When it comes to invasive fish, it is estimated that many people have the impression that in the south, especially in Guangdong, Fujian, Hainan and other regions, there are many invasive fish in natural waters, resulting in a sharp decrease in the density of native fish.
As we all know, Qiandao Lake is known as "the world's first beautiful water", when the water quality is good, the transparency can reach more than 10 meters.
In the 90s of the last century, the water quality of cyanobacteria broke out in the Qiandao Lake reservoir area deteriorated, and the water quality was improved by releasing filter-feeding fish such as silver carp and bighead carp in the reservoir area, allowing them to swallow plankton and zooplankton, so as to achieve the purpose of controlling the water with fish.
The effect of this fish water control is very good, just more than ten years to make the water quality of Qiandao Lake reach the top of the country, not only the water quality is good, and the fish of Qiandao Lake is also called "organic fish", becoming the country's first organic fish breeding base, and through the national certification.
In other words, in the 90s of the last century, Qiandao Lake caused an outbreak of cyanobacteria due to pollution, which gave Qiandao Lake a new lease of life by treating water with fish, so what kind of fish is the invasive fish in Qiandao Lake this time? Is it possible to "cure fish with fish"?
1. Fish of Qiandao Lake
In 1955, the construction of the Xin'an River Reservoir began. In 1959, the Xin'anjiang Hydropower Station was sealed and stored water. In 1960, the Xin'an River Reservoir was completed. On December 15, 1984, the Zhejiang Provincial Geographical Names Committee officially named the Xin'anjiang Reservoir as "Qiandao Lake".
Located in Chun'an County, Hangzhou City, Zhejiang Province, a small part of which is connected to the northwest of Jiande City, Hangzhou City, it is an artificial lake formed by the construction of Xin'anjiang Hydropower Station to impound the upper reaches of Xin'an River. After the completion of the Xin'an River Reservoir, the dam intercepted the upper reaches of the Xin'an River into a huge lake.
The reservoir dam is 105 meters high and 462 meters long; The reservoir is about 150 kilometers long, the widest point is more than 10 kilometers, the deepest point is more than 100 meters, the average water depth is 30.44 meters, under the normal water level, the area is about 580 square kilometers, and the water storage capacity can reach 17.8 billion cubic meters.
The basin area above the dam site of Qiandao Lake Reservoir is 10,442 square kilometers, of which 60% of the basin area (catchment area) is in Anhui Province, the main source water is the Xin'an River and its tributaries in Anhui, and the catchment water comes from Shexian, Xiuning, Tunxi, Jixi in Huizhou, Anhui Province, as well as the southern part of Qimen and Huangshan District, and there are 33 rivers entering the reservoir.
There are 33 rivers in the reservoir and a water surface of 580 square kilometers, and it is not an exaggeration to say that Qiandao Lake is a super large artificial lake. According to statistics, 114 species of fish have been identified in the waters of Qiandao Lake.
This is a lot of more than 100 species of fish, and it is estimated that people living near Qiandao Lake may not be able to identify all of them, of which 9 alien species account for 5.61%. (Source: Chun'an County Agriculture and Rural Bureau)
These species include bluegill sunfish, Nile tilapia, gillied tilapia, spotted catfish, largemouth bass and pike, all of which are found in the Qiandao Lake area, with two invasive fishes, bluegill and Nile tilapia, also occurring in the river environment.
It can be seen that some of these fish have adapted to the ecological environment of Qiandao Lake, and have even spread to the rivers around Qiandao Lake.
2. What are these 9 invasive fish?
Each of these invasive fish has its own characteristics, some are super reproductive, some are breeding to protect the eggs from other fish until the juveniles are able to live independently, and some are super aggressive.
Blue-gills sunfish is native to North America and is found in the freshwater waters of Ontario, Canada, southern Quebec to the Great Lakes of United States, many southern states and northern Mexico. In 1987, the Chinese Fisheries Society introduced it to Beijing and Hunan Province for trial breeding.
