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Artificial reproduction of cobia
Cobia, also known as sea trout, is a tropical fish found in the Atlantic, Indian, and Pacific Oceans, excluding the eastern Pacific. Major fishing regions include Pakistan, the Philippines, and Mexico, while China's coastal areas also host this species, though with lower production. As a carnivorous fish, cobia has delicious meat and is ideal for raw fish fillets. It adapts well to captivity and can be fed artificial feed, growing rapidly—reaching 6 to 8 kg annually. This makes it highly promising for sea cage farming.
**Biological Characteristics**
First, diet: In the wild, smaller cobia mainly eat shrimp, crabs, and cephalopods, making up about 80% of their diet, with fish being secondary. Larger cobia (over 1 meter) primarily consume fish. Under farming conditions, they readily accept pellet feed.
Second, temperature: Cobia thrives in warm waters, with optimal embryonic development between 24°C and 31°C. Juveniles (10–15g) can survive down to 20°C, but feeding decreases below 20°C. At 19°C, they stop eating, and at 16°C, they begin to die. They remain active between 22°C and 34°C, but at 36°C, feeding continues, though mortality increases.
Third, salinity: Cobia is a euryhaline species, surviving between 4‰ and 35‰ salinity. When salinity rises to 40‰, feeding drops by half; at 47‰, only weak feeding occurs. If salinity drops below 5‰, they stop eating and eventually die. Maintaining salinity above 10‰ is recommended for aquaculture.
Fourth, oxygen consumption: At 30°C, 0.5g fry consume 1.08mg O₂ per gram per hour, with lethal levels at 1.7mg/L. At 28°C, consumption is 0.86mg/g/h, with a lethal level of 1.5mg/L. Higher temperatures and larger fish increase oxygen demand.
Fifth, reproduction: During spawning season, females develop distinct black and white stripes and a swollen belly, while males show fewer or no stripes. Maturity occurs around 2 years old, with males over 7kg and females over 8kg. Egg count is about 160,000 per kg, with eggs measuring 125–137μm. Spawning typically occurs between April and October in the Gulf Coast, with peak in February to May in southern Taiwan, at 24–29°C.
**Artificial Propagation**
Zhanjiang Ocean University began artificial breeding in 2000, successfully raising 70,000 fry. By 2001, 2,000 were selected as broodstock, with vitamin and mineral supplements to improve egg quality. In 2002, 360,000 fry were raised.
For spawning, hormones like LRH-A2, HCG, and DOM are used, with two injections. Some broodstock are induced naturally through environmental stimulation. Fertilized eggs are slightly yellow, oval, and floating, with a diameter of 135–141μm. Hatching takes 24–30 hours depending on temperature.
Newly hatched fry measure 3.5mm, with melanin and oil globules. They swim vertically, and by 12 hours, they grow to 4mm. Feeding starts around 60–66 hours post-hatching, beginning with rotifers, then copepods, Artemia, and finally minced fish. Nutrient-enriched feeds, such as chlorella and cod liver oil, boost survival rates.
In earthen ponds, fry are raised similarly to freshwater species. Water is cleared, fertilized, and monitored to ensure sufficient food. Fish are fed when plankton blooms occur. Regular screening ensures uniform growth before transferring to seawater cages. This process helps maintain high survival rates and healthy development.