Live foods
As stated above, mandarin fish depends completely upon live foods, regurgitation occurring when the food is not alive. There are a number of approaches to live food production, as well as a variety of live food species:
Independent culture
In this system, live foods are cultured separately in different ponds; the supplies prepared normally being three times greater than the demand. As clarified earlier, three-day-old mandarin fish hatchlings with absorption of the yolk sac and reaching 4–4.5 mm in length start to consume live foods, beginning with two-day-old Chinese bream. Due to the limited fecundity of the Chinese bream, breeding of grass carp is also conducted; however, it is important to mention that in order to ensure the availability of appropriate-sized live food, the hatching of grass carp should be well coordinated with the demands of the mandarin fish. The number of grass carp hatchlings to be prepared should be at least 50 times that of the number of mandarin fish being cultured: the first supply of grass carp should be three times greater than the standing crop of mandarin fish; feeding is done three to four times per day. It is worthwhile to remember that grass carp with pigmentation should be supplied to the 8 to 10-day-old mandarin fish, the daily feeding quantity being 8–10 times, with feeding occurring 2–3 times per day. Spawning of grass carp should be conducted three times after the mandarin fish have consumed food for 2–3 d. This live food is maintained in the hatchery ready for 10-day-old mandarin fish.
Ten-day old mandarin fish reaching 1 cm in body length can be stocked in small stillwater ponds. At 2 cm, the fish are transferred to a bigger earthen pond. Crucian carp (Carassius carassius) fry is also a palatable live food for mandarin fish. The breeding and rearing of crucian carp should begin In late April as the water temperature reaches 16–180C, prior to the stocking of mandarin fish. In one week, live foods are collected every 3 d to feed mandarin fish. The feeding of crucian carp should be limited in case its fast growth makes it unfit for consumption by mandarin fish. The supply of live food should be 10 times greater in the mandarin fish pond. Mandarin fish will reach 6–8 cm by the end of May, when it is time for intensive farming of the grow-out stage. At this stage, live food production should be sufficient to satisfy the growth of the cultured fish; normally the area used for live food production is three to four times greater that that used for mandarin fish culture.
Live food production should involve the use of an area of a 0.25–0.5 ha with an abundant water supply. The pond should be limed at the rate of 3–4 kg/10 m2, with the addition of organic wastes at 3 kg or so per 10 m2. The supply of 1 000 crucian carp fry or 800 silver carp fry per m2 as live food is preferred. The managerial routine is the same as with the conventional farming practices (Zhang and Shi, 2006). The fish ponds used for live food production can be used for a number of croppings, a certain number of marketable-size fish and prawns being cultured at other times.
Concurrent culture
This approach is quite efficient in making use of the fish pond as a dimensional system. The fish and the live food are cultured simultaneously in the same confinement. The cultured fish stocked in early May at a size of 3–4 cm can reach 400 g each by mid-September of the same year, while production can reach 3 000–4 500 kg/ha (Wang, 2007). The detailed operating procedures are as follows:
- Pond preparation: The fish pond preferably ranges between 1 350 and 3 350 m2 in size and is rectangular in shape with a water depth of 1.5 m. Fish sumps are used for collecting the grow-out fish as a final product. The sumps are prepared in a form of a 十, 井 or 口 at the pond bottom. The sump ranges between 0.6 and 1 m in width and from 0.5 to 0.7 m in depth.
- Stocking of the live foods: A high density of live foods leads to vulnerability to oxygen depletion, while a low density cannot meet the food supply needs. According to field practice, live foods should be at a density of 3 800–4 500 fish per m2. Moreover, the size of the live food should be well controlled to keep pace with the growth rate of the cultured fish. In order to provide an appropriate quantity of live food, provision procedures are suggested as: 1 to 4 days after pond fertilization, silver carp and bighead carp hatchlings are stocked as live foods at 1 500 per m2; one week later, the same quantity is again stocked; and again an additional week later, stocking of the same number is performed. The third stocking should be accompanied by the stocking of mandarin fish of size 3–4 cm at an average rate of 1 fish per m2. After the stocking of the cultured fish, the concentrates are applied to the pond is within 20 d at a frequency of 4–6 times per day to ensure growth of the live foods (Yang, 2006). At this point, supplying live foods of appropriate size and quantity is vitally important. Mandarin fish has a strong resistance against diseases, but at the larval stage it is vulnerable to the attacks of fish lice and protozoans (Trichodina, Ichthyophthirius and Chilodonella). At the grow-out stage, mandarin fish is vulnerable to gill-rot and enteritis.
