Living at 12,000 feet – Lake Titicaca “scrotum” frog adapted to the high life

Entirely aquatic and one of the largest frogs on the planet, growing up to the size of a salad plate, the Lake Titicaca water frog also makes one of the stranger fashion statements in the amphibian world. Its excessive skin folds, which look like someone put its skin through a taffy-puller and then sewed the result back on, have earned it the whimsical Latin name of Telmatobius culeus – “aquatic scrotum.”

The scrotum frog’s bizarre outfit is actually the perfect adaptation to the cold waters of its high-altitude home. The bottom-dwelling frog is only found in Lake Titicaca, often called the highest navigable lake in the world, sandwiched between Peru and Bolivia. The frog is entirely aquatic, living in the reed beds of the lake and its rivers. Avoiding the oxygen-depleted air, its ornate skin folds and abundance of capillaries allow it to absorb oxygen directly from the saturated water, making up for its tiny lung size and allowing it to stay permanently below the surface – which protects it from the high levels of ultraviolet radiation found in the area. It also benefits from a high number of small red blood cells, which efficiently deliver oxygen and remove carbon dioxide from its body tissues.

Illustration by P. Roetter, Bulletin of the Museum of Comparative Zoology

Illustration by P. Roetter, Bulletin of the Museum of Comparative Zoology

The oddball frog has fascinated people for centuries. Lake Titicaca frogs were believed to have special powers, particularly in bringing  rain: once carried in a ceramic pot to a hillside, the frogs would call in distress, which supposedly sounded to the gods like a plea for rain. Once the downpour began, the pot would overflow and the sacred animals would escape back to the lake. The frog also captured the imagination of its 1876 European discoverer, S.W. Garman – as witnessed by his choice of a name. Jacques Cousteau, searching Lake Titicaca for Inca treasure in the 1970s, was equally enthralled, reporting “thousands of millions” of the frogs, some almost 20 inches long.

These days, such giants are unlikely to be seen. Aside from global threats to amphibians such as the chytrid fungus and invasive species, in this case a trout that preys on its tadpoles, the Lake Titicaca water frog suffers from over-popularity. It is a favorite menu item at tourist restaurants around the lake, and is also taken to Lima markets – where it’s sold as an aphrodisiac. The frogs are skinned and then blended with water, maca (a local root vegetable) and honey into a juice, thought to be the cure for several ailments, including impotence. It is also collected as a pet or curiosity, while pollution, habitat loss, and overfishing of its main prey, the small fish known locally as ipsi, could also be pushing the critically endangered frog towards extinction.

In response, captive breeding programs have been established for the giant amphibians, both around Lake Titicaca and internationally. One possible plan is to farm the frogs for consumption, taking the pressure off those left in the wild, although this could subject the small population to increased risk of disease from large, densely-kept captive populations. Scientists from both Peru and Bolivia are studying the frog, to assess its ecology and feeding habits as a base for captive breeding.

ARKive video – Lake Titicaca frog

Axolotl (Ambystoma mexicanum)

"Ambystoma mexicanum 1" by Stan Shebs - CC-BY-SA-3.0

“Ambystoma mexicanum 1” by Stan Shebs – CC-BY-SA-3.0

Our newest addition to the cabinet comes by special reader request, collected by Cecilia Larraga! Its name, from the Aztec Nahuatl language, means “water monster,” and it’s also known as the Mexican walking fish, but the axolotl is neither a fish, nor can it survive out of water. Its unique lifestyle and almost non-existent range (not to mention its ability to regenerate) make it a curious creature, to say the least!

I don’t want to grow up

Unlike most salamanders, axolotls never go through metamorphosis. With the odd exception, they stay in their larval stage for their entire lives, a condition known as “neoteny.” This is partially what gives the species its bizarre look, since axolotls keep their tadpole dorsal fin, as well as the feathery external gills that stick out like a strange headress. Since they never develop air-breathing lungs, axolotls spend their entire lives underwater. Staying in tadpole stage doesn’t prevent axolotls from reproducing, however; they mate underwater and the females lay their eggs on plants and other available surfaces.

