Cobia, also known as sea trout, is found in tropical waters such as the Atlantic Ocean, the Indian Ocean, and the Pacific Ocean (except the East Pacific). Pakistan, the Philippines, and Mexico are major fishing producers, and China's coastal areas are also distributed, but production is low. Cobia is a carnivorous fish, and its meat is delicious. It is a good material for raw fish fillets. Cobia is easily domesticated and eats artificial feed. Its growth speed is fast, and its annual growth can reach 6-8 kilograms. It is a kind of fish that has the most breeding prospect in sea cage culture.
Biological characteristics 1. Food In the natural sea area, smaller cobia mainly feed on shrimps, crabs, and cephalopods, accounting for about 80% of the total food, followed by fish. For cobia that is more than 1 meter in length, fish is the dominant type, accounting for 80% of the total food. Under artificial breeding conditions, cobia can be fully domesticated and fed artificial pellet feed.
Second, suitable temperature cobia is a tropical sea fish, intolerant of low temperature. After testing, the suitable water temperature for embryonic development is between 24-31Â°C; at larval stage (body weight 10-15 g), the water temperature is as low as 20-21Â°C, the food intake is significantly reduced, no feeding at 19Â°C, and the activity at 17-18Â°C is weakened. At the bottom, death began at 16Â°C. The water temperature was 22-34Â°C and there was obvious feeding activity. The water temperature rose to 36Â°C. Although there was feeding behavior, it began to die.
Third, salt-tolerance fish is salt-tolerant, and salinity is evident when the salinity is 4â€°-35â€°. The tested salinity was below 35 , and increased at a rate of 1 æ¯æ—¥ per day. When the salinity rose to 40 ,, the feeding was halved; at 43 â€° there was only a weak feeding behavior; at 47 â€°, it began to die. When the salinity dropped from 30 â€° to 5 â€°, it did not cause immediate death and there was still feeding behavior. The salinity dropped to 3 ä»¥ at a rate of 1 â€° per day at 5 â€°, no feeding behavior, and began to die. Prolonged life in ultra-high salinity or ultra-low salinity may result in slow growth or low resistance. Larger cobias are less tolerant of low salinity, and when the salinity is less than 8 ,, there is no feeding activity. When cultivating as food fish, it is advisable to keep the salinity of sea water at 10 â€° or more.
IV. Oxygen consumption After testing, the average body weight of 0.5 g of fry, when the water temperature is 30Â°C, the oxygen consumption is 1.08 mg/gh, the lethal dissolved oxygen amount is 1.7 mg/L; when the water temperature is 28Â°C, the oxygen consumption is 0.86 In milligrams per gram, the lethal dissolved oxygen was 1.5 mg/l. Under normal circumstances, when the water temperature is higher, the amount of oxygen consumed and the amount of lethal dissolved oxygen increase accordingly; the larger the individual, the greater the amount of oxygen consumed.
Fifth, reproductive habits 1, male and female characteristics and maturity of the smallest body: In the reproductive season, cobia female black and white stripes on the back will become more obvious, particularly prominent in the abdomen, and mature male fish stripes are not obvious or disappear, the abdomen smaller. However, judging from the body color alone may not always be accurate. It is still necessary to judge with a body shape. The cobia raised in cages have different sexual maturation ages. The Zhanjiang area is 2 years old. The male fish weighs more than 7 kilograms and the female fish weighs more than 8 kilograms. The relative amount of eggs is about 16,000 tablets in 1 kg weight and about 1.28 million tablets in 8 kg of fish. The egg size is small, and the egg diameter of the 4th phase egg cell is 125-137 micron. 2. Spawning season: In the natural sea area, cobia are spawning fishes for a long period of reproduction. In the North Gulf Coast of the United States on the east coast of the United States, mature broodstock can be found from April to October. In the southern part of Taiwan, the peak of spawning occurred from the end of February to May, and spawning was sparse until October. Suitable spawning temperature is 24-29Â°C.
