How to Transplant Large Icefish? Detailed Technical Explanation for Hinggan League, Inner Mongolia

Hangali Reservoir is located in Horqin Right Wing Middle Banner in the northeastern part of Inner Mongolia Autonomous Region, and is a medium-sized lateral reservoir on the Huolin River. In January 1996, 780,000 fertilized eggs of large icefish were transplanted from Luhun Reservoir in Henan Province and placed under the ice for natural hatching, and the hatching results were very good. A growth inspection that year found that the transplanted large icefish grew and developed well, reached sexual maturity in late December, and began natural reproduction, achieving a first-class introduction effect. In January 1997, in order to consolidate the number of the supplementary population of large icefish, another 1 million fertilized eggs of large icefish were released into the reservoir, and by the trial fishing in September of that year, the large icefish had grown to 12-14 cm. Because the reservoir had no fishing capacity or equipment at that time, a boat was hired from Taihu Lake in Jiangsu to fish. Due to the long distance, the timing was missed. That year only 370 kg of commercial large icefish was caught. In the third year after transplantation, the output of large icefish in Hangali Reservoir reached 24 tons, forming a fishery effect. Afterwards, the output continued to climb, and by 2001 and 2002 the output stabilized at more than 60 tons. In 2003, the reservoir's danger-removal and reinforcement project was completed, the water storage capacity increased, and that year the output of large icefish reached 85 tons; in 2004, the large icefish grew well, and fishing has now begun, with the output expected to remain at around 80 tons. Hangali has now become a model for the successful transplantation of large icefish in northern reservoirs.

Due to the successful transplantation of large icefish, Hangali Reservoir obtained enormous economic benefits. In view of the situation in many other waters in Inner Mongolia where, after successful transplantation of large icefish, the output could not be stabilized, and the large icefish even disappeared on their own, we carried out research on high and stable yield techniques for large icefish in Hangali Reservoir. The specific situation is reported as follows:

I. Adopt artificial measures to increase water productivity

1. Do a good job in ecological construction within the reservoir's watershed area, and maximize the potential of reservoir resources. The Inner Mongolia region suffers drought nine years out of ten, and land desertification is severe. Every year, large amounts of yellow sand are blown by the wind into the reservoir and channels, severely eroding the reservoir and channels. For this reason, the Hangali Reservoir Management Office opened up a 100-hectare ecological protection zone upstream of the reservoir, planting grass and trees in the protection zone to prevent wind and fix sand, conserve the soil, effectively protect the environment around the reservoir, and enhance the potential of reservoir resources.

2. Protect the water body from pollution, and ensure Hangali Reservoir's status as a pollution-free aquatic product production base. Hangali Reservoir is a lateral reservoir of the Huolin River. There is no industrial zone upstream, farmland within the watershed is scarce, the water quality is good, and it has superior conditions for producing pollution-free aquatic products. Large icefish is a major export-earning species among our region's aquatic products. After joining the WTO, China's economy has gradually become integrated with the world economy, and the quarantine and inspection systems for aquatic products have also become increasingly complete. Therefore, to maintain the long-term vitality of large icefish, work to prevent pollution of the water area must be done well now. Hangali Reservoir is one of the first certified pollution-free aquatic product bases in our region. At present, bighead carp, common carp, and crucian carp have passed national certification and become pollution-free aquatic products, and other species are also actively applying. The aquatic products of Hangali Reservoir have registered the "Yinjian" brand trademark with the State Administration for Industry and Commerce.

3. Adopt corresponding measures such as fertilization and water quality regulation to increase the primary productivity of the water body. In May and June, Hangali Reservoir uses surplus fertilizer from agricultural and pastoral areas and puts fermented organic fertilizer into key reservoir bays where large icefish are concentrated. First, it supplements the nutrient salts in the water body and provides a material basis for the reproduction of plankton in the reservoir; at the same time, the large amount of organic debris precisely makes up for the shortage of zooplankton in the water body in spring, and provides an abundant bait base for juvenile large icefish. Exogenous nutrients brought in with water are also an important source of nutrient salts in the reservoir. Increasing the water exchange volume of the reservoir can improve the primary productivity of the reservoir, and thereby increase the output of large icefish in the reservoir.

II. Adopt human measures to create good survival conditions for large icefish

1. Reduce the species that prey on large icefish. Because large icefish are relatively small and have relatively weak swimming ability, they are targets of predatory fish in the middle and upper layers. Therefore, the influence of predatory populations must be reduced. Predatory fish in the water area must be controlled below 5% for the population development of large icefish to benefit. Hangali Reservoir has been in operation for more than 20 years, and there are many middle- and upper-layer predatory fish in the reservoir, such as Chinese hooksnout carp, sharpbelly, Amur ide, and redfin culter. In order to create a good living environment for large icefish, in 1997, when the time for catching large icefish was already late, we decisively switched to catching other wild and miscellaneous fish. That year, more than 3 tons of various wild and miscellaneous fish were caught; in 1998, more than 5 tons were caught, fundamentally changing the fish structure of the reservoir, and large icefish quickly became the dominant fish population in Hangali Reservoir.

