The two most delicious fish in Qiandao Lake are now difficult to catch, just because of this "invader"?

Recently, a reader of Zhejiang Express named "Zhu Er" posted on Chengshi Interactive:

There are as many blue stripes as before, but no red pigs or yellow tails. An old fisherman said that in recent years, the alien species sunfish has reproduced in large numbers and eaten other fish eggs, which has become a disaster. You can indeed see young sunfish on the shore, but they are not delicious and the meat is very rough.

Another reader, "Zuoyou Wo Meng", also saw sunfish in Qiandao Lake:

There should be a lot of sunfish in Qiandao Lake. One of our summer camp activities is to experience fishing like fishermen. We put down the silk net in the evening and pull it up in the morning. One net can usually catch more than 10 fish, most of which are green silk as long as a pen, and the rest are two or three sunfish. Sunfish are very small, the largest one is only the size of a newborn baby's palm.

The reporter consulted Gu Dang'en, an expert on alien species at the Pearl River Fisheries Research Institute. He said that the pictures posted by "Zhu Er" were mostly of sunfish. There was a picture taken on the shore, but due to the resolution, it was impossible to tell what kind of fish it was. However, according to preliminary judgment, there were indeed sunfish in the pictures of "Left and Right My Dream", and there were more than one species, including bluegill sunfish, green sunfish, and long-eared sunfish.

What is this sunfish that everyone is talking about? What impact has the larger alien species behind it had on my country's native waters?

Sunfish, a fertile species, once thrived wildly in Japan

Let’s first get to know the sunfish——

Sunfish is not a single species, native to freshwater waters in the southern United States and northern Mexico. Adult fish are 24-40 cm long, and individuals are smaller. The most striking feature of the appearance of sunfish is that there is a black, ear-like soft membrane on the rear edge of the gill cover, which is a common feature of all sunfish, but the "eardrum" of different species has different colors and shapes.

Sunfish have a strong reproductive capacity, spawning many times between May and August, with large numbers of eggs that usually hatch in about five days. Newborn sunfish require no care and can thrive by eating some plankton on their own.

This fish is also particularly resistant to freezing and can survive in water temperatures between 1 and 38 degrees Celsius. In the waters of northern my country, when the water temperature is 2 degrees Celsius in winter, it can still safely spend the winter in natural waters.

The ability to reproduce, survive with a little food, and not afraid of the cold mean that if left uncontrolled, sunfish will become an alien invasive species and cause harm to the aquatic ecology.

There are such examples in Japan.

In 1960, when Crown Prince Akihito of Japan visited the United States, he received a gift from the mayor of Chicago, which was a batch of sunfish.

Akihito fell in love with sunfish because of its high appearance and good taste. After returning to Japan, he immediately promoted the breeding of sunfish in the country with his preference for sunfish.

Between 1963 and 1964, in order to further expand the reproduction of sunfish, they were released into Lake Biwa, the largest lake in Japan.

The sunfish that entered Lake Biwa began to reproduce wildly, and soon they were no longer limited to Lake Biwa, but began to spread to various waters in Japan. Due to their rapid reproduction, few natural enemies, and abundant food, the sunfish became a disaster.

These fish not only squeezed the living space of native fish in Japan, but also preyed on the eggs and fry of native fish in large quantities, causing the number of native fish to drop sharply. By around 2010, sunfish had spread all over Japan's lakes, rivers, and even sewers, eventually causing at least five species of native fish to disappear, and forcing the minnow to become a rare species, forcing the fishery department to tailor-make protection measures for the minnow.

Sunfish is indeed the most harmful alien species in Qiandao Lake.

The reporter contacted Shen Peng, a staff member of the Chun'an County Fishery Administration and Port Supervision Bureau, who said: "The sunfish is currently the most harmful alien species in Qiandao Lake."

At the beginning of this century, some sunfish escaped into Qiandao Lake during the cage management. However, it did not attract much attention at that time because people thought that this kind of tropical fish could not adapt to the low temperature of Qiandao Lake in winter and would gradually die out.

Unexpectedly, the sunfish have adapted to the water temperature of Qiandao Lake. "The water of Qiandao Lake is very deep, and there is a normal temperature layer in the deep water layer, which keeps the water temperature at more than 20 degrees Celsius all year round. The sunfish survive here and reproduce in large numbers," said Shen Peng.

In 2016, things started to develop in an unexpected direction. The fish species, quantity and scale reported by the model fishermen frequently showed sunfish, and the fishermen said that most of the fish caught were small sunfish. Shen Peng explained that sunfish are an alien species and have no natural enemies in Qiandao Lake. Once they multiply, they will be out of control.

