Small freshwater fish are often forgotten by the general public. Michael Edmondstone of SHOAL believes aquarists are key for spreading the word about the threatened small fish.
We can describe freshwater fishes as the “forgotten vertebrates.” Despite representing more than half of all fish species, they rarely feature in mainstream conservation. And even within this overlooked world, it’s still the large, charismatic animals that draw attention. People often picture salmon leaping upriver, giant catfish, or so-called “river monsters" when they think of freshwater conservation.
Tiny fishes are almost entirely absent from the spotlight. Yet, these small-bodied fishes play outsized ecological roles. They live in habitats that are rarely surveyed, act as sensitive indicators of water quality, and support food webs from the bottom up. Plus, many of them, as the fishkeeping community will know, are astonishingly beautiful, behaviourally rich, or simply bizarre.
SHOAL’s report on tiny fishes aims to shift attention onto these biologically fascinating miniature marvels. They are in urgent need of recognition.
Did you know, SHOAL’s Priority Fishes list features 295 fishes that are under 4cm (1.6").
Somphongs rasbora are Critically Endangered and reach just 3cm (1.2") Photo by Alex Bell.
Why tiny fishes are overlooked
Many miniature species slip through the cracks of science and conservation. Standard sampling methods tend to miss these tiny fishes, allowing entire communities to go unrecorded. Meanwhile others have historically been dismissed as juveniles of larger species.
But their neglect is also perceptual. Humans often see tiny fishes as inconsequential compared to the larger species tied to food security or cultural symbolism. Plus, their short lifespans, specialised habitats and small ranges make them extremely sensitive to pollution, habitat loss and hydrological change. This all means that they are among the first to disappear when ecosystems decline.
The tiny and see through Danionella cerebrum are easily overlooked. All photo by Shutterstock unless otherwise stated.
Where tiny fishes thrive, water quality is almost always good. Lose them, and the decline of the wider ecosystem usually follows soon after.
Notable Tiny Species
Ruby rasbora (Paedocypris progenetica) – Near Threatened
One of the world’s smallest vertebrates, reaching just over 10mm, this Sumatra native lives in acidic peat swamps. Long overlooked as considered the juvenile of another cyprinid, it highlights how much biodiversity survives out of sight. You may also see it called the Indonesian superdwarf fish.
Micro glassfish (Danionella cerebrum and Danionella translucida) – Data Deficient and Least Concern
Danionella translucida and D. cerebrum are extraordinary for their transparency. The latter, with a see-through head, has become a top neuroscience model organism. Thus proving that these tiny fishes can have unexpected key roles to play outside their natural environment.
The ‘penis throat’ fish (Neostethus spp.) – Of the 12 species, six are Data Deficient, two are Least Concern, two are Endangered, and two are Critically Endangered
A Southeast Asian genus famed for its unusual reproductive anatomy. Several species are Endangered or Critically Endangered and feature on SHOAL’s Priority Fishes list.
Banded Neolebias (Neolebias lozii) – Critically Endangered
This 2cm (0.8”) characin from Zambia’s Barotse floodplain survives only in a handful of vegetated channels. These channels are at risk from drainage and changes to flood patterns. A stark reminder of how easily entire worlds of specialised tiny fishes can vanish.
Coral red pencilfish (Nannostomus mortenthaleri) – Critically Endangered
Much loved in the hobby for its intense red fins, this Peruvian species is found only in one small tributary of the Rio Nanay. Harvesting pressure and habitat change place it among South America’s most threatened miniature fishes.
Gateways to Hidden Habitats
Tiny fishes draw us into ecosystems we rarely think about: peat swamp forests, artesian springs, ephemeral forest pools, seepages and shaded backwaters. Protecting these species means protecting the specialised microhabitats they depend on. Often these are exactly the places most vulnerable to drainage, pollution, invasive species, or other anthropogenic threats.
Why Aquarists Matter
The aquarium community has long valued small and nano-sized fishes, making hobbyists uniquely placed to champion their conservation. Projects such as the Parosphromenus Project show how enthusiasts can help document species, support breeding initiatives and raise awareness of their wild habitats.
With many tiny species now categorised as conservation priorities through SHOAL’s 1,000 Fishes initiative, the hobby has an important role in keeping their stories alive.
Tiny fishes with a huge message
Tiny fishes represent biodiversity that could easily disappear unnoticed. They are ecological linchpins and living testaments to evolution’s creativity. Most importantly, they remind us that conservation begins with noticing. Look closely at a tiny fish, and you discover an entire hidden world worth protecting.
Spend a moment and read SHOAL’s Tiny Fishes report, and give these tiny fishes the attention they deserve. SHOAL dive deep into 10 incredibly different species, speaking with some of the researchers working alongside them. Subscribe to their newsletter to keep up to date with their freshwater conservation efforts.