Key Points of Early Spring Artificial Breeding Technology for Pufferfish
In recent years, the artificial breeding technology of the obscure puffer (Takifugu obscurus) has become increasingly widespread, and its fry production level has also developed rapidly, gradually forming a new type of high-efficiency aquaculture industry. In order to further improve the production technology level, the Baimao Shunlong Fish and Shrimp Nursery in Changshu City, Jiangsu Province conducted an early spring artificial breeding trial of the obscure puffer in February 2003 and achieved satisfactory results. This technology is now provided to industry professionals for reference, with the hope of practicing and exploring it together.
I. Trial Process and Results
From February 15 to March 5, 3 batches of obscure puffer broodstock were induced to spawn, totaling 30 groups, yielding about 1.8 million eggs, with an average fertilization rate of 70%, and the number of fertilized eggs was about 1.26 million. About 960,000 obscure puffer fry were obtained through hatching, with an average hatching rate of 75%. By April 15, about 500,000 obscure puffer summer fingerlings had been reared, among which about 100,000 were of a size with a body length of 3.0cm or more, and about 400,000 were of a size with a body length of about 2.5cm.
On April 13, some obscure puffer summer fingerlings were stocked in earthen ponds inside a plastic film greenhouse for continued rearing. The earthen ponds had an area of 180 sq m (30m×6m), a water depth of 0.8m to 1.0m, and there were 4 ponds in total, with each earthen pond stocked with 15,000 obscure puffer summer fingerlings of a size of 2.5cm body length. During the stocking process, compound feed for obscure puffer juveniles was fed, the principle of “four fixeds” was adhered to, and attention was paid to water quality management. On April 21, 24 fry were sampled and tested, with an average individual body weight of 3.4g and an average total length of 4.3cm. On May 21, 12 fry were sampled and tested, with an average individual body weight of 25g. On May 23, a total of 57,000 obscure puffer juveniles were caught and moved out of the greenhouse to be stocked in open-air fish ponds for continued rearing. There were 2 open-air fish ponds, totaling 16 mu, with an average stocking density of 3,600 fry/mu, and compound feed for obscure puffer juveniles was fed. By mid-July, some obscure puffer of a size of about 100g each were caught and sold.
II. Artificial Breeding Technology
1. Broodstock Overwintering
On October 20, 2002, obscure puffer broodstock were selected and moved from outdoor fish ponds into greenhouse fish ponds for overwintering. The greenhouse fish ponds had an area of 100 sq m (10m×10m) and a water depth of 0.8m to 1.0m. The broodstock stocking density was 1 fish/cubic meter to 2 fish/cubic meter, and female and male individuals were stocked separately in different ponds. During the overwintering period, the water temperature was kept relatively stable, with the lowest not below 16°C and the highest not above 18°C. The feed was mainly mussel meat, supplemented by artificial compound feed, with a daily feeding amount of 2% to 3% of the broodstock body weight. In water quality management, sewage was siphoned and drained and water was added once a week, with each water addition being about 1/4 of the total water volume. Around January 20, 2003, pre-spawning cultivation began, with the water temperature at the lowest not below 18°C and the highest not above 22°C, and micro-flow stimulation was carried out for 6 hours to 12 hours every day, with a water flow rate of about 15 cubic meters/hour. The water source was mainly the circulating pond water from the fish ponds, and the feeding amount was appropriately increased at the same time.
2. Spawning Induction
On February 15, 2003, obscure puffer broodstock with well-developed gonads were selected for spawning induction. The spawning agent was injected in 2 doses. In the first injection, female broodstock were injected with 2μg LRH-A2, while male broodstock were not injected. The second injection was given 24 hours to 36 hours after the first injection, with female broodstock injected with 10μg + PG2mg + DOM1mg LRH-A2, and the dose for male fish was halved. Artificial insemination was carried out within 12 hours to 36 hours after the second injection, using the dry method of artificial insemination. The fertilized eggs were de-adhered with 0.6% saline for 10 minutes to 15 minutes, and after rinsing off the saline, the number of fertilized eggs was estimated and then placed into the incubator. During the spawning induction period, the water temperature was controlled at 20°C to 22°C, and the temperature difference between day and night did not exceed 2°C.
3. Hatching
The hatching tool was a shallow-water static incubator, which was a square foam plastic container with a volume of 50cm×50cm×10cm. Each incubator was filled with 4cm to 6cm of shallow water, and when the water volume was 6L to 8L, 20,000 to 30,000 obscure puffer fertilized eggs could be placed in it. During the hatching period, the water temperature had to be kept stable at 21°C to 23°C, and the water was changed and the fertilized eggs were rinsed 2 times a day. The hatching water had to undergo pre-storage, aeration, drug disinfection, temperature difference adjustment, and other treatments before use. The fertilized eggs of the obscure puffer hatched out of the membrane after 96 hours to 120 hours, and the newly hatched larvae should be promptly moved to the fry rearing pond.
III. Early Rearing of Obscure Puffer Fry
Obscure puffer fry from early spring breeding must be reared in ponds inside a greenhouse, with the water temperature maintained at 22°C to 25°C, a rearing pond area of about 20 sq m, and a pond depth of 0.8m to 1.0m. At the beginning of stocking, a water depth of 30cm to 40cm was sufficient, and each pond could be stocked with 250,000 to 300,000 fry. After 4 days to 5 days of rearing, the juveniles began to feed, and rotifers should be fed in a timely manner, 4 times to 6 times a day. The feeding amount of rotifers should be controlled so that their density in the water body was preferably 8 individuals/ml to 10 individuals/ml. After feeding rotifers for 4 days to 5 days, when the juveniles grew to a body length of 0.5cm, they could be switched to feeding Artemia, and the feeding amount should be controlled so that their density in the water body was preferably 2 individuals/ml to 3 individuals/ml. During this period, sewage was siphoned, water was drained, and new water was added once a day, gradually increasing the water level to 80cm to 90cm. After feeding Artemia for 4 days to 5 days, when the juveniles grew to a body length of about 1.0cm, they could be moved into large ponds for the middle rearing stage, feeding on zooplankton such as cladocerans and copepods. After the juveniles reached a body length of 2.0cm, they could be trained to eat artificial compound feed.