November, a time of mourning and remembrance of the dead common to many cultures, is upon us. It’s a good time to remember the recently extinct fish species, as well as the aquatic mammals that have become similar to them due to convergence (and subjected to the same pressures): whales and dolphins. The International Union for Conservation of Nature (IUCN), as of September 2016, listed 65 species of fish definitely extinct, 87 probably extinct, and finally another 6 no longer found in the wild. Our century brought the first officially recognized extinction of an oceanic fish – the unnamed Tasmanian Sympterichthys unipennis and the freshwater dolphin – the Chinese baiji Lipotes vexillifer.
Species disappear like camphor. Problems multiply like rabbits
Updating the 2016 data, showing the status as of mid-October 2023, was not easy. Specialized databases tend to be inaccessible. And common IUCN listings (and Wikipedia, which draws from them) are not precise enough. A species listed as “definitely extinct” on one list, is listed as “extinct in the wild” or “critically endangered” on other sub-lists.
Another problem is sometimes taxonomy, or more specifically, recognizing what was a proper species and what was merely a local race or morph. This is a weighty problem in the case of certain fishes, in which either larval stages, males and females, or particular categories of males, using different reproductive strategies, are sometimes so dissimilar to their fellows that they are classified into separate species, or even genera and families. Examples of such problems included:
- recognizing the leptocephalus as some strange ocean fish, rather than the larvae of European and American eels that it turned out to be;
- The recognition for centuries of parr and smolt as small, freshwater fish of their own species and kind, suitable at best for fertilizing fields and herding livestock, rather than the juvenile stages of salmon, sea trout and trout that they actually are;
- Recognizing “jacks” (jacks) and “hooknose” (hooks) as fish of different species, even though they are male Pacific salmon using different reproductive strategies.
Of course, there have also been reverse cases. For example, parasitic worms sometimes found in eels were taken for their fetuses/larvae, analogous to sharks and rays. A marine perch fish, the eelfish Zoarces viviparus, was taken for either a female European eel or a hybrid between eel and burbot or cod.
A third challenge with this type of analysis is sometimes the accepted borders and number of continents/parts of the world, which makes it difficult to compare statistics for different regions. Australia is sometimes discussed together with New Zealand (due to cultural and political proximity), other times together with Papua New Guinea (due to geographic proximity, though not necessarily biogeographic), but omitting data for French New Caledonia. It is also surprising that according to some English-speaking naturalists, not only the Caucasus, but also the Carpathians lie in Asia.
Let’s take a closer look at the losses of each continent. Completely extinct fish species in the 20th century:
- 9 species of European fish (pest pig Chondrostoma scodronse, Techyrgolian stickleback Gasterosteus crenobiontus, Neuchatel’s pilchard Salvelinus neocomus and 6 species of Coregonus spp. whitefish);
- 25 species of Asian fish (lost shark Carcharhinus obsoletus, Jilong carp Cyprinus yilongensis, Fedchenki sturgeon Acipenser fedtschnkoi, a dozen species of Barbodes barbel, 2 species of Tristramella pygmy);
- At least 36 species of North American fish (primarily endemic vendace, but also individual representatives of Cottus cephalopods, Moxostoma tenderos, Etheostoma etheostoma and Zander zander);
- At least 3 species of South American fish(Azurina eupalama from the Galapagos, Orestias cuvieri from Titicaca, and Rhizosomichthys totae from Lake Tota);
- At least 4 species of African fish;
- At least 2 species of Madagascar fish (such as the Ptychochromoides pygmy);
- at least 2 species of Wallacean fish (Australia, New Guinea, Tasmania and New Zealand) (“New Zealand grayling” Prototroctes oxyrhynchus and the first officially declared extinct high seas fish Sympterichthys unipennis) [1-5].
Are extinct fish species the tip of the iceberg?
Extinct fish species are probably more than those listed above. Among others, the following have almost certainly disappeared from European waters. Knipowitchia camelii Knipowitchia camelii from the Danube delta and Alosa vistonica Thracian allosa from Greece’s Lake Vistonida. The fauna of Asia may have been depleted by another 22 species (including the endemic carp of China). Both in the great lakes of Africa and in private aquariums, there are no further 45 species of Haplochromis pygids.
Not only have the charismatic sturgeon Acipenseridae, long rare, Atlantic salmon Salmo salar and whiting Stenodus leucichthys become completely dependent on stocking, but they were also common back in the early 20th century. Anguilla anguilla eels and Silurus glanis catfish. We have yet to see a decline in the latter, although reading through the labels of canned goods reveals an increasingly widespread replacement with Clarias glariepinus arthropods.
