Mandarin Fish Farming Methods and Key Points of Disease Prevention and Control Technology

Mandarin fish, also known as the Chinese perch, is a valuable freshwater fish species. In recent years, mandarin fish farming has developed rapidly, playing an important role in increasing fishery efficiency and fishermen's income. So how do you farm mandarin fish? What are the key points of disease prevention and control technology?

1. How to farm mandarin fish?

1. Setting up hatching raceways

A raceway is a special body of water that simulates natural ecological conditions, keeping the fish eggs constantly tumbling. Using raceways directly to rear fry provides the living environment required by mandarin fish fry, and more importantly, when the fry begin to feed, they are given palatable prey fish——other live fry that have recently hatched from their membranes. This not only meets the nutritional needs for the growth and development of mandarin fish fry, but also maintains fresh water quality.

2. Selection of broodstock

In China, there are 9 varieties of mandarin fish, including the spotted mandarin fish, the big-eyed mandarin fish, the topmouth culter-like mandarin fish, and the slender mandarin fish. Among them, three have farming value: the spotted mandarin fish, the big-eyed mandarin fish, and the topmouth culter-like mandarin fish.

Mandarin fish prefer flowing water for spawning. For artificial breeding, first select healthy, uninjured broodstock weighing 1-2 kg and raise them in a dedicated pond. When feeding them wild trash fish or commercial feed, artificial induced spawning can be carried out by injecting hormones such as carp pituitary, HCG, or LRH—A, allowing them to spawn naturally.

3. Fry rearing in net cages

Mandarin fish eggs are slightly sticky and have a higher specific gravity than water, so they tend to sink to the bottom. When hatching in raceways, the flow rate should be increased and must not be less than 0.2 m per second. After 3-4 days, the fertilized eggs hatch into fry. Artificial insemination can yield more fry. Naturally occurring fry can also be collected for farming.

Net cages are an ideal place for rearing mandarin fish fry. They ensure a sufficient and readily available supply of prey, while fresher water is continuously exchanged through them. The downside is that recently hatched prey fish cannot be fed, the cages need frequent washing, the net cages must be replaced regularly, and fry management is rather cumbersome and difficult to operate.

Net cages generally adopt a three-stage fry-rearing method:

Stage I cages: open-topped cages sewn from 40-28 mesh/3 cm ethylene netting, 4-6 m long, 1 m wide, and 1 m deep.

Stage II cages: open-topped cages sewn from warp-knitted ethylene netting with a mesh size of 0.3 cm, 2 m long, 1 m wide, and 1 m deep.

Stage III cages: open-topped cages sewn from warp-knitted ethylene netting with a mesh size of 0.5 cm, 2 m long, 1 m wide, and 1 m deep.

The matching area ratio of Stage I, II, and III net cages is 1:10:20.

4. Daily feeding

In the early stage, the supporting prey fish are mainly naturally bred allogynogenetic silver crucian carp (Carassius auratus gibelio); in the middle and later stages, the supporting prey fish are mainly farmed Cirrhinus mrigala. The matching area ratio is 1:3.

2. Key points of disease prevention and control in mandarin fish farming

1. White spot disease

The cause is parasitism by Ichthyophthirius multifiliis. The specific symptoms are that when large numbers of the parasite infest the fish body, white spots appear one by one on the fins and body surface of the diseased fish. Because the infected fish is irritated, the body surface and gills secrete large amounts of mucus, and the fish dies from breathing difficulty.

Prevention and control methods:

(1) Soak the fingerlings in 150 mL/m3 formalin for 10-15 minutes;

(2) Splash formalin over the pond at a concentration of 15-25 mL/m3. During treatment, fully oxygenate the water, and immediately after treatment replace it with clean water and oxygenate. Note that copper sulfate or table salt must never be used to treat white spot disease, because these agents not only fail to kill Ichthyophthirius multifiliis, but instead cause it to form cysts and thus multiply in large numbers, worsening the condition.

2. Dactylogyrus disease

It is caused by parasitism by Dactylogyrus. The specific symptoms are that affected mandarin fish swim slowly at the surface, the body color darkens, the gills become noticeably swollen, the opercula open, and the gill filaments turn pale red with abundant mucus. In severe cases, it is complicated by bacterial gill rot. This disease is more serious in summer and autumn.

Prevention and control methods:

Splash strong insecticide at 0.15 g/m2 over the whole pond, apply it again the next day, then add 20 cm of fresh water, and splash bleaching powder at 0.75 g/m2 over the whole pond to prevent and control gill rot caused by damage from the parasites. The effect is relatively good.

3. Key points of prevention and control

(1) Before stocking fingerlings, disinfection work must be done well.

(2) Stock fingerlings that are robust in constitution, uniform in size, lively in swimming, and free of disease and injury.

(3) Feed fresh, high-quality prey.