Detailed Explanation of Key Technical Points for Mandarin Fish Fry and Fingerling Rearing
Mandarin fish fry and fingerling rearing is the foundation of mandarin fish farming. Unlike other freshwater fish, mandarin fish fry and fingerlings cannot be reared by directly feeding commercial feed in ponds or by the method of fertilizing the water. Therefore, the quality of mandarin fish fry and fingerling rearing techniques directly affects the level of mandarin fish farming profitability. Let us now take a look at mandarin fish fry and fingerling rearing techniques!
Rearing Conditions for Mandarin Fish Fry
1. Environmental requirements: The pond should have a sandy bottom with little mud, an area of 2-3 mu, a water depth of more than 1.5 m, convenient drainage and irrigation, clear and non-turbid water quality, no sewage inflow, and a small amount of submerged aquatic plants. For newly dug ponds, the soil quality should be taken into consideration. Acidic ponds and ponds whose water easily becomes turbid are not suitable for rearing mandarin fish.
2. Pond clearing and disinfection: Clear the pond with quicklime on April 5, pile grass fertilizer at the four corners of the pond around April 10 (if the pond bottom is already fertile enough, fertilization may be omitted), and add fresh water to a depth of 0.8-1.0 m to cultivate water quality, so as to cultivate natural food organisms for forage fish.
3. Forage cultivation: Place fish nests (floating bundles) with crucian carp eggs into the pond for hatching. The fry density is generally controlled at about 500,000 per mu. The eggs can be placed in 2-3 batches, with an interval of one day between batches, so that mandarin fish fry of uneven sizes all have suitable prey.
Rearing Methods for Mandarin Fish Fry
Newly hatched fry are soft and delicate, smaller than fry of Chinese carps, with a body length of only about 4 mm. After 50-60 hours of rearing, the body length reaches 4-5 mm, and the average heart rate is 3 beats per second. At this point, the mandarin fish fry begin to feed, entering the summer-fry rearing stage. Since the 1990s, mandarin fish fry rearing techniques have been continuously improved and enhanced, and the rearing methods have become diverse. In production, they are summarized into two methods: flowing-water rearing and still-water rearing. The survival rate of flowing-water fry rearing is higher than that of still-water fry rearing, but the growth rate is slightly slower than in still water.
1. Flowing-water rearing: Flowing-water fry rearing is further divided into two methods: rearing in hatching jars and rearing in circular channels. The operations are basically the same.
(1) Rearing conditions: Hatching jars (circular channels) have the advantages of fresh water quality, large water exchange volume, stable water temperature, small temperature difference, and rich dissolved oxygen, meeting the environmental requirements for mandarin fish fry growth. Most production uses this method, that is, continuing to rear the mandarin fish fry that have hatched in the hatching jar (circular channel) in the original jar (circular channel) with artificially controlled water flow.
(2) Stocking density: In the early stage of fry rearing, the stocking density of mandarin fish fry is generally 5,000-10,000 fish per sq m, gradually decreasing as the individual mandarin fish grows larger.
(3) Rearing method: During the mandarin fish fry rearing process, about every 5 days, the fry should be graded by size and transferred to another hatching jar (circular channel) once, and at the same time, the sediment on both sides of the bottom of the hatching jar (circular channel) should be removed. Mandarin fish fry are voracious eaters, so it is best to stop feeding forage fish several hours before transferring from the hatching jar (circular channel) to the circular channel, to avoid unnecessary losses caused by overeating of mandarin fish fry.
2. Still-water fry rearing: Still-water fry rearing is further divided into rearing in fish ponds, cement pools, and net cages.
(1) Rearing conditions: For ponds used to rear mandarin fish fry, cement pools are generally preferred, with an area of 30-50 sq m and a water depth maintained at 0.8-1 m. Artificial reefs simulating natural waters can be placed at the bottom of the pool to create a good predation environment for mandarin fish fry.
(2) Disinfection and stocking: Before stocking fry, the rearing pool must be thoroughly cleaned and disinfected. The stocking density is generally about 7,000 mandarin fish fry per cubic meter of water. When the mandarin fish grow to about 1.5 cm, transferring them to net cages for rearing will produce better results.
Feeding of Forage for Mandarin Fish Fry
Mandarin fish are typical carnivorous fish. They begin eating live fish fry upon opening their mouths, and they cannibalize each other when hungry. This is determined by their biological characteristics. Therefore, accurately grasping the time when mandarin fish fry start feeding, selecting good forage fish, and timely supplying suitable prey are key measures for the success or failure of mandarin fish fry rearing.
