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).