Aquaculture Feed and Fertilizer Resources Information System

Natural food and feeding habits

Mandarin fish consumes live foods at all life stages. Feeding depends largely upon the visual and auditory stimulations produced by moving objects; non-moving food may be rejected (Liang, 1994). Under controlled conditions in confinement or in small waterbodies, the ability of live food to escape is reduced and visual detection is increased, thus enhancing predation by mandarin fish. The susceptibility of potential prey items to mandarin fish is determined by their height, which is related to the size (height) of the oral opening of mandarin fish. Therefore in the selection and preparation of live foods, the size must be considered. Newly hatched mandarin fish fry attack live fish from the tail end, but after 10 d of feeding, visual capacity is developed, and live food is consumed starting with the head. Fingerling and grow-out size mandarin fish always attack the prey suddenly, promptly adjusting to an appropriate position and direction of attack. The first bite is on the head and the following step is to swallow the prey whole (Liang, 1994).  Dead food is immediately regurgitated.

Common live foods for mandarin fish include mud carp (Cirrhinus molitorella), Wuchang fish (also called Chinese bream, Megalobrama amblycephala), silver carp (Hypophthalmichthys molitrix), bighead carp (H. nobilis), grass carp (Ctenopharyngodon idellus), crucian carp (Carassius carassius), common carp (Cyprinus carpio), stone moroko (Pseudorasbora parva) and other wild and trash fish. Wuchang fish fry is preferred at the start of food intake, then feeding bighead and silver carp follows. When body length reaches 25 cm, common and crucian carps are fed.

When the fry of mandarin fish reach 3–4 d post-hatching, they are fed on small fishes; however, should food deficiency occur, the fish will attack its own siblings. At the fry stage, mandarin fish can consume the same size fry of other fishes. In open waters, fingerlings of 10–16 cm are fed on shrimp and other smaller aquatic animals; at 25 cm, it is mainly fed with other fishes. When a variety of prey is abundant, mandarin fish prefers prey of one third its own size and having an elongated form and soft body features. In the grow-out stage, mandarin fish can swallow live foods of a size up to 60 percent of its own length, but a size of 30–40 percent is optimal. The culture of mandarin fish is highly constrained by the availability of appropriate livefood sources. The farmers use live foodfishes farmed in other fish ponds, while some farm practices include the stocking of tilapia as live foods, either in the same water body or in a separated section created by using fish nets, the offspring being directly consumed by mandarin fish.

Feeding behaviour

Trophic level
In the natural environment, grow-out size mandarin fish normally inhabit standing or slightly flowing aquatic systems, particularly favouring densely grown grass areas with open and clean water. At 3–4 d post-hatch, when 50 percent of the yolk sac remains, hatchlings switch to external nutritional sources. The only suitable weaning food is live fish of body size smaller than that of mandarin fish fry; no feeding on plankton or concentrates (formulated feeds) occurs. Table 1 shows the various livefood sources used by farmed mandarin fish at various sizes. Under controlled conditions, each mandarin fish fry consumes two to three other fish fry on a daily basis. Under conditions of food deficit, mandarin fry will become cannibalistic or will attack other fish fry larger than its own body size. Table 2 shows the food compositions for mandarin fish.

Mandarin fish has a strict preference for live foods, both with regard to size and type. In cage culture practice, mandarin fish averaging 9.7 cm in length are fed with Pseudorasbora parva of 6 to 8 cm in length. Initially mandarin fish consumes only the smaller-sized fish, but only when these are no longer available; it turns to the larger individuals. If the smaller fish are again provided, it will return to feeding on them. Mandarin fish can reach a length of 1.3–1.5 cm at 18 d post-hatching and 2.6–3.5 cm in 26 d. At a body length of 1.7–3 cm, the best size for live food is 1–2 cm in length. Table 3 shows the consumption of various live foods for mandarin fish at different size groups. From the tables, it can be seen that the farming of mandarin fish should be closely paralleled with live food preparation. In this regard, there are two key points. Firstly, during the early stages of culture, the live food should be of a size that is highly acceptable to mandarin fish, otherwise it is unfit for consumption, causing blockage of the throat. Secondly, the food source should be prepared prior to the stocking of live foods. The weaning food for mandarin fish is the rotifer. Two strategies are applied: one is the application of animal wastes or composts as base manure at a rate of about 0.2–0.4 kg/m2 at 5–7 d prior to stocking the live foods larvae; the other is to apply green grass for composting at a rate of about 0.3–0.4 kg/m2 at 7–10 d prior to stocking. These basal applications should be supplemented with commercial feeds such as soybean cake or rice dregs to improve the growth rate of mandarin fish.