They’re normally black or brown, but pink or white albinos are commonly found in captivity – and sadly, captivity is almost the only place where the fascinating creatures still exist these days. Found only in the former Lake Xochimilco complex in Mexico City, the axolotl has taken a beating as the city grows. Lake Xochimilco and Lake Chalco have been gradually drained to reduce flooding risk and make room for expansion; Chalco has totally disappeared, and the axolotl now clings on in a few remaining canals and small lakes.

Ambystoma mexicanum Photo © Biopix: N Sloth

Ambystoma mexicanum by Biopix: N Sloth – CC-BY-NC

According to research by Dr Luis Zambrano of the National Autonomous University of Mexico, the critically-endangered species lives in only six isolated parts of the Xochimilco system, usually near springs that still have clear, fresh water. Zambrano’s team says there may be only 700 to 1200 individuals left in the wild. Water pollution is another reason the population has crashed; it also has to deal with competition from introduced fish like tilapia and carp. Unfortunately, using reintroductions to boost the wild population might be dangerous, since it would risk introducing the chytrid fungus currently wreaking havoc in amphibians worldwide. However, the axolotl is widespread in captivity – it’s extremely popular both as an aquarium pet, and as a subject of scientific research.

Hey, take a look at this trick!

Biologists are fascinated by the axolotl because it’s an amphibian that never grows up – giving it an amazing ability to regenerate. The species can re-grow entire limbs, heal parts of spinal cord, and even portions of the brain. Axolotls can recover from massive injuries – and can heal over and over again, with no sign of scarring. And it gets better – they’re also over 1,000 times more resistant to cancer than mammals. Scientists are exploring how these unique “superhealing” abilities work, with the hope of (eventually) being able to heal human tissues, improving success for burn victims, transplant recipients, and even cancer patients.

The question is what the chances are for wild axolotls in the meantime: Zambrano and his team are trying to create wild refuges so that these populations, too, can bounce back. The restoration of the Parco Ecologico Xochimilco over the last 20 years is one of the projects to reclaim crucial habitat for this one-of-a-kind animal.

Walking Catfish (Clarias batrachus)


Source: © CAFS

Sometimes being a relentless survivor can be trouble. That’s often the case with invasive species, which use unique qualities evolved in their native environment to take over other areas that don’t have environmental means to control them. This is true of the incredible walking catfish, our new feature in the Cabinet of Freshwater Curiosities.

Wait. A fish that walks?

Curiouser and curiouser, isn’t it? This bizarre, tenacious animal, originally from southeastern Asia, lives in the stagnant waters and mud of slow-moving rivers, swamps, and ponds, as well as ditches, flooded fields, and rice paddies. However, when it gets the urge to move – for example, if it gets stuck in a temporary pool left after a river flood – it can “walk” across dry land to find a new home. This walking is really more of a wriggle: the fish uses its spiny pectoral fins and twists its body back and forth to waddle awkwardly along the ground. It actually breathes air on these journeys, since it has a special organ that supports its gills, working almost like a lung. Walking catfish can survive out of the water as long as they stay moist – instead of scales, their skin is protected by a layer of mucus. Breathing air also allows them to thrive in “hypoxic” or oxygen-poor water, where other species can’t survive.

So it not only walks, it breathes air and lives in an otherwise deadly environment? Cool!

Well, not totally. The same unique adaptations that make the walking catfish so fascinating also make it a particularly troublesome pest – the Encyclopedia of Life has it on a list of 100 of the world’s worst invasive species. It is found across Southeastern Asia including eastern India, Bangladesh, Myanmar, Thailand, Malaysia, Indonesia, Singapore, Borneo, Laos and the Philippines, although it’s difficult to say how much of this is its original range. In Florida, where it was introduced for aquaculture in the 1960s, it spread into 20 counties within a decade, turning the state’s extensive canal system into an invasion highway. By the 1970s, researchers reported as much as 3,000 pounds per acre of invasive catfish in small Florida ponds, and they have also been found in other states as far apart as California and Connecticut, probably released deliberately or accidentally from aquariums.


