In North America, salmo trutta is a very common trout, this cold-water fish is rich in nutrients, tender meat, delicious taste, by many consumers sought after. In the European market, brown trout is more popular – the North Atlantic was originally the "home" of brown trout, and Norway and Russia have taken advantage of the geographical advantage and are well-known brown trout "big producers".
Salmo trutta
In terms of body size, brown trout is a large and medium-sized fish, adult individuals can grow up to 140 cm, weigh up to 20 kg, but such giant brown trout is very rare in the wild. In large lakes, brown trout are generally between 40 and 80 cm in size, while in narrow streams, small brown trout of about 20 cm are more common.
For Lua players, the brown trout is a very tempting sport fishing species. In September 2009, American game anglers successfully caught a 18.8 kg brown trout in the Manisti River, setting a Michigan record. In Europe, sport fishing for brown trout is also a popular entertainment project, and the popularity remains high all year round. Whether it is food or sport fishing, the huge economic value of brown trout has made "businessmen" around the world want to move.
Record-breaking giant brown trout
Beginning in the 1860s, brown trout was introduced around the world as an excellent cultured species. Today, with the exception of Antarctica, wild brown trout populations can be found on every continent of the world, most of which have escaped from farms.
The first country to introduce brown trout was Australia, but the most "successful" introduction was in the United States. In 1883, Fishery experts in the United States imported a batch of fertilized eggs of brown trout from Germany, which were artificially hatched and carefully bred by professionals, and the results were very successful.
Brown trout at different times (significantly different body color during the seawater and freshwater phases)
In April of the following year, the U.S. Fish Commission released 4,900 trout seedlings into Michigan's rivers, the first time brown trout had been released into natural U.S. waters. Over the next dozen years, the brown trout expanded, which catered to American psychological expectations.
The water quality conditions around the western river network and the Great Lakes in the United States are very suitable for the growth and reproduction of brown trout, and brown trout from Europe soon succeeded in "ascending" and became one of the most common cold-water fish in the United States. By 1900, the brown trout had expanded to 38 states in the United States, and the "industrial cake" brought by the fish was getting bigger and bigger.
Range of brown trout in the United States
In the United States, trout farming is a hot "business" – as early as 1997, 18 states in the United States carried out large-scale trout farming, with a total output value of more than 77 million US dollars, the momentum of catfish (catfish) and California perch (aka largemouth bass). At the commercial fish stage, most fresh trout are sold to local restaurants and hotels, while supermarkets prefer to source frozen trout meat. In addition, a considerable part of the trout is dedicated to the fishing and recreation of American residents, and the resulting tourism revenue is also considerable.
Cage culture of trout
However, the expansion of the population of the brown trout also brings many ecological problems. Under natural conditions, brown trout usually feed on invertebrates, but also feed on other fish, frogs and aquatic insects. Even more surprising is that some large brown trout sometimes jump out of the water to prey on birds and even cannibalize when hungry. Ecologists in the United States point out that the introduction of brown trout has changed the food chain and nutritional relationships of rivers in the United States, and the resulting competitive pressure is gradually reducing the number of brook trout in the United States.
In Australia and New Zealand, the introduction of brown trout has also led to a rapid decline in native fish populations, and some species have even become locally extinct. In New Zealand in particular, brown trout have become almost the top predators in natural rivers, not only resulting in a decrease in the abundance of aquatic life, but even changing the survival strategies of some invertebrates (after the introduction of brown trout, the local ephemerals gradually developed a nocturnal foraging habit, which is precisely to avoid the brown trout's predation).
In China's Tibet, Qinghai and other places, the wild population of brown trout has begun to take shape, although there has been no relevant negative reports, but with the continuous expansion of the population size, brown trout is also likely to cause irreversible harm to China's plateau fish.
From the perspective of ecological habits, the brown trout populations in Qinghai and Tibet are also worthy of vigilance.
First of all, brown trout grows very quickly and has an early sexual maturity time. In Tibet's Yadong River, brown trout can grow to 20 centimeters in 2 years, and the brown trout is already capable of reproduction (in fact, the brown trout is already reproductive at about 50 grams). In the same waters, native cold-water fish such as split-bellied fish and plateau loach develop much more slowly. Therefore, in the competition with brown trout, native highland fish are often at a disadvantage and even fall prey to the former.
Brown trout have a strong jumping ability and escape from farms occurs from time to time
In addition, the brown trout's ability to adapt to unfamiliar environments is also excellent. 13,000 years ago, the brown trout in the Irish region of the United Kingdom was separated into different environments due to geographical changes, and after a long evolution, these brown trout formed different ecological types, such as "stomach trout", "blacktip trout" and so on. So far, there are more than 50 documented brown trout ecological types, which is enough to be amazing.
Today, brown trout is one of the most common fish species in the Yadong River, while the local indigenous fish have quietly "faded away", which is a situation that makes people lament.
But then again, the introduction of trout from China is not just a brown trout, another common species is the rainbow trout (Oncorhynchus mykiss). In China, many people may not know about the brown trout, but they have basically heard of the rainbow trout – this fish has been "popular" many times because of the "fake salmon" incident, and it has also attracted a lot of "stains".
Global rainbow trout production (in tonnes)
Compared with the brown trout, the ecological threat of the rainbow trout is even greater. Rainbow trout is generally no more than 10 kilograms in size, which is not very large compared to brown trout, but this fish will frantically devour the eggs of other fish, including brown trout, mountain white salmon, red spot salmon and other economic fish.
In addition, rainbow trout are also very greedy, eating almost any prey they can catch, even corpses and carrion. In China, rainbow trout is the first trout to be introduced, and after more than 30 years of artificial breeding, it has gradually formed a number of cultured species such as triploid rainbow trout, golden trout, and all-female rainbow trout.
Rainbow trout (Oncorhynchus mykiss )
Nowadays, the cultivation of rainbow trout has been promoted to 23 provinces and autonomous regions in China, with an annual output of more than 5,000 tons. In the 1990s alone, the freshwater rainbow trout in Longyangxia, Qinghai Province, exceeded 15,000 kilograms. Today, Longyang Gorge has launched the sign of "Plateau Rainbow Trout" and has become an important cold-water fish production base in the country.
It is undeniable that brown trout and rainbow trout are both rare aquatic treasures and "ecological killers". How to make good use of the two major cold-water fish species, brown trout and rainbow trout, and minimize the ecological impact while commercial development, is indeed a topic worthy of serious consideration.
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#Rainbow Trout ##Protecting Ecology ##物种入侵 #