Artificial propagation method of cobia

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1. Select broodstock with a large abdomen and visible gonad outlines for artificial oxytocin administration. Ovulation is induced using luteinizing hormone-releasing hormone analogues (LRH-A2), human chorionic gonadotropin (HCG), and domoxone (DOM). These hormones are administered in two injections into the base of the pectoral fin, with the first dose accounting for 1/3 of the total volume and the second for 2/3. Broodstock with loose bellies and clearly visible gonads are placed in spawning ponds and subjected to eco-stimulation techniques to encourage natural spawning. 2. Cobia fish eggs are round, slightly yellow, and buoyant. Fertilized eggs appear slightly swollen, with an average diameter ranging from 135 to 141 microns. Unfertilized or poor-quality eggs are opaque and do not float well, so they should be removed. Approximately 500,000 eggs are present per kilogram. Under water temperatures between 24°C and 26°C, hatching occurs within 30 hours, while at 28°C to 30°C, hatching takes about 24 hours. 3. Newly hatched larvae are relatively large compared to other marine fish species, measuring around 3.5 mm in length. The body shows melanin distribution, and oil globules are located beneath the yolk sac. Their fins are transparent and remain suspended when at rest. In the water, the larvae typically float with their belly facing upward, maintaining a horizontal or slightly inclined position. By 12 hours after hatching, the larvae grow to about 4 mm, reaching 4.8 mm by 24 hours. They are dark brown in color, with a silvery yellow hue starting from the head to the tail. Occasionally, the larvae exhibit short, anxious bursts of movement, but they primarily remain suspended in the water column. On the third day, the larvae measure approximately 6 mm in length, with a mouth width of about 0.4 mm, a wide mouth, and brown pigmentation along the spine. Their trunk is dark brown, and their tail has a slight silvery tint. Feeding begins on day 3, around 60 to 66 hours post-hatching.

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