Subsequently, Chun'an Fisheries Administration and Shanghai Ocean University conducted a research project on alien species control and began to scientifically control sunfish, with two specific measures:

First, people were required to catch the fish by hand, distributing small nets to fishermen to catch sunfish. However, this method was very laborious because sunfish can lay eggs 4-5 times a year.

Second, biological control, big fish eat small fish. Use the mandarin fish, which also lives in the mesothermic layer and is larger in size, to eat the sunfish.

"We have been increasing the amount of mandarin fish released each year, but to know exactly how many sunfish there are in Qiandao Lake and how long it will take to basically control them, we have to wait for Shanghai Ocean University to make a scientific calculation."

Shao Qingjun, a professor at the College of Animal Science of Zhejiang University, also told reporters: Sunfish is an alien species that can survive in low water temperatures. It will have a destructive effect on the fertilized eggs and young fish of the native fish of Qiandao Lake. It cannot be released in Qiandao Lake, otherwise it will have an adverse effect on the native fish of Qiandao Lake. It is strictly forbidden to release it in open waters such as rivers, lakes, etc. to avoid ecological pollution caused by alien species.

For fishing enthusiasts, the appearance of sunfish is not a good thing. As Orange friend "Zhu Er" said, the old fishermen in Qiandao Lake used to catch yellowtail and bigeye bream, which are also the most delicious. But they have become difficult to catch in the past two years. You can see many small sunfish and tilapia on the shore.

Wang Yuxi, director of the Fisheries Institute of the Hangzhou Academy of Agricultural Sciences, said that in Qiandao Lake, the most troublesome thing is the young sunfish. The big sunfish have fewer bones and are suitable for the elderly and children to eat. They are caught away, and the remaining young fish have no economic value, so they are left. As a result, batches of young fish grow into big fish, and there are more and more of them.

Expert: The invasion of alien species is actually an ecological and environmental problem

So, is the sunfish considered a nationally high-risk invasive species? Are all alien species harmful?

Gu Dangen, an expert on alien species research at the Pearl River Fisheries Research Institute, said that this cannot be generalized.

"Not all foreign fish are bad. For the purpose of aquaculture, my country has introduced many foreign fish. Largemouth bass, channel catfish, etc. are all of economic value, and have played an important role in fishery production and increasing fishermen's income. The sunfish we are discussing today is also a species. There are still many places where it is being cultivated, and it also has considerable economic value. However, on the other hand, due to the escape of cultivation caused by non-standard cultivation mode and artificial release, green sunfish and bluegill sunfish have caused harm in local waters. However, compared with foreign invasive populations such as Qi's tilapia and leopard wing armored catfish, the distribution and harm range of sunfish is smaller, and the risk level is relatively low. However, in order to avoid the proliferation of sunfish, scientific control is also very necessary while doing a good job in cultivation management."

However, Gu Dangen mentioned tilapia, which is very similar to sunfish. Tilapia was also introduced for breeding purposes and there are multiple species. Tilapia is currently the most farmed foreign fish in my country. It is also the most widely distributed and most influential foreign fish in natural waters. Not only my country, but most tropical and subtropical regions around the world are threatened by the invasion of tilapia.

How did this happen? A typical example is the invasive alien species, the Tilapia chinensis, which was introduced from Thailand in 1978. Due to its small size and slow growth rate, it was soon eliminated from aquaculture after its introduction. However, its low-temperature resistance and strong reproductive capacity promoted its invasion and spread in natural waters, while the vacant ecological niche caused by the reduction of local biodiversity provided good conditions for the outbreak of the Tilapia population.

It is just like the saying goes: If you try to plant flowers, they may not bloom; but if you plant willows by accident, they may grow into a shade.

At present, the Qi's tilapia has spread to many regions including Hunan, Jiangxi, Hubei, Sichuan, etc., and continues to spread and spread, posing a huge risk.

Gu Dangen said that the invasion of alien fish seems to be an agricultural industry problem, but in fact it is more of an ecological environment problem. The introduction of aquatic species only provides the possibility of invasion. The deterioration of the water ecological environment and the reduction of biodiversity caused by overfishing, human release and abandonment, and other human interference factors such as dam construction are the key factors for the successful invasion and large-scale spread of these highly adaptable species.

The control of such invasive fish is a systematic project that requires the collective participation of the government, scientists and the public.

In addition to breeding, there are quite a few alien species in the domestic ornamental fish population. According to incomplete statistics, there are more than 400 species of alien ornamental fish introduced into China. The problem of alien species invasion caused by random release is also very common, and the alligator gar is a typical example. Therefore, people who raise ornamental fish should not release them at will.

Han Chenke, reporter of Orange Interactive