Source: Image by: Pam Fuller, USGS

The slimy fish is voracious, eating a smorgasbord of smaller fishes, eggs and larvae, crustaceans and insects, as well as aquatic plants and debris. It can “walk” to isolated pools that are safe from many other species, and is a nightmare for aquaculture, walking from one fish farm to the next and gorging on fish stock, causing millions of dollars of damage. Many countries including the US require a permit to possess the fish, although there are still reports of pet stores selling them. However, controlling them is nearly impossible, since they can easily move to new habitats and can also wriggle into the mud and survive for months without food.


Source: © WoRMS for SMEBD

Ok, so not so cool. Does anyone like the walking catfish?

Although it’s got an undeniably bad reputation as an invasive species, in its native range in Asia it is highly valued by both commercial and subsistence fisherman. The fact that it can survive for so long out of water makes it more attractive because fishermen can easily trade live fish. But it’s a bit of a shocker in Florida when you see a school of thirty fish come up out of the sewer to take a stroll down the street!

Liberian Tree-Hole Crab (Globonautes macropus)

A freshwater crab that lives in a tree!?

Liberian tree-hole crab (Globonautes macropus)

Liberian tree-hole crab (Globonautes macropus)

What is it?

When we think of freshwater biodiversity we naturally think of places such as rivers, streams, ponds and lakes. But not all freshwater animals live in these habitats. The Liberian tree-hole crab is an amazing species of freshwater crab that lives in the closed canopy rain forests of West Africa. Yep, it’s a freshwater crab that lives in a forest. Living far from permanent freshwater sources such as rivers or lakes, these crabs live in water-filled holes in trees to survive. At night they emerge from their homes in the trees and make their way down to the forest floor to forage for food, mostly small insects. Once they’re finished with their evening meal, they climb back up the tree where they spend their days.

Map of West Africa

Map of West Africa

Range and Habitat

This unique species was first documented in 1898 in Liberia (hence the name), but was not documented until 90 years later in 1988. It is one of only five species that belong to a rare group of freshwater crabs that are endemic to West Africa. Since 1988 sightings have increased but been restricted to small parts of the upper Guinea forest in western Liberia and Guinea and it is also thought their range extends to parts of Sierra Leone’s forest which lie between these two populations. The crab populations are solely restricted to rainforest in areas with rainwater filled natural holes found in suitably sized trees at a height of between 1 to 2 meters above the ground and they are known to exist in just five different locations across these regions. For an interactive map of the tree-hole crab’s range click here.

The Upper Guinea Forest extends from Guinea into Sierra Leone and eastward through Liberia, Côte d’Ivoire and Ghana into western Togo.

The Upper Guinea Forest extends from Guinea into Sierra Leone and eastward through Liberia, Côte d’Ivoire and Ghana into western Togo.


As such these tree-climbing crabs are extremely rare and can be hard to spot. The number of tree-hole crabs that still exist is uncertain due to a lack of information, however, it was estimated that before the civil war broke out in Liberia in 1989 there were between 5-10 per km² of closed-canopy rain forest. It is expected that this number has decreased since this time and the species is listed as endangered on the IUCN Red List. Current estimates put the number at fewer than 2500 mature individuals.

It is thought that the population numbers have been declining across its range due largely to habitat loss and deforestation related to years of civil war and political instability in the region. Due to the specific habitat of these cool crustaceans they are very vulnerable to habitat loss. Being a freshwater crab that relies on rainwater captured in tree holes, even the felling of a small number of appropriately hollowed trees in a particular area may threaten local populations. Other threats that these curious critters face include an increase in agriculture, mining and firewood collection, which again contribute to habitat loss. Given these threats, the tree-hole crab’s specialised habitat and small population size, it is of serious concern that this species is not found within a protected area, nor are there any conservation measures in place to protect this unique animal’s existence. Hopefully more research into this incredible creature will raise awareness of its plight and spur on effects to protect it.

