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 weight can reach 6kg to 8kg. It is the most fish breeding prospect in sea cage culture.
Biological characteristics
First, food. In natural sea areas, 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 that is not resistant to low temperatures. After the experiment, the suitable water temperature for embryonic development is between 24°C and 31°C; for the sub-fish stage (body weight 10g~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 to 18°C Weakened, still at the bottom of the water, began to die at 16°C. The water temperature of 22 °C ~ 34 °C has obvious feeding activity, the water temperature rose to 36 °C, although feeding behavior, but it has begun to die.
Third, suitable salt. For wide-salt fish, salinity is evident when the salinity is between 4‰ and 35‰. 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 ‰ there was only a weak feeding behavior; at 47 ‰, it began to die. When the salinity dropped from 30 ‰ to 5 ‰, it did not cause immediate death and there was still feeding behavior. The salinity dropped to 3 以 at a rate of 1 ‰ per day at 5 ‰, 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 ‰ or more.
Fourth, oxygen consumption. After testing, the average body weight of 0.5g fish fry, when the water temperature is 30°C, the oxygen consumption is 1.08mg/gh, the lethal dissolved oxygen amount is 1.7mg/L; when the water temperature is 28°C, the oxygen consumption is 0.86mg/gh, lethal The amount of oxygen is 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 minimum body maturity: In the reproductive season, the black and white stripes on the back of the cobia females will become more pronounced, and the abdomen will be particularly prominent, while the mature males will have no obvious or disappeared stripes and the abdomen will be 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 region is 2 years old. The male fish weighs more than 7 kg and the female weighs more than 8 kg. The relative amount of eggs is about 160,000 for 1kg body weight and about 1.28 million for 8kg fish. The egg size is small, and the egg diameter of the 4th phase egg cell is 125 um-137 um. 2. Spawning season: In the natural sea area, cobia is a spawning fish. It has a long reproductive period. 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°C to 29°C.
Artificial Propagation
Cobia can be cultivated as broodstock under artificial breeding conditions. In 2000, Zhanjiang Ocean University began research on the artificial reproduction of cobia, and succeeded in producing 70,000 to 8 centimeters of 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, the hatching army of cobia eggs slightly yellow oval, floating eggs, fertilized eggs, slightly swelling of the egg membrane, egg diameter 135um ~ 141um. Eggs with poor eggs are opaque and poorly buoyant. The number of eggs per kilogram is about 500,000. When the water temperature was between 24°C and 26°C, the membrane was hatched within 30 hours. When the water temperature was 28°C to 30°C, the membrane hatched in about 24 hours.
Third, the sub-fish to cultivate newly hatched sub-fish compared with other marine fish, the body has been quite large, about 3.5 mm in length. The body has a melanin distribution, the oil globules are below the yolk sac, and the fins are translucent. When the body is stationary, the fish are suspended in water and the abdomen is upwards, horizontally or obliquely. 12 hours after the rupture of the membrane, the fish is 4 mm in length and the total length is about 4.8 mm in 24 hours. The color of the fish is dark brown, and the silver color develops from the back of the head to the tail. The fish is short and acute. The swimming is mainly suspended in water. The third-day-old fish 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 fish started feeding, that is, they started feeding 60 to 66 hours after membrane rupture. After the fishes feed, according to the requirements of nutrient requirements and palatability at different stages of growth and development of the fish, 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 acid (HUFA) required for the growth of sub-fish, improve the survival rate of seedlings, and adopt nutrient-enhanced measures for the biological feed, the high-concentration chlorella and emulsification of rotifers for 6 hours to 8 hours before feeding are performed. Cod liver oil was inoculated again after feeding. Usually 3 days to 10 days of feeding rotifers; 8 days to 15 days of feeding copepods mainly; 10 days to 25 days of feeding Artemia nauplii slowly, adult; 20 days after the start vote Feed the larvae, Artemia, and finally the fish. When the bait is switched, several days are the adaptation process of two different bait crossing feeds. The 18th-day-old fish has an average 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 the full length of 7 Above centimeters, transfer to seawater cage 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 fish can open their mouths for feeding, that is, they can be cultivated to more than 7 cm in time. The key point is that when the fish are feeding, their food feeds coincide with the rush hour of the food in the pond. This ensures that when the fish is feeding, there is enough feed in the water body. 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.
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