Sea Lamprey – Petromyzon marinus

Sea lamprey. Petromyzon marinus. Photo from US EPA.

Parasitic, jawless ‘vampire’ fish with toothy suction mouth

The sea lamprey (Petromyzon marinus) is one of the most wonderfully weird freshwater creatures we’ve featured in the Cabinet in some time.  Translated from a mixture of Greek and Latin, lamprey means ‘stone licker‘, most likely due to the fish’s tendency to hug the bottom of the rivers of Atlantic Europe and America that it inhabits with its curious sucker-like mouth (see the amazing close up photo above).  Unlike many other lampreys, for the sea lamprey, this fearsomely toothy mouth serves a deadly purpose: to suck the blood of unwitting fish.

Sea lampreys attached to an American Lake Trout. Image: Wikipedia

Sea lampreys attach their wraith-like bodies to the skin of passing fish (such as the lake trout, above), gripping with rows of tiny sharp teeth embedded in their suction-cup mouth and probing with a keen tongue to drain blood from the host’s body.  The lamprey’s fantastically odd characteristics: its eel-like, jawless body, the suction-cup mouth and its anadromous behaviour (i.e. lives in both the sea and freshwater), have led some scientists to contest that it should even be described as a ‘fish’ at all!

Sea lampreys in an aquarium. Image: Wikipedia

Despite these fearsome, wonderfully odd adaptations, within a healthy ecosystem (for example in the River Usk in the U.K.), the sea lamprey is important to the complex web of life, both as a predator and as prey (e.g. to birds such as herons, and to people – indeed King Henry I of England (1068–1135) was said to be so fond of the taste of lamprey that he died after eating ‘a surfeit’ of them!).  However, accidental introductions of the sea lamprey to the Great Lakes of America through shipping canals and container ships in the 1800s have caused an ecosystem crisis as the lamprey feasts on native lake trout, as described in the video below.

Millions of dollars have been spent in trying to eliminate the sea lamprey from the Great Lakes.  In 2009, under the headline “Sex smell lures ‘vampire’ to doom” (!), the BBC reported on conservation managers in the Great Lakes trialling the use of a laboratory version of a male sea lamprey pheromone, released into waterways to trick ovulating females into swimming upstream into traps.  However, the picture is not so rosy for the sea lamprey on the other side of the Atlantic Ocean.  Over the last century, sea lamprey numbers have declined dramatically in northern Europe, with no current breeding sites known of in the Baltic region.   As a result, conservation efforts are aimed at increasing sea lamprey populations in the region.

Isn’t it fascinating how perceptions and management of this much-maligned, incredible fish can vary so widely on different sides of the Atlantic? A true freshwater curiosity!

More information on the sea lamprey:

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The Iberian Peninsula: a European hotspot for freshwater diversity and curiosity

Achondrostoma: four tiny, beautiful fish species endemic to Iberia. Image: Ana Maria Geraldes

This month’s guest curator is Dr Ana Maria Geraldes from the Instituto Politécnico de Bragança in Portugal, who supplied the information about an incredible range of freshwater species found in the Iberian Peninsula (Spain, Portugal, Andorra and Gibraltar).

The Iberian Peninsula. Image: Wikipedia

The Iberian Peninsula is a hotspot for freshwater fish biodiversity and curiosity in Europe. The existence of geographical barriers such as the Atlantic Ocean, Mediterranean Sea and Pyrenees Mountains prevents fish from moving to other regions, creating a variety of different, isolated habitats, each subject to a wide range in climate.  This peculiar combination of factors has combined to produce a high number of endemic species through evolution.

What are ‘endemic species’?

Endemism is the word used to describe species that are only found in a very small habitat and nowhere else.  For example, the Galapagos tortoise is endemic to the Galapagos islands, because it is only found there (except in zoos, which don’t necessarily count as “native” habitats!).  Species become endemic to a small area because of geographical isolation, causing them to evolve in different ways to similar species found in other habitats (see for example, the differences between the Galapagos tortoise, and other tortoises found elsewhere).

Endemic fish species on the Iberian Peninsula: a hotbed of diversity and curiosity

The Iberian peninsula is home to 36 endemic species of cyprinids: tiny, shimmering and beautiful fish. Some are restricted to very small areas, such as the Southwestern arched-mouth nase (only named in 2005!), Portuguese arched-mouth nase, Western ruivaco, Squalius aradensis and Squalius torgalensis….not all of these fish are well-known enough to have been named yet!). More

Red bellied piranha – Pygocentrus nattereri

Red-bellied piranha. Image: Wikipedia

Infamous predators reveal more bark to their bite

What do we talk about when we talk about piranhas?  Huge teeth? Voracious appetites?  Frenzied feeding shoals?  All fascinating, and all true.  However, a new study by Belgian scientists has shown that one species of piranha has a similarly curious (and previous undocumented) characteristic: the ability to create an amazing, complex range of sounds.