Further information:

IUCN Red List of Threatened Species

Fantastic Fire Salamanders – Salamandra salamandra

Slimy and sublime, but do they really “live in fire”?

Fire salamander head shot with view of parotoid glands. Photo by Didier Descouens.

Salamandra salamandra

The name European (or fire) salamander covers a number of salamander subspecies generally found in the mountain forests of western, central and southern Europe, although some populations can be found in North Africa and the Middle East.  There are 13 subspecies; all varying in colour, behaviour and adaptations, but generally fire salamanders are sturdy looking amphibians with a variety of yellow to orange markings on their back. Adults can grow up to a foot long and have been known to live for as long as 50 years in captivity, but ages of 30+ have been recorded in the wild!

Most of these secretive salamanders inhabit moist woodlands where they like to hide under rocks and logs and dig into the leaf litter. Although the adults are terrible swimmers they are never far from the freshwater streams and small pools in which they begin their lives.  Fire salamanders are most active at night, but can be found out and about on damp, overcast days; any time that you are likely to find slugs, worms and other goodies creeping about for hungry amphibians to snack on!  Salamanders catch their prey by sneaking up on an unsuspecting bug and firing their super-sticky tongue out… Gulp! Look at the video below for some fire salamander hunting behaviour.

Water babies

Like all amphibians, fire salamanders spend part of their lives in water. As adults they are poor swimmers, but their larvae need to spend the first 3 months in water (breathing through gills) before metamorphosing into tiny brightly coloured adults and leaving their aquatic birthplace.

Mating between male and female fire salamanders usually takes place in the cooler months, before the winter hibernation.  After blocking the female’s path and rubbing her with his chin the male plants a sticky spermatophore onto the ground and then sala-manhandles (sorry) the female until her cloaca is positioned over it. After fertilization the eggs develop internally.  When the eggs are ready to hatch into larvae, often in the following spring, the female will lay them directly into water where they will immediately hatch.  This process, called ovoviviparity, is common in many aquatic vertebrates, but a few sub-species of Fire salamander also give birth to live young – viviparity!

Creatures of habit, most fire salamanders return to the same cave, crevice or log every day and generally stick to foraging from this location. Some individuals have even been recorded using the same hibernation place for over 20 years! The actual distances that an individual salamander can range for food is quite large, on average around 500m².

Toxic to the touch

An animal which is fairly sluggish and confined to the ground, the fire salamander is vulnerable to predation from other vertebrates, but has a cunning adaptation to discourage being eaten. Upon closer inspection, the upper dermis of all subspecies of fire salamander is covered in small glands which secrete both protective mucus and a powerful neurotoxin.

The compound samadarine isolated from fire salamander skin secretion. Image from Wikipedia.

Two major alkaloids, samandarine and samandarone have been isolated from these skin secretions. These compounds are skin irritants and also disrupt the vertebrate nervous system causing hyperventilation and convulsions. Some species are capable of actively squirting this poisonous cocktail from the parotoid glands just behind the head.  The yellow and black warning colouration helps predators to identify the potential prey as toxic.

Fire salamanders and people

Despite Salamandra coming from the name for a mythical fire lizard, and their “fiery” colouring, the fire salamander would not survive any type of extreme heat.  It’s thought that the common name for these amphibians originates due to their sudden appearance from logs that have been collected for firewood, which is probably the only time that people normally encountered them.

With 13 subspecies distributed over such a large area, people and salamanders are bound to come in to contact with each other. Although currently designated as a species of “least concern” by the IUCN, fire salamanders are at threat from habitat loss, pollution and climate change.  For a species so dependent on cool, wet conditions long-term changes in weather patterns could influence the range of current salamander populations.  Perhaps their major disadvantage lies in the fact that comparatively little is known about many of the subspecies.  Some, such as Salamandra salamandra terrestris, are now commonly kept as pets so much of what we know about their behaviour has been recorded from captive populations.  But those subspecies found in more remote areas are poorly understood and therefore difficult to protect. There is also a tendency to focus only on the aquatic stage in conservation research, but the adult population is just as vulnerable to habitat change.