1. Time of first feeding: The organ differentiation and development of mandarin fish fry are closely related to water temperature. Under normal circumstances, when the water temperature is 23.5-25 degrees C, 24-26.5 degrees C, and 26-29 degrees C, the intervals from fertilized egg to first feeding of mandarin fish fry are 112-120 hours, 105-115 hours, and 90-98 hours, respectively. At this time, the mandarin fish fry are active in movement and can actively feed.
2. First feeding prey: Whether the size of the first feeding forage fish fry is suitable directly affects the feeding and survival rate of mandarin fish fry.
(1) Selection of first feeding prey: In production, it is advisable to select fry of bream, Wuchang bream, and yellowtail xenocypris, which have a flat and elongated body shape and weaker swimming ability, as first feeding prey. Newly hatched live fry at 8 hours after hatching are especially the best, as forage fish at this time are easily swallowed whole by mandarin fish.
(2) Do not feed old fry: If old fry are fed, mandarin fish fry can only use a small part of the tail of the forage fish, and the remaining part often hangs at the edge of the mandarin fish fry's mouth, which not only affects movement but also easily rots and decomposes in the water, deteriorating water quality and even causing outbreaks of fish diseases.
(3) Feed on time: If suitable forage fish are not available within 3-5 days after the mandarin fish fry start feeding, their activity ability drops sharply, their senses become dull, and they gradually become emaciated and die. They may even cannibalize each other and become stuck and die because they cannot swallow their prey.
3. Forage production: The mouth gape of mandarin fish and the body height of forage fish continuously change with growth. Mandarin fish at different stages need to be fed forage fish fry at a certain developmental stage in order to be swallowed by the mandarin fish.
(1) Mandarin fish fry at 60 hours of age can only swallow fine-scaled xenocypris fry at 60-216 hours of age.
(2) Mandarin fish fry at 84 hours of age can swallow Wuchang bream fry at 60-216 hours of age.
(3) Mandarin fish fry at 108 hours of age can swallow xenocypris and bream fry at all stages before 216 hours of age, and can also swallow grass carp fry at 36-108 hours of age.
(4) Mandarin fish at 144 hours of age can swallow grass carp fry at 36-108 hours of age.
(5) Mandarin fish at 144 hours of age can swallow xenocypris, bream, grass carp, Feng carp, and common carp before 216 hours of age, as well as silver carp at 12-216 hours of age and bighead carp fry at 24-108 hours of age.
4. Feeding quantity
(1) Feeding quantity at different days of age: The daily ration and suitable forage fish size differ for mandarin fish fry and fingerlings of different days of age. For each mandarin fish fry in the initial feeding stage, the daily ration within 2 days is 2-3 fish and feeding is slow; at 2-4 days of age, the daily ration is 4-5 fish; at 5-8 days of age, the daily ration is 8-12 fish; at 8-12 days of age, the daily ration is 10-16 fish; at 14-15 days of age, the daily ration is 15-20 fish. The feeding speed accelerates as the fish grows.
(2) Judging whether forage is sufficient: Well-fed mandarin fish fry have a swollen abdomen that is prismatic in shape, with the caudal peduncle slightly arched. Under flowing-water conditions, they rest motionless against the inner wall or drift with the water. Hungry mandarin fish fry have flat bodies and spread out within the circular channel searching for food. Based on this, it can be determined whether the forage fish are sufficient.
5. Feeding behavior: During the rearing of mandarin fish summer fry, it can be clearly seen that mandarin fish begin swallowing forage fish from the tail. Often, half a fish is held in the mouth while the other half is exposed outside the mouth, and they eat while swimming and digesting, finally spitting out the fish head. Sometimes the head of the forage fish can be seen hanging on the spines behind the gill cover of the mandarin fish larva, and this is often mistaken for a parasite. At this time, note that no medication treatment is needed in this situation; the fish head will fall off naturally after some time.
6. Strengthen management: During the mandarin fish fry rearing period, meticulous management must be implemented. Thoroughly disinfect the water body to prevent pathogens from being introduced into the rearing pond. Strictly control water quality, promptly remove dirt and clean pollution, and timely propagate forage fish, paying attention to matching the needs of mandarin fish fry rearing. Forage fish must be strictly disinfected before feeding. Regularly splash medication into the rearing pond, effectively carry out fish disease prevention and treatment work, and thereby effectively increase the survival rate of mandarin fish fry.