The major farming systems for mandarin fish are pond culture, cage culture and pen culture. Both monoculture and polyculture is carried out in ponds, while cage and pen culture is used in open waters such as reservoirs, lakes and even rivers.
Seed supply
Since natural seed availability has become limited as a result of intensive capture, farmers have had to find a way to enhance the supply by induced breeding.
Brooders are collected and selected from both open waters and farmed fish. They need to be healthy, active, and large; the use of two-three year-old fish at 1-2 kg is normal but 0.5 kg males and 0.75 kg females are also effective for breeding. Extra care is taken to condition broodfish well, from 40-60 days prior to spawning. The hormones used for induced breeding are usually PG, HCG, and LRH-a, either singly or in combination.
Dosages for females are shown in the following table (males only receive half these amounts):
Treatment |
One injection (per kg fish) |
Two injections (per kg fish) |
1st injection |
2nd injection* |
PG |
HCG |
LRH-a |
PG |
LRH-a |
PG |
LRH-a |
Single hormone |
14-16 mg |
– |
– |
0.8-1.6 mg |
– |
10-15 mg |
– |
Combined hormones (I) |
1.5-2 mg |
500-800 IU |
– |
– |
20 µ |
2.5 mg |
200 µ |
Combined hormones (II) |
– |
500 IU |
50 µ |
– |
– |
– |
– |
* The interval between the first and the second injection is about eight hours.
Hatchery production
After being injected the brooders are placed in spawning tanks. Natural spawning or artificial insemination is used. Eggs hatch in 23-30 hours, depending on water temperature and hatching facilities. Careful hatchery management to ensure suitable water flow is essential. Water temperature should be kept relatively stable; at 25-29 °C it takes 20-30 hours for hatching to occur but can take 50-60 hours if temperatures are lower than this range.
Rearing fry
Newly-hatched mandarin fish are only 4 mm and are fragile; after 50-60 hours, body length increases to 5 mm and they start to feed; without feed, cannibalism occurs. Fry are fed at approximately two-three live fish fry per mandarin fish per day at first; silver carp, bighead, grass carp, Wuchang fish or tilapia fry are used. By day four the mandarin fish fry will consume four-five live fish fry per day.
Nursery
The nursery phase may be conducted in flowing or static water.
Flowing water nursery
The stocking rate is 5 000-10 000 fish/m³, depending on hatchling size; 50-100 m³ concrete tanks, which may be square or rectangular, are used. After five-seven days, the fry are transferred and restocked into earthen ponds. Feeding should cease 10-12 hours prior to transfer to prevent physical injuries.
Standing water nursery
Preferably, tank size is 4 x 6 x 0.8 m and the stocking rate is 7 000/m³. Branches are placed on the bottom of the tank to provide shelter for feeding activities.
Pond nursery
Farmers prefer to rear the fry further in static water earthen ponds after they reach 1.5 cm, which takes about 10-15 days in the tanks. The minimal pond size is 1 000 m², with a water depth of 0.5-1 m. The pond is prepared with a sandy, low silt bottom.
After 20-25 days in the nursery pond, the fish reach 3-5 cm in body length; this is the correct time to transfer them into the fingerling rearing facilities. It is important to grade the fish every week; otherwise the fast growing individuals will prey upon smaller fish.
Fingerling production
Many farmers nowadays do not use a separate fingerling production phase, preferring to stock 3-5 cm fish fingerlings directly into the grow-out ponds. However, other farmers do use an intensive fingerling production phase. In these cases, the stocking density is 3-4.5/m² and the feeding rate is 5-10 percent of the standing crop. The fingerlings may be reared either in monoculture or in polyculture with carps, or in cages. Pond farming is the most efficient method; ponds of 2 000-4 000 m² and 1.5 m deep are utilized. Survival rates of 50-70 percent are common but 90 percent is achievable.
Ongrowing techniques
Several farming systems for mandarin fish are used in China; all are very successful in practice.
Pond farming
Pond farming is one of the most popular methods used, either in monoculture or polyculture.
Monoculture is conducted either in earthen ponds or concrete tanks. Earthen ponds are typically 0.7-1.0 ha in area and 2.5 m deep, while the concrete tanks are half that area and 1.5-2.0 m deep. The pond bottom is rather compact and sandy and some branches are usually provided as shelters. Since mandarin fish does not need fertile water, slightly flowing water is best. The average stocking quantity is 50-80/100 m² of 3 cm fingerlings. Sufficient food supply (5-10 percent of biomass) is essential to prevent cannibalism. Feed (new live fish) is provided every five days, roughly about two-three days before all the feed previously supplied would be consumed; this is because the live fish provided as food also grow in the pond and become too large for the mandarin fish to consume.
The polyculture system is also applied in earthen or concrete ponds. The stocking rate is 40-70/100 m² of 3 cm mandarin fry. In this system, there is normally no additional feed supply; the stocking of secondary fish, such as crucian carp and/or tilapia, provides sufficient live feed for the mandarin fish. The stocking density for crucian carp is 1/m² and for tilapia is 30-50/100 m². Fry and fingerlings of silver carp, bighead and grass carp are also good live feeds for mandarin fish, being cheap and readily available resources.
Cage culture
Net cages, placed in unpolluted areas with high dissolved oxygen content, are supported by and fastened to bamboo poles. Cage sizes depend upon the open water space available and the managerial skills of the farmers. Generally they are between 50-100 m² and are placed 50 cm above the lake bottom. Stocking rates are typically 20-40/m² and the feeding regime is similar to that in pond culture.
Pen culture
Pens, situated in the shallow parts of lakes or reservoirs, range in size from 0.2 to 10 ha. Smaller pens are preferred for easy operation and management, but the capital investment per unit is higher. The stocking rate used is 1 500-2 000/ha of 3-5 cm fish. Pen culture is generally extensive; feeding normally depends on the wild fish present in the area but supplemental (live) feed is given if available.
Feed supply
No commercial artificial feeds for mandarin fish are yet available.
Harvesting techniques
Having started to breed when temperatures reach 21 °C (late March or early April in southern China) and taken a further 20-25 days to reach the 3-5 cm stocking size for on-growing, by late November or early December the on-growing facilities are ready for harvesting. By this time mandarin fish will have reached an average of 450-600 g. Pond production can reach 6 750-7 500 kg/ha in monoculture or 3 000-4 500 kg/ha in polyculture. Harvesting is generally done once a year. The fish are netted out when the pond is completely drained; the water level is reduced first, to simplify netting. However, selective harvests are also conducted prior to the final harvest, generally starting in September when the fish first reach a minimal market size. In the cage culture of mandarin fish, harvesting is carried out by lifting the corners of the cages, following which scoop nets are used to catch the fish. Harvesting in pen culture varies and may involve trawling nets, gill nets and traps.
Handling and processing
Unlike the supply of carp, the availability of farmed mandarin fish is limited on a national scale. With such relatively small quantities available, mandarin fish are therefore sold fresh or live; as yet, there is no processing, not even salting.
Fingerling production
Mandarin fish are highly valued and non-traditional. The price of the fish in the market is about 4-10 times higher than the traditional carp; therefore there is currently plenty of opportunity for farmers to make a profit in this industry. However, the costs of the production will certainly rise. Production costs are mostly attributable to feed (live fish, sometimes prawns) which accounts for 40-45 percent; pond rental, chemicals, labour, water and power comprises the rest. Total production costs ranged between USD 2.2-2.8/kg in 2004 and early 2005.