CATDOLL : CATDOLL: Could you please tell me in detail about the breeding methods of whitebait and Yangtze River knife fish?

Whitebait is a group of small, white and transparent precious economic fish that live in the middle and upper layers of water bodies. It is characterized by wide adaptability, strong reproductive capacity, short food chain, high economic value, tender and delicious meat, and rich nutrition. There are four types of whitebait in our province: big whitebait, Yangtze River whitebait, Taihu new whitebait and oligodont new whitebait. Among them, big whitebait and Taihu new whitebait have higher population yields and have become the objects of fish resource proliferation in large and medium-sized water bodies. The morphological characteristics and living habits of these two fish are introduced as follows.

1. Whitebait

1. Morphological characteristics: Long body, wide and flat head, triangular shape. Pointed and flat snout, large and terminal mouth, mouth cleft extending to below the front edge of the eye. Maxilla extends to below the middle of the eye. Lower jaw slightly protrudes from upper jaw. Tongue is large, with two rows of teeth on it. The origin of dorsal fin is equal to the base of pectoral fin and caudal fin.

2. Age and growth The life span of this fish is 1 year, and the parents die one after another after giving birth. The young fish grow rapidly, reaching the catch size (4 cm) after 2 months, and reaching a body length of more than 10 cm after half a year.

3. Food habits: Silverfish are carnivorous fish. Juvenile fish mainly feed on zooplankton cladopods and copepods. After 7.1 cm, they mainly feed on small fish, and still eat some zooplankton. From 8.1 cm, they become carnivorous fish, mainly feeding on small fish and shrimps such as white shrimp and anchovy.

4. Reproduction The body length of the reproductive group of big silver fish is generally 11 cm to 15 cm. The spawning period is from early January to mid-March, and the water temperature is 2℃-8℃. When the wind is calm, the weather is sunny and warm, and the temperature is above zero, the spawning activity is most active in the hidden water surface and lake bays. The eggs produced are sinking and have sticky threads. The incubation period is about 35 days when the water temperature is between 2℃-10℃.

2. Taihu New Silverfish

1. Morphological characteristics: The body is slender, the head is small and slightly flat, the snout is short and blunt, the mouth is small and terminal, and the mouth cleft reaches below the front edge of the eye. The maxilla exceeds the front edge of the eye. The tongue is slender, slightly concave at the front, and has no teeth. The distance from the dorsal fin to the base of the pectoral fin is greater than the distance from the base of the caudal fin.

2. Age and growth The fry grows rapidly. The fry hatched around April can grow to 2.5 cm in about one month, 4 cm in two months, and 5-6 cm in length after four months. The fry hatched in spring are called "new mouth silverfish", and those hatched in autumn are called "old head silverfish". In winter and spring, they are in the fry growth stage, and they exist at the same time as the parent fish of the spring spawning group. From April to June, the body length is 4-6 cm, and the weight is 0.3-0.9 grams. The life span of this fish is one year, and it gradually dies after spawning.

3. Diet: Taihu Neosilverfish feeds on large zooplankton, cladocerans and copepods throughout its life.

4. Reproduction Taihu New Silverfish has two spawning groups, spring and autumn. The spring reproductive group is generally 5.3 cm to 7 cm long. The spawning period is from early March to mid-May, and the peak period is generally in early to mid-April, with the water temperature around 15°C. The spawning group often lays eggs in the still water of the lake or in the micro-flowing water area of ​​the estuary. The eggs are oval and sinking, and the hatched fry are 3 mm to 3.3 mm long.

The individuals in the spawning group in autumn are smaller than those in spring. The peak production period is mostly in early to mid-October, the water temperature is around 20℃, the eggs are sinking, and the hatched fry are about 2.7 mm.

About the breeding technology of silverfish:

The operation method of artificial breeding of silverfish is basically the same for Taihu new silverfish and big silverfish, but the breeding period is different. The artificial breeding of silverfish is introduced below using big silverfish as an example.

(I) Broodstock

1. The source of broodstock.

Sexually mature individuals caught during the breeding season of whitebait can be used for artificial breeding; individuals raised to sexual maturity can be used for artificial breeding; individuals that have not reached sexual maturity shall not be used for artificial breeding.

2. Catching of broodstock.

Fishing for whitebait should be done during the peak spawning period. Fishing can start in early December in the north of the Yellow River and in mid-December in the south of the Yellow River. The fishing nets can be gill nets (mesh size 2a is 1.5-2.4 cm) or ice drag nets. Parent fish should be caught in spawning grounds where spawning and reproduction are relatively concentrated; when taking fish from the gill net, they should be gently picked from the head.

