Southern catfish, also known as southern pupal fish, are native to the Atlantic coast from North Carolina down to North Florida, as well as along the southern coast of Texas. These fish migrate to the sea in the fall from estuaries or coastal areas. Depending on temperature and gonadal development, they can begin spawning as early as December, with spawning typically occurring from late January to February. After spawning, they return to rivers or brackish water environments where their larvae feed on zooplankton near the coast. The larvae undergo metamorphosis after approximately 60 days.
The southern catfish is a highly regarded species worldwide, known for its wide temperature tolerance, rapid growth, and large habitat range. It can thrive in both seawater and freshwater environments and is more resilient to extreme temperatures than some other fish species like the gudgeon.
Successful seedling rearing technology in the southern region involves several critical steps. These include algae inoculation, green water cultivation, intensive rotifer and alfalfa culture, temperature and light control, bait transition, gender management during metamorphosis, and albinism prevention. Here’s an overview of the key techniques used in southern fish seedling cultivation:
1. Prepare a hatchery room equipped for incubation, ensuring regular disinfection of the water. Maintain a water temperature between 17°C and 21°C, with salinity ranging from 18‰ to 35‰.
2. Cultivate Chlorella in seawater using sand filtration and bleaching powder sterilization. Apply fertilizers such as ammonium sulfate (100g/m³), superphosphate (15–30g/m³), and urea (10–30g/m³). Inoculate the culture and use fluorescent lights at night to enhance light exposure. Keep the temperature around 20°C. The Chlorella concentration should be maintained at 2,000 to 2,500 cells/mL, serving as food for rotifers.
3. The egg density in hatching tanks depends on the water conditions, usually around 250,000 to 350,000 eggs per cubic meter. Micro-inflation is used to maintain oxygen levels. Under optimal conditions, hatching takes about 3 to 5 days.
4. Early-stage larvae (5–20 days) are fed S-type to L-type Chlorella. Maintain a Chlorella density of 5–10 cells/mL. Regularly add Chlorella liquid to keep the concentration between 100,000 and 300,000 cells/mL. Before introducing rotifers, increase the Chlorella concentration to 2,500 cells/mL over 6 hours to enrich the rotifers with ω3 HUFA.
5. During the larval rearing phase (20–45 days), introduce fortified Artemia nauplii at a density of 2–8/mL. At this stage, metamorphosis is nearly complete, and the fish begin to adopt a benthic lifestyle. To increase the female ratio, maintain a temperature of 21°C and moderate stocking density.
6. As juveniles grow, gradually transition from rotifers to Artemia nauplii. The Artemia should be orange in color, with particle sizes between 250μm and 500μm. This bait transition usually occurs within 2–3 weeks, and the fish reach a length of about 2.5cm.
7. When juveniles reach 2.5cm in length, they are sorted and moved to juvenile fish culture tanks. Introduce copepods at a dose of 0.5–2/mL. A balanced diet including multi-dimensional nutrients, fish oil, and high-protein feeds (50%–55% protein, 6%–14% fat) supports healthy growth.
All these stages require clean water, proper aeration, and disease prevention measures. Water changes should be done daily, and aeration should increase as the fish grow. Maintaining stable environmental conditions is essential for successful breeding and healthy development.
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