(1) Feeding and Nutrition: The feed used for raising fry is generally similar to that of other marine fish, including rotifers, Artemia nauplii and adults, and finely minced fish. Copepods and clams are also excellent food sources when available. Fry typically begin feeding around 7 days after hatching. Since they still have a large yolk sac at this stage, feeding should be initiated before the yolk is completely absorbed. Unlike some other species, false eye flounder (Paralichthys olivaceus) swims horizontally from the moment of hatching, so swimming behavior alone isn’t a reliable indicator of when to start feeding. The recommended rotifer density is over 2 per milliliter. Figure 5 shows a feeding schedule for reference: feed rotifers from day 7 to day 21 post-hatching. Starting on day 11, Artemia nauplii can be introduced. By day 27, small amounts of minced fish can be added. At this stage, fry cannot swallow large pieces, but they can consume the entire skeleton of small fish. If conditions allow, larger prey such as adult Artemia or shrimp can be offered during fish feeding. Feed four times daily, with two feedings in the afternoon. In spring and summer, the nursery period is during the day. The first feeding should be done as soon as possible to prevent cannibalism caused by hunger. The last feeding should be done just before dark.
(2) Stocking Density: The density in the nursery is closely related to culture techniques. With sufficient water exchange and adequate food supply, the density can be increased. The numbers mentioned here represent the current general practice. False eye flounder is more prone to cannibalism compared to other species. Newly hatched larvae can be stocked at 5,000–10,000 per cubic meter. When they reach 10–15 mm, the density should be reduced to 1,500–2,000 per cubic meter. At 20–25 mm, it should be around 1,000 per cubic meter. For fry measuring 30–35 mm, the ideal density is 600–800 per cubic meter, and for those 40–50 mm, it should be 400–500 per cubic meter.
(3) Preventing Cannibalism: False eye flounder and similar species are particularly prone to cannibalism. Fry start biting each other when they reach about 4 mm in length, usually targeting the caudal and pectoral fins. While some fry can escape, the damaged fins lead to many malformed individuals above 5 mm. As they grow, the behavior becomes more severe. By the time they reach 40 mm, they may even bite off tails, leading to death. Currently, there is no method that can completely prevent cannibalism, but its occurrence can be reduced. Here are some effective strategies:
1. Separate fry of different sizes into separate ponds. This helps smaller individuals grow better and reduces mortality risk.
2. Provide sufficient food. Hunger increases the likelihood of aggressive behavior. Ensuring adequate feeding reduces biting, though not entirely.
3. Reduce stocking density appropriately. Lower density decreases the chance of aggressive interactions.
4. Trim the teeth of larger fry. This method works best for fry aged around four months. Teeth are attached to the jaw and must be cut rather than pulled. After cutting, they will regrow. Specialized tools like rongeurs are used for this purpose, and the process also helps slow down the aggression.
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