Artificial breeding cobia can be cultivated as broodstock under artificial breeding conditions. Zhanjiang Ocean University began artificial propagation research on cobia in 2000 and succeeded in producing 70,000 cm long fish. In which 2,000 healthy physiques were selected to be carefully nurtured and kept as broodstock. From November 2001 to early April 2002. Add vitamins and minerals to the feed, strengthen cultivation, promote gonadal development, improve egg quality. In 2002, about 360,000 fry about 7 centimeters were cultivated.
First, artificial oxytocin selection of the abdomen larger, exposed gonad profile of the broodstock into the darker oxytocin. Induction of production uses luteinizing hormone-releasing hormone analogues (LRH-A2), chorionic gonadotropin (HCG) and domoxone (DOM), injected at the base of the pectoral fins of broodstock. In two injections, the first one accounted for 1/3 of the total, and the second time accounted for 2/3 of the total. For some of the abdominal floppy, gonad-conspicuous broodstock into the urine tank, the use of eco-stimulation methods to promote its natural spawning also succeeded.
Second, hatching cobia fish fertilized oval yellow, floating eggs, fertilized eggs, slightly swelling of the egg membrane, egg diameter 135-141 microns. Eggs with poor eggs are opaque and poorly buoyant. The number of eggs per kilogram is about 500,000. When the water temperature is 24-26Â°C, the membrane is hatched within 30 hours, and the membrane is hatched about 24 hours when the water temperature is 28-30Â°C.
Third, larvae to raise newly hatched larvae compared with other marine fish, body size has been considerable, a total length of about 3.5 mm. The body has a melanin distribution, the oil globules are below the yolk sac, and the fins are translucent. The larvae are suspended in water at rest and the abdomen is upwards, horizontally or obliquely. 12 hours after membrane rupture, the larvae have a total length of 4 mm and a total length of about 4.8 mm in 24 hours. The larvae have a dark brown body color and begin to produce a silver-yellow color from the back of the head to the tail. The larvae occasionally make short and swift swimming. , mainly suspended in water. The third day old larvae had a total length of 6.0 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 the 3rd day onwards, the larvae started feeding, that is, 60-66 hours after membrane rupture. After the larvae open their food, according to the requirements of nutritional requirements and palatability at different stages of growth and development of larvae, different types of bait are used in conjunction with cross-feeding. The order of feeding is: rotifers - copepods - Artemia larvae - Artemia, chironomid larvae - minced fish. In order to increase the highly unsaturated fatty acids (HUFAs) needed for larval growth and improve the survival rate of seedlings, nutritional enhancement measures are applied to the biological feeds. The rotifers are fortified with high concentrations of chlorella and emulsified cod liver oil for 6-8 hours before feeding. Breed after feeding. The rotifers are mainly fed on 3-10 days of age; the copepods are mainly fed on 8-15 days; the Artemia nauplii and adults are slowly fed on 10-25 days; and the cradle starts to be fed after 20 days. Larvae, Artemia, and finally minced fish. When the bait is switched, several days are the adaptation process of two different bait crossing feeds. The 18-day-old larvae have an average total length of about 4.3 cm. At this time, individual fish sizes are uneven. To avoid residual food, individual stocks should be selected according to the size of the individual. After every 5 days, they should be screened once until they reach a total length of 7 cm. Above, transfer to sea cages for culture.
The use of earthen ponds to raise fry is also a commonly used method. The cultivation process is the same as that of freshwater fry cultivation. Clear pond, release water, fertilize and promote the growth of food organisms. The hatched larvae can open their mouths to eat, that is, they can be cultivated to more than 7 cm at the proper time. The key point is that when larvae open their mouths, they are synchronized with the peak food life that occurs in the pond, ensuring that there is sufficient food supply in the water when the larvae open their mouths. In addition, the biological feed in the pool needs to be kept sufficiently. Otherwise, mutual food may occur and the survival rate will be reduced.