Sandie Millot and colleagues at the University of Liege in Belgium used underwater microphones to record a shoal of piranhas during a range of different behaviours such as aggression, intimidation, food competition and chasing (all characteristics we’ve come to expect from Hollywood depictions of the fish…!).  Fascinatingly, the researchers found that the piranhas produced different, distinct sounds depending on their behaviour (play the audio below!).

The clip features three sounds.  The first is a “bark” produced in what the researchers called a “frontal display”, meaning where two fish swam quickly towards each other and stayed still, aggressively intimidating and staring at each other.  The second is a “drum beat” produced by the largest fish in the group when circling the shoal, mostly when there was competition for food.  The third “croak” was generally associated with a piranha chasing and biting another fish.

How the sounds are produced

The sounds are produced by the piranhas using their swimbladder – an organ which helps keep the fish buoyant and stable in the water.  The piranhas vary the sounds produced by quickly contracting muscles leading the swimbladder.  The rate at which the muscles contract varies the sound produced.

A fearsome reputation. A close up of the piranha's impressive teeth. Image: ARKive

Why is this important?

The piranhas in the study were silent for most of the time, only producing these weird and wonderful sounds during (very aggressive…!) social situations such as group feeding.  What this research shows, that hadn’t been seen (or heard) before, was that sound is a key part of how shoals of piranhas interact with each other.  The fact that all the sounds produced were associated with aggression only serves to reinforce the reputation of this fearsome little freshwater predator!  In fact, one of the researchers suffered a serious bite to their finger from the piranha when carrying out the recording…

Where does the red-bellied piranha live in the wild?

In the wild, the red-bellied piranha is native to the freshwater rivers of South America, congregating in large shoals.  Whilst the fish has a reputation for its aggressive feeding, it rarely feeds in groups, instead individually preying on fish and molluscs.  However, under conditions of extreme stress, the piranha shoals will exhibit a spectacular ‘feeding frenzy’ if presented with suitable food, potentially stripping a large item of prey to the bone in minutes.

More information:

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The Venezuelan Cave Cricket – Hydrolutos breweri

Head of a male Hydrolutos breweri. Image: C Brewer-Carias

This month’s curiosity is Hydrolutos breweri, a newly discovered flightless Venezuelan cricket which lives its entire life in perpetual darkness in the freshwater pools and streams flowing through caves atop high mountain plateaus.  As you can see in the video below, Hydrolutos is unlike any entry into the Cabinet so far!

Hydrolutos breweri is a member of a fascinating family of giant crickets from the Southern Hemisphere, the Anostostomatidae, which includes the Australian king cricket – which has been seen to overpower and eat large funnel-web spiders!

The new species was discovered in a gigantic quartzite cave – Cueva Charles Brewer (named after the Venezuelan explorer who “discovered” it, and famous for (amongst other things): “the discovery of the world’s largest quartzite cave and 27 plants, reptiles, insects and a scorpion named in his honour; a raft of diseases including malaria and leishmaniasis in his system; and a record for starting fire with sticks (2.7 seconds)”) – on a mountain plateau in eastern, Venezuela.

Known locally as “tepuis”, such table mountains rise sharply and dramatically up sheer cliffs from the lowlands, isolating the plants and animals they support on plateaus high above lowland ecosystems.

A Venezualan tepui rises sharply from the lowland landscape. Image: wikipedia

This detachment from the wider ecosystem allows species on the high tepuis to evolve in isolation over time, producing an incredibly rich biodiversity, consisting of many plants and animals with curious, unusual characteristics contained in a small area, a phenomenon known as endemism.  This isolated evolution atop high South American mountains inspired Arthur Conan Doyle to write The Lost World in 1912, a novel suggesting that dinosaurs and other prehistoric creatures still survived on such plateaus!

The incredible Cueva Charles Brewer. Image:

In 2010, an expedition was led by Charles Brewer-Carias and Branislav Smida to explore the gigantic quartzite Churi-tepui cave system in the Chimanta mountain range in eastern Venezuela.  The expedition discovered an incredible new insect, named Hydrolutos breweri after the explorer in a 2010 paper published by Tomas Derka and Peter Fedor.

Male Hydrolutos breweri. Image: Mr. Michal Poljak

The newly discovered cricket is found in the freshwater streams and pools that wind through the plateau cave system, where its strong legs and claws (see the picture above) allow it to grip, clamber and swim through a treacherous, slippery environment.  Incredibly, the cricket lives its entire life in perpetual darkness in the cave system.  However, the fact that Hydrolutos breweri doesn’t display any of the usual features of cave-dwelling insects (or “troglobionts”) such as tiny eyes or a whitening in body colour, means that this new discovery is likely to also be found in other streams and pools outside of the cave system.

Hydrolutos breweri in its natural environment. Image Tomas Lanczos

Another fascinating curiosity for the Cabinet of Freshwater Curiosities – who knows what the continued exploration of this amazing cave system will yield?  New freshwater plants and animals are being discovered every year, even in areas thought to be well explored and known – if you haven’t seen WWF’s report on their most recent expeditions in Papau New Guinea (where they found, amongst other things a previously undiscovered 2.5 metre long river shark and a “vampire frog”!), it’s well worth reading.