Formulated feed
Although there have been some reports on the trial formulated feeds, the results have not been satisfactory and the performance is not promising (Liang et al., 1999). However, there are also some trial results at the laboratory scale (Wu and Li, 1989; Ziang, 2007).
In the tests previously mentioned, it was found that young fish (average weight of 15.9 g) require a protein content in formulated feeds of 44.7–45.8 percent. For grow out, the feed protein content is quite high, and there is good acceptability for fat content and poor or little use of saccharides (or starchy food). The studies show that for a feeding rate of 5 percent for young fish, the protein content should be 53 percent and the fat content 6 percent, while at a feeding rate of 3 percent for grow out, the protein content should be 47 percent and the fat content 12 percent.
Artificial feed demands a quality protein in its formulation. As a key ingredient, fishmeal should be fresh, with no substitutes, otherwise, the fish will become anorexic, leading to high waste of the commercial feeds. Of course there are additional ingredients needed in feed formulation, including addition of less than 20 percent shrimp meal and 10 percent of yeast meal or maize protein. The fat should be a fresh animal oil (such as chicken oil) and cod-liver oil mixture. The baseline should be 5 percent in the feed formulation. Due to the poor use of saccharides by mandarin fish, the addition of α-starch should be at less than 5 percent. Information on the vitamin requirements of mandarin fish is lacking. However formulated feeds for channel catfish and salmon (including vitamin compositions) are sufficient to meet the requirements of mandarin fish under laboratory conditions. Tests have also shown that the texture (softness) and other physical characteristics of the artificial feeds are also of great concern in the feed intake process. During artificial feed preparation, ingredients are finely ground using 80 µm mesh. Fishmeal is mixed at the rate of 40 percent, baseline at 14 percent; for binding, carboxy methyl cellulose is employed; the moisture content is 30 percent. The feed form suggested is the long type, (a ratio of 2:1 or 3:1 is optimal), while the feed colour should be white or light-grey, but not dark. The feed formulations for both juvenile and grow-out stages are listed in Table 8 and Table 9, respectively.
There are some other reports on protein analysis (Wu et al., 1995). Tests were made on eight groups, with six groups being given protein levels ranging from 38.2–49.9 percent; while group 1 was without protein, and group 8 was fed on live fish. The tested fish grouped at random averaged 15.9±2.2 g in body weight. The fish belonging to groups 2–6 were force-fed with the concentrates (formulated feed) for 1 week prior to the beginning of the test, which lasted for 30 d. The formulated feeds prepared for mandarin fish are quite comprehensive, the protein source not being restricted to one or two sources. The feed ingredients are listed in Table 10. The growth performance and the final weight are listed in Table 11. The test results show that higher protein content results in better growth performance, the tested gradients are between 38.2-49.9 percent, the best result was from the 43.6 percent, 46 percent and 48.6 percent protein level, at this level, the net body increment reached 18 g, 15.3 g and 16.2 g respectively, while the FCR for the three group was 1.57, 1.62 and 1.95 which were all lower than the rest. Therefore it is agreed that the best range of the formulated feeds are suggested at this range. Meanwhile due to the predating characters of mandarin fish, the fish should be avoided with rough and mishandlings or injuries and disease attack possibly occurred. The tests were suggested and conducted at the fingerling size, which is much easier for food training than is grow-out size fish.
In general, the development of artificial feeds for mandarin fish has not been successful, even though efforts by both researchers and farmers have been made. Some tests have tried to train the fish on to quality artificial feeds; however, the success was quite limited.
