It took three biologists to pull a 109kg fish from the Detroit River in Michigan last month. The monster sturgeon, nearly 2.1 meters long, caught and released by the Alpena Fish and Wildlife Protection Agency, may be over 100 years old. It’s certainly an impressive catch, but it’s not the largest freshwater fish in the world.
The fish of the Detroit River is the lake sturgeon (Acipenser fulvescens), and although considered one of the largest ever caught in the United States, much larger fish swim in rivers around the world. According to the US Geological Survey, the largest freshwater fish on the planet is the beluga (Huso Huso), which lives between Europe and Asia in the Black, Azov and Caspian Seas, as well as in the rivers that feed them.
It can reach a maximum length of over 8 mi and weigh up to 2.2 tons, according to WWF. Beluga stands at the top of the food chain, eating fish such as roach, carp, as well as waterfowl and even seals, according to the International Union for Conservation of Nature (IUCN).
Belugas can live for over 100 years like lake sturgeon, which gives them plenty of time to grow. “If you live long, you will have plenty of time to eat,” Fedra Dukakis, a fisheries policy analyst at the National Oceanic and Atmospheric Administration (NOAA), told Live Science.
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Sturgeons have been around for over 250 million years and have even lived with dinosaurs. Beluga is the largest of the 27 living species of sturgeon and paddlefish.
Apart from their long life, it is difficult to say why belugas grow so large. Larger sturgeon species likely had greater reproductive success, possibly because females can produce more eggs than females of smaller fish. Their sheer size can also help them catch prey and survive when interacting with predators, according to Leonardo Congiu, assistant professor of ecology at the University of Padua in Italy.
However, today’s beluga may not reach more than 7m in length. “I don’t think there is a beluga of this size,” Kongiu told Live Science by email. “This species is under a lot of poaching pressure, and probably all the large animals have been caught.”
Kongiu and colleagues published an article on the distribution and genetic diversity of beluga populations in January 2021 in the journal Diversity and Distributions. They are aiming to bring fish back to Italian rivers after it has become extinct locally due to overfishing and dam construction in the country.
Sturgeon belugas are listed in the IUCN Red List of Endangered Species, in the category of the most endangered species. Adult females are prized for their fish roe, which is sold at over US $ 8,000 / kg), according to the IUCN.
Dukakis, who is also co-chair of the IUCN Sturgeon Specialist Group, believes there may be belugas over 23 feet tall, but there will be significant rewards for their heads. “An old female that has reached this length can be loaded with eggs, and poaching can be very, very expensive for the continued existence of the species.”
Caviar from sustainable farms is currently available, but Dukakis explained that even if maximum protection measures are taken for the wild beluga, it will take a long time for juveniles to mature and reach maximum length.
The title of the largest growing sturgeon today may belong to the white sturgeon (Acipenser transmontanus), the largest sturgeon in the United States. In fact, people are likely to be more likely to see a larger white sturgeon than a beluga, simply because the white sturgeon is probably under better protection, ”Dukakis said.
According to the IUCN, at the moment, the white sturgeon is not threatened with extinction, and its population is stable. However, like almost all sturgeon species, they are threatened by the construction of dams. The dams prevent sturgeons from swimming upstream to reach their spawning grounds, Dukakis said, and also change the ecological conditions in the rivers in which the sturgeon lives.
Beluga and white sturgeon are called freshwater fish because they are born in fresh water and use it for breeding, but they also live in the marine environment. Dukakis preferred to refer to them as freshwater dependent fish to distinguish them from species that spend their entire life in freshwater.
What about the largest fish that only lives in fresh water? This record belongs to the giant Mekong catfish (Pangasianodon gigas), which lives in the Mekong River in Southeast Asia. These catfish can grow up to 3 m in length and have previously been caught from 293 kg. Like the beluga, the IUCN considers this fish to be endangered due to dams and overfishing, writes Live Science.
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