In the same year, Hubei Provincial Fisheries Research Institute introduced the fish fry from United States; In 1998, Dongguan and Shunde cities in Guangdong Province also introduced the fish from United States. It can safely overwinter under the natural conditions of Beijing, Hunan, Hubei and other provinces and cities. It likes to swim in groups and is very adaptable.
Nile tilapia, native to the Nile River system in Africa, has strong adaptability, omnivorous, rapid growth, strong fecundity, strong territorial awareness and juvenile protection behavior. Through competition, predation and other effects, there is a great threat to native fish.
In July 1978, the Yangtze River Fisheries Research Institute successfully brought 22 samples of Nile tilapia of 2-3 cm from the Blue Nile River in Sudan to Shashi. In October 1979, it was promoted to the whole country.
Gili tilapia and gilly tilapia are new salt-tolerant varieties suitable for commercial seawater aquaculture produced by hybridization of Nile tilapia new Jifu variety and Salo tilapia as the male parent, which are hybrid varieties.
The most suitable temperature for growth is 28-32 °C, resistant to low oxygen, and can live in sea and fresh water. Sexual maturity is early, fecundity is strong, and it belongs to the reproductive type of oral breeding of female fish.
Spotted catfish, native to the Americas, mainly distributed in most countries in North America, Southeast Asia and some countries and regions in Western Europe are also distributed, spotted catfish is a high-quality species of freshwater aquaculture, belonging to large fish giant individuals of more than 20 kg.
First introduced to the mainland in 1984, catfish are heterogeneous, resistant to disease, adaptable, fast-growing, and large. It is cultivated in more than 20 provinces, municipalities and autonomous regions in mainland China.
Largemouth bass, native to freshwater rivers and lakes in North America, can survive in the range of water temperature 1~36 °C, and begin to feed above 10 °C. Juveniles feed on zooplankton, and after reaching 3.5 cm in length, they mainly feed on fish and shrimp, and are carnivorous fish, and often cannibalistic when food is scarce.
Largemouth bass was introduced to the mainland in the early 80s of the 20th century, and has been cultivated and promoted in the mainland since 1983After more than 40 years of development, largemouth bass has become one of the important freshwater aquaculture species in mainland China, and is cultivated in Guangdong, Jiangsu, Hubei, Shanghai, Shandong and other places.
Pike and pike are distributed in the alpine rivers of Asia, Europe and North America, and are only distributed in the lower reaches of the main stream of the Irtysh River and its tributaries Haba River, Burjin River, Klan River and Kara Irtysh River. It prefers lakes with tributaries and slow-flowing rivers, usually inhabits aquatic plants, and lives in cold regions.
Pike has a fast growth rate and delicious flesh, which plays a role in inhibiting the reproduction of small fish populations in the lake, and is one of the economic fish in Xinjiang Autonomous Region. It is a giant fish, and adult females can even exceed 1.5 meters in length and weigh up to 50 kilograms.
These six species of fish already have a certain population in Qiandao Lake, and bluegill sunfish and Nile tilapia have spread to the surrounding rivers, among which bluegill sunfish ranks sixth among the 114 fish species in Qiandao Lake, which shows how dense the population of bluegill sunfish is.
The other three species of invasive fish, the specific species, the official did not say, it should be that the population density is not large, and the impact on the ecological environment in Qiandao Lake is not clear.
3. The harm of invasive fish to Qiandao Lake
Since exotic fish have no natural predators in the waters of Qiandao Lake, alien fish species will multiply in large numbers, which may damage the original aquatic ecosystem and endanger the diversity of aquatic animals and plants.
Take the sunfish with the largest population, the breeding period of the sunfish lasts from April to November, which means that there are 7 months of the year to reproduce, and the super reproductive ability seriously crowds out the growth space of native fish, and it is not just as simple as fast reproduction.
