According to a report ‘New Species 2021’ published by the conservation organization Shoal, scientists discovered over 200 freshwater fish species (212 to be more precise) in 2021.

Scientists are celebrating this discovery of freshwater fish species. These species include a blind eel which was found in the lands of a school for blind children and a type of fish named Wolverine that has hidden weapons and defense mechanisms.


The report published by the conservation organization Shoal shows the world’s most divergent and undervalued freshwater species that are remarkable. The report suggests there might be much more species still to be discovered in the world’s lakes, rivers, and wetlands.

“It’s fascinating that over 200 new freshwater fish species can be described in just a single year,” said Harmony Patricio, Shoal’s conservation program manager. “You might see this level of new discovery for organisms like plants or insects, but not really for vertebrates.

“It means there are still hundreds and hundreds more freshwater fish out there in the world that scientists don’t know about yet,” she said. “Also, many of the newly described species have pretty unique and unexpected traits.”

Danionella cerebrum, about the size of a thumbnail, is used in neuroscience research because of its visible brain cavity. Credit: Ralf Britz


Wolverine pleco’s (Hopliancistrus wolverine) hidden weapons mechanism is one of the most startling and unexpected physical characteristics scientists found. The Wolverine pleco, which earned it an X-Men character-inspired name, has strong lateral curved spikes called odontodes hidden under the gill covers that can be extended to punch anything that tries to mess with them.


“Other related species in the same family, even those with big spines, aren’t known to demonstrate such behavior. The researchers who described this species ended up with quite a few finger injuries while collecting specimens from the wild,” Patricio said.


Other discoveries include the bright red Mumbai blind eel (Rakthamichthys Mumba), which has no fins, scales, or even eyes. This species was found at the bottom of a well on the grounds of a school for blind children. Another one is a tiny, translucent Danionella cerebrum, discovered in southern Myanmar and just a bit larger than a thumbnail. Other findings are the colorful Kijimuna and Bunagaya gobies (Lentipes kijimuna and Lentipes bunagaya) in southern Japan, named after woodland spirits in Okinawan folklore.


These remarkable 212 discoveries offer new possibilities for scientists to boost their understanding of freshwater species. These new species will help scientists to understand them including their anatomy, evolution, and the connections between other creatures and their habitats.

For instance, the male Danionella cerebrum has made the researchers curious to know more about its ability to make a drumming sound, most likely by tapping a thin strip of cartilage on its swim bladder, like a drumstick. Scientists think this might be a relatively complex and unusual form of communication for such a tiny creature.

According to the standard reference book ‘Eschmeyer’s Catalog of Fishes, there are at least 18,267 species of freshwater fish.


“We know that 80 species of freshwater fish have gone extinct in modern times, while there are usually around 150-200 or more new species discovered in an average year,” said Patricio. “But population levels of many freshwater fish have declined massively over the past 50-plus years.

“There’s a whole suite of factors that has led to their decline, but the primary causes are impacts from invasive species, pollution, overfishing and habitat loss, and degradation.”.

“Hopefully,” she said, “they’ll be motivated to support conservation efforts and encourage their governments to do more.”


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