Fancy seeing a fire salamander in the flesh?  Head to your nearest zoo or wildlife park, they make great exhibits so most places will have them! Check out the video below for some more fire salamander action in their natural habitat.

Arapaima – Freshwater Giants of South America

Ancient armored freshwater fish crushes prey with a toothed, bony tongue

Guest curator: Daniel Gurdak (SUNY-ESF)

Arapaima sp. from Guyana. Image: D.J. Stewart

Arapaima are the largest scaled freshwater fishes in the world. Known by several names, including pirarucu (Portuguese) and paiche (Spanish), they can grow to an amazing 3 m in length and weigh up to 200 kg! These tropical giants are naturally found in the rivers and floodplain lakes of Brazil, Columbia, Ecuador, Guyana, and Peru, but have been introduced to other parts of South America and around the world.

A little bit about a big fish

The groups of species found in the genus Arapaima are part of the family Osteoglossidae, an ancient group of fishes known as the “bony-tongues”.  These freshwater monsters have not changed much in the last 13 million years!  Large, powerful and covered with an armor of hard, overlapping scales, arapaima are well equipped to survive attacks from piranhas, crocodilians and even people. Arapaima are fearsome predators -prey are sucked in and crushed between their bony, toothed tongue and a bony plate on the roof of their mouth! (See the feeding video below).

Unlike most fish, arapaima need to come to the surface every 15-20 minutes to breath air. They have a weird swim bladder lined with blood vessels which works as a primitive lung. Indeed, if an adult arapaima can’t surface to breathe it will drown! Baby arapaima hatch with working gills but can only breathe under water for just over a week. In the tropics the ability to breathe air is an advantage. This is because the combination of slow moving water, high temperatures and decomposing plant material often deprive the water of dissolved oxygen.

About their ecology and behavior

Arapaima live mostly in lakes, quiet backwaters of large rivers and adjacent floodplains. The tropical floodplain is a unique ecosystem with high and low water seasons, it is neither “terrestrial” nor “aquatic”, but both and somewhere in between. Floodplain plants and animals in the Amazon are highly adapted to annual changes in water height.  For example, when water is low, fish can become concentrated in river channels and lakes. However, as waters rise (by more than 10 m in some areas), fish move into the floodplain and feast on newly available plants, fruits, and insects.

Many fish, including the arapaima, reproduce during the beginning of the high water season.  Arapaima breed along the edges of lakes and channels in flooded forests. These are no ordinary fish – they build nests by digging a hole using their mouths, sometimes brushing away nearby leaves and branches! What’s more, arapaima parents work together to protect their eggs and young throughout the flood season.

The perils of being a large, tasty fish

For people of the Amazon Arapaima are great eating. The meat has few bones, firm texture, large fillets and tastes delicious. Sometimes called the “cod-fish” of the Amazon, it can be cooked fresh or used later by freezing or salting and drying.

Traditionally, arapaima were captured by fishermen with a harpoon or a bow and arrow.  Skilled fishermen wait patiently, and strike quickly when the fish rises up to breathe. Commercial fishing for arapaima began in the early 1800’s, and since then, over-fishing, in combination with increasing habitat degradation, has caused sharp declines in arapaima populations across much of their range. The video below shows fishermen catching arapaima.

Fishermen catching arapaima in Brazil. Images: Rafael Sá Leitão Barboza.

Arapaima today

Today, arapaima are faced with continuing habitat loss and insufficient legislation for their protection. In the depths of the rainforest any regulations are tricky to enforce. As a result, arapaima are recognized on two international endangered species lists as Arapaima gigas: IUCN Red List as “data deficient” and CITES “Appendix II”. To ensure the diversity and uniqueness of this genus is preserved, much about arapaima biology and its ecological relations in the wild still needs to be discovered.

Arapaima research in action. Image: D J Stewart

Where to see arapaima

Aside from tropical lakes and rivers (and some restaurants or fish markets), arapaima can be found in public aquaria and even in some pet shops around the world.  Keep in mind they will outgrow the average aquarium and probably the average aquarium keeper within a couple of years. With enough space and food, they can grow to 1 m in just a year!