Sunfish are adaptable, ferocious by nature, love to eat fish eggs, and devour large quantities of fish eggs, causing other fish populations to grow slowly. Regardless of the small size of the sunfish, its back spines are relatively long, which can effectively block the devouring of large fish, so that it can reduce the chance of being preyed on by large predatory fish, thus ensuring its survival.
The population of the bigeye bream in the Qiandao Lake reservoir area is slowly decreasing, which is likely to be related to the sunfish, because there are many sunfish in the breeding grounds of the bigeye bream, and it is possible that the eggs of the bigeye bream are swallowed by the sunfish in large quantities.
Speaking of tilapia, the reproduction of tilapia is very peculiar, after spawning, the female tilapia will hold the fertilized eggs in the mouth to hatch, and the hatched juveniles can also hide from the enemy in the mouth of the female, even after the eggs hatch, the tilapia will not leave immediately, but wait for the seedlings to have the ability to forage freely, and the adult fish will leave.
As a result, the survival rate of tilapia seedlings is very high, resulting in the rapid growth of tilapia populations in Qiandao Lake. It's not just tilapia that has a high hatchability of eggs and a high survival rate, but largemouth bass reproduces in a similar way to it.
During the breeding season, the males of largemouth bass dig holes with their tails, build nests, and lure females into the nest to lay eggs. When the female gives birth, she is chased away by the male, who is responsible for guarding the hatching of the fertilized eggs. After the eggs hatch, the male does not leave immediately, but guards the seedlings and only leaves when the seedlings have the ability to feed.
And the largemouth bass is a carnivorous fish, mainly feeding on fish and shrimp, the largest record of largemouth bass caught in natural waters is more than 10 kilograms, fortunately the individual is not large, if the individual is huge, it is a disaster for other fish growing in the waters! However, the pike belongs to the "vicious dog" through and through!
Pike is a giant predatory fish, in the past, pike has been supplied by fishing natural fish, its natural resources have been very limited, and even extinct in some rivers, it is a rare and precious cold-water fish, and is included in the mainland's "List of National Key Protected Economic Aquatic Animal and Plant Resources (First Batch)".
However, don't underestimate this fish, this is just caused by overfishing, in fact, the pike is very ferocious, ferocious, in the place of origin to the surface of the water birds, all the fish smaller than it at the bottom of the water, and the same kind of food, in addition to breeding seasonally mature broodstock stop feeding, feeding throughout the year.
As long as the fish is smaller than it, it will rely on its own full mouth of fangs to rush up and bite a few bites, and when it comes to the breeding period, the female dogfish after breeding will not let go of even the male dogfish, because the male dogfish is smaller than it, this way of eating pike, do you say ferocious or not?
Sunfish reproduce 7 months a year and devour a large number of eggs; Tilapia has a high hatching rate of eggs in the mouth, and its feeding habits are similar to those of many fish when they become adults, which seriously crowds out the living space of native fish. The largemouth bass guards its young and does not leave until they are able to move freely, and the larvae have a high survival rate and are carnivorous fish, devouring large amounts of other fish.
The pike belongs to a proper vicious dog, although it is a rare and precious cold-water fish, the meat quality is better, but Qiandao Lake is not its origin, this fish has no natural enemies, and its growth causes a lot of fish death. It has to be said that the survival of these fish species in Qiandao Lake has a serious impact on the ecological environment in Qiandao Lake.
4. Use fish to treat fish and release big-eyed mandarin fish
Qiandao Lake's foraging of "treating water with fish" has been a great success, so can the model of "treating fish with fish" be applied? Don't mention it, Qiandao Lake has already done this, by releasing the predatory fish in the lake, increasing the density of predatory fish, so as to control the alien fish.
In 2023, the headline of the report of "Chun'an Procuratorate" is: "300,000 bigeye mandarin fish swim into Qiandao Lake, and it is so important to breed and release them!" "The reason why so many mandarin fish are released is to control the problem of sunfish.