3. Breeding of broodstock.

Individuals of strong physique, large size and immature gonads caught during the concentrated fishing period of whitebait can be raised as broodstock and must comply with the following regulations:

(1) Broodstock can be raised in cages or ponds.

(2) The specifications of the broodstock cages can be 5m × 5m × 2m, or 4m × 4m × 1.5m, with a mesh size of 0.5cm. The area of ​​the broodstock pond can be 0.2-0.4 hectares, with a water depth of 1.5m.

(3) The stocking density in cages should not exceed 4,000 kg/m3, and the stocking density in ponds should not exceed 0.5 kg/m3.

(4) During the stocking period, sufficient amounts of small fish and shrimp should be released for the broodstock to eat, and stocking management should be strengthened.

4. Selection of broodstock.

Signs of female fish maturity: large and healthy, with a significantly larger abdomen, a small triangular anal fin, eggs can be seen flowing from the abdomen after the fish is lifted, the abdomen is soft to the touch, and eggs flow out when the abdomen is gently pressed, and they are oval, bright, and scattered. Signs of male broodstock maturity: the individual is smaller than the female broodstock, the abdomen is not swollen, the chest of the mature male is rose red, the anal fin is wavy, the scales above the anal fin are large and have suction, and there is a crescent-shaped, milky white testis on the left side of the body cavity above the cloaca.

(ii) Artificial insemination

1. Gender ratio.

The male-female ratio of broodstock used for artificial breeding is 1:2-3.

2. Insemination method.

Dry insemination should be used, and the specific operation method is as follows.

(1) Semen fertilization method. Use the thumb and index finger of your left hand to gently pinch the head of the female fish to lift it up, wipe the water off the fish's body with a dry cloth, and use the thumb of your right hand to gently squeeze the female fish's abdomen from top to bottom to let the eggs flow into the dry fertilization dish. Then take 2-3 male fish in turn, wipe their body surfaces dry, squeeze the semen onto the anal fin, and put them together with the fish into the fertilization dish to be fertilized. Immediately add a small amount of reservoir water filtered through a silk sieve or 0.7% saline, shake and let stand for 1-2 minutes.

(2) Sperm fertilization method. Use pointed tweezers to cut the abdomen of the male fish from the anus to the front, pick out the intestines, pick out the testes and place them in a dry fertilization dish. Use a glass rod or tweezers to crush and grind the testes. Then, place the female fish head up and tail down, and gently squeeze the abdomen from front to back to make the eggs flow into the fertilization dish. Use the male fish's tail fin to stir the sperm and eggs, then add a small amount of filtered reservoir water or 0.7% saline, shake and let it stand for 1-2 minutes.

(III) Hatching of fertilized eggs

The fertilized eggs of whitebait should be incubated at low temperature. The incubation time is relatively long. It takes more than 100 hours from incubation to the mid-gastrula, when the average water temperature is 6℃-7℃, and it takes about 30 days to hatch into fry. If the water temperature is lower, the incubation time will be longer, so the change of water temperature must be controlled during the entire incubation process. The requirements of fertilized egg development for dissolved oxygen should be met to prevent the occurrence and spread of saprolegniasis of fertilized eggs.

The water temperature should be controlled within 1℃-8℃. The water should not freeze or exceed 10℃, otherwise the hatching rate will be greatly reduced or the eggs will develop abnormally. The sudden change of water temperature should be controlled within ±2℃. When changing water, reservoir water with the same temperature in the room can be used. The dissolved oxygen is achieved by changing water. Generally, the number of daily water changes is determined according to the water temperature. If the average water temperature is around 3℃ within the first 3 days, it is better not to move the hatching tray. In the subsequent hatching process, if the daily average water temperature is lower than 4℃, change the water every 2 days. If the daily average water temperature is 5℃-8℃, generally change the water 1-2 times a day. The fertilized eggs cannot be overlapped and squeezed in the hatching tray, otherwise they will die of lack of oxygen or develop abnormally. The water depth of the hatching tray is about 5 cm. There should be no direct sunlight in the hatching room, and it should not be a dark room.

Whitebait breeding technology

1. The habits of large silver fish in the pond.

1. Habitat. They live mostly in the middle and lower layers of the pond. Except for lack of oxygen, they are rarely found in the upper layer. If there are water plants around the pond or on the bottom of the pond, they often drill into them. Larvae and juveniles have a strong tendency to phototaxis. They can be lured into groups by light at night. Therefore, this method can be used to check their growth and feeding conditions. Adult fish do not have this characteristic.