Already extinct in the current, 21st century, are the baiji dolphin , Chinese paddlefish Psephurus gladius, Yangtze sturgeon (Dabry’s j.) Acipenser dabryanus and the Atlasian Labeobarbus reinii [1-5].
In captivity alone, there are at least eight species of North American fish and dozens from Africa and Asia, such as. Kawamura salmon (kunimazu Oncorhynchus kawamurae). Only one species from Tasmania – Galaxias pedderensis Peddera galaxis – has survived in replacement sites. The list of extinct fish species, unfortunately, continues to grow.
Small is beautiful, but big can do more
Even a cursory analysis of the collected data makes it possible to discern certain patterns of extinction in the 20th and 21st centuries. They are fading, first and foremost:
- Endemic forms, with small ranges, limited to single “habitat islands” (individual lakes, springs, river basins);
- taxa simultaneously subjected to many different forms of human pressure and invasive alien species (e.g.: cichlids from tectonic lakes of Africa harvested for aquariums and eaten by the “Nile perch” or whitetail, which has been overfished and the surviving individuals often interbreed with the more common nelma);
- Those less prolific than other representatives of their cluster.
Endemics included both the aforementioned cichlids of the great lakes of the Black Continent, the streams of Madagascar and the headwaters of Central America, the barbel of Southeast Asia, as well as a number of carp and whitefish, single species of aloz, sticklebacks or steelhead, limited in occurrence to selected lakes, as well as knipoviye known only from the Danube delta.
The second pattern of extinction is known, for example, from Lake Victoria, where as a result of aquarium harvesting, overfishing by fishermen, and the introduction of the Nile lates (“Victoria perch”) Lates niloticus in the 1950s. In the 1970s. there has been a rapid disappearance of dozens (perhaps even hundreds) of endemic fish species, as described by Tijs Goldschmidt in his book “Darwin’s Dream Lake. Drama in Lake Victoria.”
A great example of the simultaneous action of a number of factors can be the construction of dams combined with the introduction of alien species. Such were the reasons for the extinction of the “New Zealand grayling” (unrelated to the true grayling of the northern hemisphere), which was almost completely wiped out by the construction of hydroelectric power plants and stocking with trout. It narrowly missed sharing its fate with Pedder’s galax, similar in appearance to our salmonids and in direction of migration to eels.
In the southern part of the globe, a similar fate may await the two-tailed merganser (barramundi) Neoceratodus forsteri, which is threatened by the baffling of watercourses and water abstraction for agricultural irrigation. Apparently, there are still plenty of them, but the longevity of these animals and their natural tendency to reproduce on a not-so-regular basis mean that we may miss the moment when they stop having young. And then they will just die out [2, 6, 7].
We also do not know what will be the fate of the Baikal Commephorus golomiana. Their endemic range plus peculiar reproductive biology makes them quite vulnerable to lake poisoning and alien species encroachment. The days of exporting their fat en masse to China may also return, following the decline of sunflower crops in Ukraine.
The exception proves the rule
Contrary to appearances, the case of the Tasmanian handfish Sympterichthys unipennis (syn. S. verrucosus) also fits perfectly into the above trends. While this fish is considered oceanic, it was naturally confined to isolated microhabitats within what is known as the “oceanic” area. D’Entrecasteaux Canal, between Tasmania and Bruny Island. The entire family Brachionichthyidae, to which S. unipennis belongs, brings together endemics of Australia’s eastern seas with a lifestyle unusual for most fish: walking on the bottom and giving birth to a few young instead of laying thousands of eggs.
This contributes to a lack of dispersal, and consequently to the formation of isolated populations that undergo speciation into separate species. Sympterichthys unipennis may become a flagship example of a species wiped out completely involuntarily as a result of the extraction of rocks and silt from the seabed, or as bycatch, during clam fishing [8-10].
Offspring care or other K-strategy mechanisms (e.g.: egg-laying into the mantle of a live clam in our roselle Rhodeus amarus, giving birth to only a few, but relatively independent young from the start in many sharks and rays) may be as effective on a scale of millions of years as r-strategies with millions of eggs per female each year. But what happens when a competitor with the same strategy but lower oxygen or nutritional requirements appears in the environment? We see this, moreover, in the case of our catfish Silurus glanis and the American catfish Ictalurus or the native gobies and their Caspian-Black Sea competitors.
Why are extinct fish species such a large group?
Baiji and the “dinosaurs of the fish world,” the sturgeon and paddlefish of the Yangtze River basin, are extinct fish species of the past few years. The intensified efforts of the entire scientific world and all the power – scientific, financial and police – of totalitarian People’s China did not help. Their extinction contrasts with successful efforts to save the giant panda, tiger or milo deer. Apparently, it is easier to protect terrestrial species. Probably because they are more familiar to us. The principle may also work: what comes from the eyes, comes from the heart.