Wild mandarin fish has always been loved by people because of its delicious meat and rich nutrition, and the huge market demand has led to a number of cases of illegal fishing and acquisition of mandarin fish, resulting in a sharp decline in wild mandarin fish resources.
In recent years, alien species represented by sunfish have begun to multiply in large numbers, posing a great threat to the indigenous fish population of Qiandao Lake and seriously affecting the diversity of aquatic life and the stability of the ecosystem. As the natural enemy of the sunfish, the mandarin fish can effectively curb the growth of the sunfish. So can mandarin fish really curb the sunfish population? We can draw conclusions from comparisons.
Sunfish feed mainly on zooplankton and aquatic insects, but also on aquatic plants, small trash fish and small molluscs. Mandarin fish (released this time, bigeye mandarin fish) is a carnivorous and ferocious fish. In spring, swim to shallow shores to feed, feeding on fish and shrimp. Winter activities are reduced, and they spend the winter in rocky caves.
The bigeye mandarin fish is an apex predator in freshwater ecosystems with a highly developed digestive system. In its natural environment, bigeye mandarin fish feeds all year round, and its food composition changes with the seasons. In spring and winter, the diet is mainly composed of fish, shrimp and plant detritus, and in summer and autumn, the food composition of the bigeye mandarin fish is more complex and diverse, including not only fish and shrimp, but also Coleoptera larvae, insect eggs and freshwater shellfish.
Sunfish are relatively small, the common ones are 50-100 g/tail, and the large ones are about 2 kg/tail. Mandarin fish in Qiandao Lake once caught giant individuals weighing dozens of catties. I think it's a matter of size to determine whether a mandarin fish can prey on sunfish.
If you compare the body size of the sunfish with the bigeye mandarin fish, the adult bigeye mandarin fish can indeed prey on the sunfish, so as to achieve the problem of curbing the sunfish population, but the bigeye mandarin fish cannot be expected to eliminate the sunfish, after all, the growth rate of the bigeye mandarin fish is too slow, even if it can devour the sunfish, it is difficult to achieve balance, because the sunfish reproduce too fast.
Native species such as blackfish and squid can be released into the lake through the mode of breeding and release, which are larger in size and can devour large numbers of sunfish when they become adults, thereby curbing the sunfish population.
So what about the other alien fish in Qiandao Lake? It should be said that it is very difficult to do, and there is basically no way. Because adult tilapia are huge, even reaching more than 10 catties, such a large body size is rarely swallowed even by carnivorous fish.
The pike is more ferocious, this fish is estimated to not be able to shake its status even if it is an adult pike, because the body shape of the pike and the pike is not much different, and the pike has sharp teeth, it is estimated that the pike is not bad if it does not find trouble with the pike.
Let's talk about the spotted catfish, this fish has a certain economic value, many provinces have farmed, this large fish is often more than 10 catties after adulthood, and even dozens of catties of giant individuals, such a large individual even if it is a predatory fish, it is difficult to compete with it! It is also more difficult to curb their populations.
Finally: 9 species of fish invaded Qiandao Lake into a mess, is it feasible to release mandarin fish and devour alien species? I think this method is feasible, after all, the size of mandarin fish is larger than that of sunfish when they are adults, and mandarin fish can curb the population of sunfish to a certain extent.
But if you expect mandarin fish to curb tilapia, pike, largemouth bass, and spotted catfish, you have more than enough strength, because these fish are much larger than its individual, especially pike, and pike will definitely devour mandarin fish in reverse, so it is difficult to expect mandarin fish to eliminate the alien fish in Qiandao Lake, what do you say?
References: Encyclopedia bluegill sunfish, Nile tilapia, gilly tilapia, spotted catfish, largemouth black and white pike
"Chun'an Procuratorate" Mountain Prosecutor|300,000 big-eyed mandarin fish swam into Qiandao Lake, and it turned out to be so important to breed and release!
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