyish white. Its fins are black, but the pelvic fins and the upper and lower edges of the caudal fins are white.
2. Food habits In the natural sea area, smaller cobia mainly feed on shrimps, crabs, and cephalopods. Shrimp, crab, and cephalopods account for about 80% of the total food, followed by fish. For cobia that are more than 1 meter in length, fish is mainly eaten, and fish accounts for 80% of its total food. Cobia can be artificially fed in artificial pellets under artificial breeding conditions.
3. Temperature-appropriate army caos are tropical sea fish that are not resistant to low temperatures. After testing, the suitable water temperature for embryonic development is between 24°C and 31°C; at the larval stage (body weight between 10g and 15g), the water temperature is as low as 20°C to 21°C, the food consumption is significantly reduced, and no feeding at 19°C, 17°C～18 °C activity weakened, remained at the bottom of the water, and began to die at 16°C. The water temperature was 22°C to 34°C. There was significant feeding activity. When the water temperature rose to 36°C, it started to die despite feeding.
4. Saline-tolerance salty fish, suitable salinity 8 ‰ to 35 ‰. Larger cobia have lower endurance to low salinity, with salinity less than 8 phr, ie no feeding activity. For food fish farming, seawater salinity should be maintained at 10 ‰ or more.
5. Oxygen consumption After testing, the average weight of 0.5 g of fry, when the water temperature is 30 °C, the oxygen consumption is 1.08 mg/gh, the lethal dissolved oxygen amount is 1.7 mg/L; when the water temperature is 28 °C, the oxygen consumption is 0.86 mg In grams per hour, the lethal dissolved oxygen was 1.5 mg/l. Under normal circumstances, when the water temperature is higher, the oxygen consumption is relatively increased; the larger the individual, the higher the oxygen consumption.
6. Genital habits
(1) Male and female characteristics and the smallest body size of sexual maturity In the reproductive season, the black and white stripes on the back of the cobia females will become more pronounced, the abdomen will be prominent, and the stripes of mature males will not be obvious or disappear, and the abdomen will be smaller. However, judging from the body color is not always accurate, but it is still necessary to supplement the body shape for judgment. In cage-raised cobia, sexual maturity varies from place to place. The Zhanjiang area is 2 years old. The male body weight is more than 7 kilograms and the female body weight is more than 8 kilograms. The relative amount of eggs is 1 kg body weight 160,000 capsules, the smaller the egg size.
(2) Spawning season In the natural sea area, cobia is a spawning fish that has a long reproductive period. It can be found from April to October in the northern Gulf of Mexico off the east coast of the United States. In southern Taiwan, the peak of spawning occurred from the end of February to May, and spawning was sparse until October. Suitable spawning temperature is 24°C to 29°C.
Second, artificial breeding
1. Artificial oxytocin should be selected from the broodstock, which has a large abdomen and reveals the outline of gonads. Oxygen production uses luteinizing hormone-releasing hormone analogues (LRH-A2), human chorionic gonadotropin (HCG), and domoxone (DOM), two injections in the pectoral fin base part of the broodstock, which accounts for 1/1 of the total 3, the second time accounts for 2/3 of the total. Some broodstocks with loose belly and obvious gonads are put into urine production ponds, and eco-stimulation methods are used to promote their natural spawning.
2. Incubation cobia fish eggs were round and slightly yellow, floating eggs, eggs of the fertilized eggs slightly water swelling, egg diameter 135 microns to 141 microns. Poor eggs are opaque and poorly buoyant and should be removed. The number of eggs per kilogram is about 500,000. When the water temperature is between 24°C and 26°C, the membrane can be hatched within 30 hours; when the water temperature is 28°C to 30°C, the membrane hatches within about 24 hours.
3. Larval larvae Newly hatched larvae are quite large in size compared to other marine fish. The overall length is about 3.5 mm. The body has melanin distribution. The oil globules are below the yolk sac and the fins are translucent. The fins are suspended at rest. In water, the abdomen faces upwards and is horizontal or inclined. At 12 hours after membrane rupture, the larvae were 4 mm in length and about 4.8 mm in length in 24 hours. The larvae were dark brown in color, with a silvery yellow color beginning from the back of the head to the tail. Occasionally, the larvae rushed for a short and anxious swim. , mainly suspended in water. The third day old larvae had a total length of 6 mm, a mouth width of about 0.4 mm, a large mouth, brown pigmentation around the spine, a dark brown trunk, and a slightly silvery tail. From day 3, that is, 60 to 66 hours after membrane rupture, the larvae started feeding.
The biological characteristics and artificial propagation of cobia
Cobia is also known as the sea clam, which belongs to the genus Cichlid, Coelidae, and Cobia. It is distributed in tropical waters such as the Atlantic Ocean, Indian Ocean and the Pacific Ocean (excluding the East Pacific Ocean). The individual can reach up to 1.5 meters and weigh 43 kg. The world’s major fishing producing countries are Pakistan, the Philippines, and Mexico. China’s coastal areas are also distributed, but their production is low. According to years of research by researchers, cobia is easily domesticated and eats artificial feed. Its growth rate is fast, and its annual weight gain can reach 6 kg to 8 kg. It is one of the fastest-growing and most industrialized fishes in marine cage culture. It is comparable to Norway's main farmed fish, the Atlantic Ocean.