2. Feeding habits. The young fish start eating rotifers at 10 days after hatching. Later, they gradually choose larger and more easily available zooplankton as food, in the order of nauplii, copepod larvae, cladocerans and adult copepods. The whitebait is a carnivorous fish, and its main food is small fish and shrimp.

3. Reproduction habits. In ponds, whitebait can develop to gonadal maturity and lay eggs on their own. The characteristics of gonadal development and spawning are basically the same as those in natural waters. In the middle and lower reaches of the Yangtze River, the peak spawning period is from late December to late January. In hard-bottomed ponds with aquatic plants, spawning is more concentrated and the fertilization rate can reach 80%-90%.

2. Pond conditions.

Choose an old pond with fresh water, no pollution, sheltered from the wind and facing the sun, and convenient water inlet and outlet. The single pond area is 0.2 hectares to 0.3 hectares (1 hectare is 15 mu), the integrated pond area is 0.3 hectares to 0.6 hectares, the pond is more than 2 meters deep, the bottom mud is 0.2 meters thick, and there is a moderate amount of aquatic plants around the pond. Note: Do not mix with animal-eating and omnivorous fish.

3. Stocking and cultivation of seedlings.

1. Prepare the seedling stocking pond. Drag the net from the fish pond, stir the bottom mud appropriately, and then pour the pond water into the stocking pond after dredging and pest control. Because the temperature is low when the whitebait starts to eat, the pond water quality is difficult to cultivate, especially the rotifer density is low. Use the fish pond fertilization water and input the dormant rotifer eggs to quickly increase the bait density in the stocking pond. This work should be completed two weeks before stocking, and the pond water depth should be 0.6 meters before stocking.

2. Source of seedlings. For the first breeding, mature parents can be collected from natural areas, and artificial insemination can be performed on site to obtain fertilized eggs (fertilized eggs are available for sale at the fish farm). Fertilized eggs can be incubated in still water indoors. When the water temperature is maintained at 4℃-6℃, the eggs will hatch in 30-40 days, with a high hatching rate and a better stocking effect. After the hatching of the eggs at the end of February, it is easier to obtain food, which is conducive to improving the survival rate of the seedlings.

3. Stocking method. Stocking in the embryonic stage is more effective than in the fry stage. Put them in the pond for incubation one week before hatching. Put 20,000 fertilized eggs per 667 square meters (1 mu), and 30 kg of large whitebait can be caught from September to October. If the stocking amount is too large, there will be insufficient food for the fry. The pond water depth should be 1 meter to 1.5 meters.

4. Cultivation technology. Larvae feed on rotifers and nauplii. They start to eat 10 days after hatching, and will die if there is no food 3 days after starting to eat. Therefore, the stocking pond should be fertilized in advance to ensure that there is enough food when they start to eat. The cultivation bait is fully fermented manure, and lime water is applied appropriately. After 10-15 days, the water becomes concentrated and the rotifers can reach a considerable density.

Fertilizers can be applied frequently during the juvenile stage of whitebait. The amount of fertilizer can be controlled according to the water color and temperature. Try to make the pond water transparency reach more than 40 cm and the water depth maintained at 2 meters.

4. Adult fish farming.

1. Provide sufficient bait. Adult fish (total length over 40 mm) have a large food intake and significantly faster growth rate. Fertilizers must be applied frequently to maintain the density of plankton. Fertilizers should be decomposed and fermented, or a small amount of soybean milk can be sprinkled. Use 250-500 grams of soybeans per 667 square meters of water surface every day, and flexibly control according to water quality conditions.

2. Strictly prevent floating. Whitebait has a higher requirement for dissolved oxygen than ordinary fish, and will always float first when mixed with other fish. When the water temperature is 20℃, floating occurs. If emergency measures are not taken immediately, a large number of deaths may occur. The way to prevent floating is to reduce the amount of fertilizer and prevent the over-reproduction of bait organisms. If the water is too fertilized, fresh water should be replaced as soon as possible. If necessary, an aerator or oxygenator can be used to increase oxygen.

3. Pay attention to the change of feeding habits. There is a transition period for the feeding habits of whitebait, which gradually changes from eating cladocerans and copepods to carnivorous. When fish and shrimp are found in the intestines of whitebait with a body length of nearly 80 mm, it means that the feeding habits are changing. Small fish and shrimp should be introduced in time and maintained at a certain density to promote the growth of whitebait. In May, the Yangtze River Basin can introduce appropriate egg-carrying shrimps, and the hatched shrimps are just right for the whitebait to eat during the transition period.

4. Prevent high temperature. In hot seasons, the pool water should be kept at a depth of more than 2.5 meters, and shading measures should be taken when necessary to prevent high temperature hazards.