Using the example of baiji, you can see how human pressures have literally changed in a few, several years. While during the Great Tiger Leap they were killed for hunger, for skins, or as part of the fight against superstition/one-child policy, in the 1970s they were killed for hunger. fell victim to bycatch, in the 1990s. beating fish with electricity, and in the 21st century. They were hit by the construction of the Three Gorges Dam [5, 11-13].
What good is an absolute ban on poaching while condoning sewage dumping and the risk of colliding with ships, not to mention dredging and concreting the bottom? What good does it do to rebuild a population of potential prey when the survivors of dolphins – animals that are nearly blind but masterfully use echolocation – are literally stunned by the underwater noise of boat propellers?
There is currently a lot of buzz about the drought in the Amazon and the threats it poses to the freshwater dolphins there. One hears little new about their brethren from the great rivers of India. Wiser by the example of Lipotes vexilifer we can still save them. Perhaps. If we act immediately [5, 11-13].
Fish and cetaceans are still less threatened with extinction than other aquatic organisms, especially amphibians and freshwater bivalves of the glochidium stage (scaphopods and pearl mussels). However, it should not be forgotten that the ecosystem is an interconnected system. This is brilliantly illustrated, for example, by the interaction of domestic fish and mussels with their new, invasive “colleagues.” The glochidia of the giant Chinese rattlesnake, which, according to the doyen of Polish malacology, had no chance of establishing itself in Poland, sensitize their Polish hosts so strongly that the latter either otorbate or “shed” the glochidia. The result? Native clams are dying out sooner than native fish.
In the article, I used, among other things. From the works:
- Kottelat M. (2013): The Fishes of the Inland Waters of Southeast Asia: A Catalogue and Core Bibliography of the Fishes Known to Occur in Freshwaters, Mangroves and Estuaries. The Raffles Bulletin of Zoology, 2013, Supplement 27: 1-663.
- Lee F., Perry G. L. W. (2019). Assessing the role of off-take and source-sink dynamics in the extinction of the amphidromous New Zealand grayling (Prototroctes oxyrhynchus). Freshwater Biology. 64 (10): 1747-1754.
- Miller R. R., Williams J. D., Williams J. E. (1989). Extinctions of North American Fishes During the Past Century. Fisheries. 14 (6): 30.
- Sayer C.A., Máiz-Tomé L., Darwall W.R.T. (2018). Freshwater biodiversity in the Lake Victoria Basin: Guidance for species conservation, site protection, climate resilience and sustainable livelihoods. Cambridge, UK and Gland, Switzerland: IUCN.
- Stiassny M., Sparks J. S. (2006). Phylogeny and Taxonomic Revision of the Endemic Malagasy Genus Ptychochromis (Teleostei: Cichlidae), with the Description of Five New Species and a Diagnosis for Katria, a New Genus. American Museum Novitates. 3535.
- Flecker A. S., Townsend C. R. (1994). Community-Wide Consequences of Trout Introduction in New Zealand Streams. Ecological Applications. 4 (4): 798-807.
- Kaminskas S. (2020). Alien pathogens and parasites impacting native freshwater fish of southern Australia: a scientific and historical review. Australian Zoologist. 41 (4): 696-730.
- IUCN SSC Standards and Petitions Committee (2021). Sympterichthys unipennis. IUCN Red List of Threatened Species. 2021: e.T123423283A207621852.
- Last P.R., Edgar G., Stuart-Smith R. (2020). Sympterichthys unipennis. IUCN Red List of Threatened Species. 2020: e.T123423283A123424374.
- Shiffman D. (2020). Smooth Handfish Extinction Marks a Sad Milestone. Scientific American. 323 (1): 14.
- Reeves R. R., Smith B. D., Crespo E. A., Notarbartolo di Sciara G., eds. (2003). Dolphins, Whales and Porpoises: 2002-2010 Conservation Action Plan for the World’s Cetaceans.
- Smith B.D., Wang D., Braulik G.T., Reeves R., Zhou K., Barlow J., Pitman R.L. (2017). Lipotes vexillifer. IUCN Red List of Threatened Species. 2017: e.T12119A50362206.
- Turvey S. T., Pitman R. L., Taylor B. L., Barlow J., Akamatsu T., Barrett L. A., Zhao X., Reeves R. R., Stewert B. S., Wang K., Wei Z., Zhang X., Pusser L. T., Richlen M., Brandon J. R., Wang D. (2007). First human-caused extinction of a cetacean species? Biology Letters. Royal Society Publishing. 3 (5): 537-540.
Photo source: Wikipedia/By Roland Seitre, CC BY-SA 3.0,