2. Reduce low-value fish that compete with large icefish for bait. Since the reform and opening up, people's living standards have improved greatly. People are no longer satisfied with the supply of low-grade aquatic products, and the traditional "four major Chinese carps" have been challenged. Large icefish, due to characteristics such as high protein content and delicious taste, was quickly accepted by people. Coupled with the influence of the international market, the price soared all the way, making it a darling of the market. The stocking amount of silver carp and bighead carp in Hangali Reservoir has always been insufficient, and there are no other fish that mainly feed on plankton, so the bait for large icefish is relatively abundant. However, in the future, the stocking amount of silver carp and bighead carp should be further controlled to provide an even more abundant bait environment for large icefish.

III. Adopt scientific measures to ensure the resources of large icefish

1. Set up year-round protection zones. The population structure of large icefish is simple, and 100% of the recruited number is the supplementary population of the current year. Therefore, the size of the supplementary population directly affects the fishery output of the current year. Therefore, we must designate 5%-10% of the water area in the reservoir as year-round protection zones. Within the protection zones, no fishing gear is allowed to enter for fishing at any time, making them safe places for large icefish to reproduce and live. This protects part of the large icefish, continuously provides supplementary populations for the large icefish population, and increases resources.

2. Determine a reasonable retained stock of large icefish resources. After the successful transplantation of large icefish in Hangali Reservoir, we conducted investigations and studies on the distribution, feeding habits, and reproductive habits of large icefish in the water area. We carried out resource assessment to determine reasonable catch and retained stock. Stipulating the catch is mainly to ensure that sufficient retained stock is left. This preserves enough spawning parent fish while also obtaining a relatively high fish yield. However, how to reasonably determine the retained stock of large icefish resources is very difficult work. Our current practice is to stop fishing when the daily catch of a pair of trawlers is about 100 kg, and take the remaining large icefish as the retained stock.

3. Set up fish-blocking grates in front of the sluice gate to reduce the loss of large icefish resources with the water. After several years of observation of large icefish, we did not find the phenomenon of large icefish swimming upstream against the current, but there is a phenomenon of escape downstream with the current; especially in years with a relatively large water exchange volume, the escape phenomenon is more serious. After 2000, in order to prevent large icefish from flowing downstream, we set up fine-mesh fish-blocking grates in front of the reservoir outlet, which played a good role in preventing escape.

IV. Scientific management and prevention of fish diseases

Reservoir fish diseases have always emphasized "prevention" over "treatment." Large icefish are open-water fish and have a relatively short life cycle, so fish diseases are also relatively few. However, the large icefish Bothriocephalus disease that occurred in neighboring provinces and cities sounded a warning for waters where large icefish transplantation had succeeded. Bothriocephalus is widely present in reservoirs in Northeast China. Because it previously mainly parasitized small miscellaneous fish, it had long received little attention. Large icefish infected with Bothriocephalus experience atrophy of the reproductive organs and cannot reproduce naturally normally. Moreover, transplanted waters need to collect fish eggs from outside every year for propagation to supplement the number of the remaining population. This consumes a great deal of manpower, material resources, and financial resources.

There is still no very effective method for treating fish diseases in reservoirs. Starting from cutting off the life cycle of Bothriocephalus, we adopted some active preventive measures. The main one is to control the final hosts of Bothriocephalus - birds. This reduces the chance of large icefish being infected.

V. Artificial propagation and release to increase the number of the supplementary population

After large icefish spawn in natural waters, due to the influence of various factors in the water body, their fertilization rate and hatching rate are both very low. In order to ensure the number of the supplementary population in the water area, in addition to ensuring a reasonable retained stock, timely catching sexually mature parent fish for artificial propagation and returning the fertilized eggs to the original water area to supplement and prevent insufficient natural egg production and increase the number of the supplementary population is a means of artificially enhancing large icefish resources. Starting from the winter of 1997 after the successful transplantation of large icefish, we have carried out artificial propagation activities for large icefish in Hangali Reservoir every year. Practice shows that this measure is very effective.

VI. Strengthen fishery administration and do a good job in resource protection

Resource protection is an important measure for transplanting large icefish, enhancing fishery resources, and ensuring the sustainable use of fishery resources. Practical implementation measures for the protection of large icefish transplantation and enhancement must be formulated. The large icefish reproduction protection zone, closed fishing zone, and closed fishing period must be determined, the "Fishery Law of the People's Republic of China" must be strictly implemented, and all harmful behavior that damages large icefish resources must be eliminated.

Large icefish is an excellent aquatic variety, and the artificial transplantation technology should be mastered by the state or scientific research departments to ensure its purity and carry out scientific and rational promotion. It is not suitable for individuals to promote this excellent variety. The state should also incorporate it into seed law management to more effectively ensure the promotion of large icefish domestically and even internationally.