(1) Feeding and Rearing: The diet for raising fry is generally similar to that of other marine fish species, including rotifers, Artemia nauplii and adults, as well as small fish. Copepods and clams are also excellent food sources, provided they are of high quality and properly cultured. Larvae typically begin feeding around 7 days after hatching. Although they have a large yolk sac, they start feeding before it is fully absorbed, so feeding should be initiated in advance. Unlike some other fish, the false eye (a type of sea fish) does not go through the same developmental stages as the gums. The latter tends to hang vertically at first and then swim horizontally, while the false eye swims horizontally from the moment of hatching. Therefore, swimming behavior alone cannot be used to determine if feeding should start. The density of rotifers should be more than 2 per millimeter. Figure 5 shows a feeding schedule for reference: feed rotifers from day 7 to day 21 post-hatching. On day 11, Artemia nauplii can be introduced. By day 27, a small amount of minced fish can be added. At this stage, fry cannot swallow large pieces of fish, but they can consume the fine filaments of fish. If possible, larger prey such as adult Artemia or shrimp can be offered when feeding with fish. Feed four times a day, with two feedings in the afternoon. The nursery period usually occurs during spring and summer, and feeding is done during daylight hours. The first feeding should be done as soon as possible to prevent fry from fighting due to hunger. The last feeding should be done just before dark.
(2) Fry Density: The density of fry in the nursery is closely related to culture techniques. A higher water exchange rate allows for increased stocking density, as it ensures sufficient food supply. The numbers mentioned here represent the current general standards for fry rearing. False eye fish tend to exhibit more aggressive behavior compared to other species, making them more prone to cannibalism. Newly hatched larvae can be stocked at 5,000–10,000 per cubic meter. When they reach 10–15 mm in length, the density should be reduced to 1,500–2,000 per cubic meter. At 20–25 mm, 1,000 per cubic meter is ideal. For 30–35 mm fry, 600–800 per cubic meter is appropriate, and for 40–50 mm fry, 400–500 per cubic meter is recommended.
(3) Preventing Cannibalism: False eye fish, along with other species, are known for their aggressive behavior. Fry tend to bite each other once they reach about 4 mm in length, often targeting the caudal and pectoral fins. While some fry can escape, the damage to their fins results in many malformed individuals above 5 mm. As they grow, the aggression increases, and by the time they reach 40 mm, they may even bite off tails, leading to death. Currently, there is no method that completely prevents cannibalism, but its occurrence can be minimized. Here are some effective strategies:
1. Separate fry of different sizes into different ponds. This helps smaller individuals grow faster and reduces mortality risk.
2. Provide adequate feeding. Hunger increases the likelihood of aggressive behavior, so ensuring enough food can reduce biting incidents, although it cannot eliminate them entirely. Some believe that certain fish enjoy biting, as seen in cases where cages were damaged and air tubes were snapped during breeding.
3. Maintain an appropriate stocking density. Lower density reduces the chances of aggression among fry.
4. Consider trimming the teeth of larger fry. This method is suitable for fry aged around four months. The teeth are attached to the jaw and must be cut rather than pulled. After cutting, they will regrow. Tools like rongeurs are commonly used for this purpose, and it also helps slow down the aggressive behavior.
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