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Diatoms: a freshwater curiosity

Imagine an organism that takes on a bewildering array of beautiful and complex forms and is common to almost all aquatic ecosystems, yet is invisible to the naked eye.  Organisms that have existed since the Jurassic period yet are being intensively researched by scientists looking for new breakthroughs in computer chip technology.   Look beneath the surface and discover the incredible diatom…

Asterionella formosa (Image: wikipedia)

Diatoms are a widespread group of algae that can be found almost anywhere there is water across the world.  With known records extending back over 180 million years ago, there are now thought to be over 100,000 species of diatoms globally, exhibiting an incredible variety of unusual and beautiful forms.

Diatom image from "Water Lives..." showing Gomphonema acuminatum var. coronatum animated by Adam Proctor (

For such a tiny organism, diatoms are incredibly important .  In freshwaters, diatoms are at the bottom of the food chain, and they are exceptionally sensitive indicators of water quality.  Tiny diatoms also provide a window into the past: as millions of individuals die and fall to the bottom of the lake they leave their fossil remains in the mud which carry clues to environmental history.  Living diatoms have very particular preferences for environmental conditions such as water pH, nutrient levels and water salinity.  This means that by examining the diatoms preserved in the layers of mud, scientists can ‘reconstruct’ past environmental conditions, information that is very useful for modern day environmental managers.  You can read more about this historical diatom detective work here.

Fragiliaria crotonensis (image:

New research in the semi-conductor industry is seeking to learn from the dense, complex shapes formed in the diatom silica shell as a means of designing faster computer chips.  Similarly, research is also being carried out on the lightweight but incredibly strong diatom cell structures by the aerospace and car industries, hoping to gain insights for designing new products.  You can read more about both these exciting research projects here.

Diatom image showing Fragiliaria crotonensis and Asterionella formosa from "Water Lives..." animated by Adam Proctor (

The range of complex diatom forms has fascinated scientists and amateur naturalists since the invention of the microscope, and provided abundant inspiration for our “Water Lives…” animation.  It was popular in Victorian England to mount kaleidoscopic arrays of diatoms on slides, adding another layer of glass to the organism’s fascinating display. Diatoms have also inspired artworks such as Ernst Haeckel’s 1904 Artforms of Nature, Liz Douglas’ “Mire” series of paintings, Klaus Kemp’s slide mounts and David Mann’s series of etchings and mezzotints.  A recent art-science collaboration between Dr Paul Hargreaves and Fay Darling brought the diatoms to life in a dazzling array of shapes and colours through the “colourising” of a set of scanning electron micrographs of the organisms.

Example of the stunning art-science collaboration work on diatoms by Fay Douglas and Dr Paul Hargreaves. Image: Fay Douglas and Dr Paul Hargreaves (

Many diatoms are pelagic, which means they spend their lives suspended in open water, living a ‘boom and bust’ life-cycle where population numbers wildly fluctuate depending on the amount of light and nutrients available from season to season. All diatoms have the same basic form, a single cell (either “centric” with a radial symmetry or “pennate” diatoms with a long axis symmetry) within a silica shell, called a frustule, generally between 0.005 and 0.2 millimetres in size (but can be up to a “gigantic” 1mm).  Diatom frustules fit together in two slightly overlapping valves like a hat box or Camembert case.

Cocconeis molesta var. crucifera. (Image: UCL,

Silica is used (amongst many other things) to make glass.  It could be said that diatoms live their entire life in glass houses – natural display cabinets for their amazing forms.  Diatoms divide to create two smaller daughter cells, each taking one half of the parent cell.  This means that as diatom populations grow, the average size of each individual decreases (up to a point where sexual reproduction takes place to produce a new full size  cell before the whole process repeats itself– imagine if that were true in humans!

Many thanks to Dr Rick Battarbee (BioFresh, University College London) and Dr Alistair Seddon (Long-term Ecology Laboratory in Department of Zoology, Oxford) for their input, advice and corrections on this article.

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