The feeding behaviour of mandarin fish varies depending on the season, available light, etc. It normally hides itself in dark and densely grown grassy areas or the narrow spaces between stones and bricks, attacking suddenly when prey appears. The fish does not actively feed during the winter, sheltering in burrows or deep water. When spring arrives and the water temperature rises to 18 oC, the mandarin fish moves to shallow water for feeding. Feeding is less active in the daytime than at night. There are two periods of active feeding in a day: 51–57 percent of feeding occurs at dusk and 19–25 percent at dawn; only 10 percent of food consumption occurs between the hours of 08:00 and 18:00.  Seasonally, the most intensive feeding occurs during the months of June and July. Brooders have less appetite than other stages.

Digestive system
At the pre-larval stage, the mouth is already developed and has a horizontal length reaching 0.7 mm, but the teeth are not yet visible. The eyeball is developed with good orbital size, which is essential for future predation. At 5–12 mm (at 5-10 d of age), the fry is active, being able to swim horizontally, while at 3–4 mm in length (2–3 d of age), it can only swim vertically. Upon further development, the mouth circumference is about 1.4 mm. The maximum mouth opening is about 10–15 percent of the body length; therefore, the body height of prey is a key factor in determining food “palatability”. The mandarin fish can consume prey of height ranging from 20 to 90 percent of its mouth height (see Figures 2 and 3).


Figure 2. Frontal view of the mouth of mandarin fish. (Source: 2A, Wu, 1987; 2B, photo by the author)
Figure 3. Lateral view of the mouth of mandarin fish. A (after Wu, 1987), B (photo by author)

Mandarin fish does not have a clear separation between the mouth and the pharyngeal cavity, these being closely connected and termed the buccopharyngeal cavity. This structure is not yet developed in day-old hatchlings, but at two days old, the oral fissures are slightly visible, although the mouth is not yet able to open. At four days old, the buccopharyngeal cavity is developed as three to four layers of epithelia with a small number of taste buds and mucus cells. In younger stages, the upper jaw is longer than the lower; however, at eight days old, the upper is shorter than the lower, as the capacity for predation is developed (Wu et al., 2007).

In five-day-old fish, the teeth have begun to develop, 3 and 4 teeth appearing on the upper and lower jaws, respectively (Wu et al., 2007). At a body length of 9.3 mm (i.e. at approximately 10 days old), the teeth on each jaw have  increased to 20 in number, while at 32 mm body length (at 20–25 days old), there are 30–40 teeth of various size on each side pointing backward as inverted hooks. At this time, the gill arches (five on each side) are well developed, as are the gill rakers (Figure 4). The gill rakers are densely paved with tiny thorns; even though they do have a filtering process, they are highly effective in attacking and tearing live foods. All the gill arches have comb-like teeth. At this time the general feeding organs are well developed for food intake.

Mandarin fish has a strong stomach with a wide superficial area and a number of folds. At the posterior ending of the stomach, there are numerous pyloric caeca (Figure 5). The musculature of the stomach is well developed, providing a strong impetus during food digestion. The structure of the pyloric caeca is similar to that of the intestine, and they compensate for the short intestine (40–50 percent of the body length) by enhancing digestion. The short intestine and “Y”-type stomach of the mandarin fish account for 68 percent of the length of the digestive track and 1.2 percent of the body weight. The wall of the stomach is thick and well supplied with digestive glands; the pyloric caeca number 198–440.

Natural food
At the larval stage, most fishes start feeding on plankton; however, mandarin fish consistently rejects this food. As soon as the yolk starts to diminish, the food intake is live fishes. If the larva is able to take in one live food item, it will successfully survive, if not, it will become weak and slowly die. That is why mandarin fish has poor survival at this critical period at the start of food intake when live food of a proper size is essential. Under controlled conditions, live food preparation should occur only one day later than mandarin fish spawning. Field results show that to enable sufficient consumption, the quantity of live food provided should be 15 times greater than the number of mandarin fish hatchlings. Initially, consumption is small, only 1–2 pieces of live food being consumed; however, 4–5 days later, consumption reaches 5–6 pieces. As the fish reaches 2 cm in length, it has a higher sensitivity to live foods and a strong attack response. At this size, live foods should be available at a density of 750 pieces/m2. The fry used as live food should be replaced every other day, so that the mandarin fish will continuously have an optimal size of live food. Normally fish of 2 cm length should be supplied with 1.2 cm live food. As fish at this stage already display similar feeding habits to those shown by adults, different sizes of mandarin fish should be supplied with the optimal size of live food (Table 4). In the practical operation of mandarin fish ponds, tilapia can be stocked for live food production at 3–5 pairs per 10 m2 (Lin, 1987). In general, the production of each 500 g of mandarin fish will require 2.5–3 kg of live food (Wang, 2004).