More information:

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Lesser water boatman – Micronecta scholtzi

Lesser waterboatman. Image: Jérôme Sueur

Tiny freshwater bugs create a cacophony in inventive ways…!

This month’s entry into the Cabinet of Freshwater Curiosities is the lesser waterboatman – Micronecta scholtzi – a common freshwater bug that produces a peculiar courtship song by rubbing its penis along its abdomen, a sound which reaches an incredible 99.2 db!  That’s a sound level equivalent to sitting in the front row of an orchestral concert, or standing close to a passing train!

As Dr James Windmill at the University of Strathclyde – a lead researcher on the June 2011 study “So Small, So Loud: Extremely High Sound Pressure Level from a Pygmy Aquatic Insect” published in the open-access journal PLoS – describes:

“Remarkably, even though 99% of sound is lost when transferring from water to air, the song is so loud that a person walking along the bank can actually hear these tiny creatures singing from the bottom of the river.”

The sound, used by tiny (2mm) males to attract mates, is produced by rubbing the penis and the abdomen together, in a process called stridulation. In the lesser waterboatmen the area used for stridulation is only about 50 micrometres across, roughly the width of a human hair.  This stridulation process is similar to that used by grasshoppers and crickets to produce their idiosynchratic chirps and chirrups.

Dr Windmill continues: “If you scale the sound level they produce against their body size, Micronecta scholtzi are without doubt the loudest animals on Earth.”

Animal noise/size comparison. Image:Jérôme Sueur

The loudest human shout ever recorded is 129db by British teaching assistant Jill Drake in 2000.  Sperm whales have been recorded emitting sounds reaching an incredible 236db, a cacophony required to communicate across vast, turbulent oceanic distances.  Decibels are a measure of the intensity or ‘loudness’ of a sound, measured on a logarithmic scale.  This means that for every increase of 10 decibels, there is a 10 fold increase in sound energy.


For comparison, a normal human conversation is generally measured at around 60db.  Incredibly, at 99.2db, the sound made by the lesser waterboatman is almost 10,000 times more powerful!  Whilst completely different in size, the incredible sounds emitted by both the lesser waterboatman and sperm whale, shows how aquatic animals have evolved to be able to communicate despite the muffling effects of the underwater environment.

This remarkable little bug is a fantastic wee addition to our Cabinet of Freshwater Curiosities, and like previous entries the bladderwort, the caddis larvae and the mayfly shows that incredible creatures live in the most everyday, developed freshwater environments: curiosity close to your home.

Let us know your thoughts on the waterboatman in the ratings and comments boxes below, and we’d welcome any budding “Curators of Curiosity” to get in touch using the box on the right with any amazing animals they’d like to see in the Cabinet in the future.

More links and information:

Strathclyde University Press Release on the story

Sueur et al 2011: The original journal article in PLoS One

Wired article on this incredible insect 

Wired article on the “bioacoustics” of animal sounds

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Pea frog of Borneo – Microhyla nepenthicola

© Prof. Indraneil Das/ Institute of Biodiversity and Environmental Conservation

The miniscule  Microhyla nepenthicola – also known as the mini or pea-frog – inhabits the heath forests of Borneo in SE Asia (see map below).  It was only formally described and named by Conservation International scientists in autumn 2010 (more information here), although it had been well documented for over 100 years.

Incredibly, whilst well-known to scientists, it had previously been thought that this tiny amphibian was a juvenile of other frog species in the genus Microhyla (which itself is populated only by tiny frogs!).  However, after tracking the diminutive frog’s unfamiliar, rasping call (only adult frogs emit calls) as it rippled through the rainforest in Kubah National Park around sunset, researchers found healthy populations living in and around the pitcher plants which thrive in the humid, shady conditions.

Listen to the pea-frog’s call

Pitcher plants: © Prof. Indraneil Das/ Institute of Biodiversity and Environmental Conservation

Many species of pitcher plants that grow in this habitat are carnivorous, trapping and digesting unwitting small insects lured in by bribes of nectar or visual lures (for more on carnivorous plants, see the intriguing bladderwort in the Cabinet).  Insects become trapped in liquid at the base of the pitcher, where they drown and dissolve.  However, improbably, this same liquid is where the pea-frog lays its spawn, and where its tadpoles develop until they emerge as adults.

© Prof. Indraneil Das/ Institute of Biodiversity and Environmental Conservation

The adult frog measures between 10.6 and 12.8mm (just look at how that compares to a coin in the picture, left!), and is the smallest known frog in the so-called “Old World” (which includes Asia, Africa and Europe).  Its “discovery” emerged from expeditions by Conservation International and IUCN’s Amphibian Specialist Group around the world in the hope of rediscovering 100 species of “lost” amphibians – animals considered potentially extinct but that may be holding on in a few remote places. You can find out more about this initiative here.

The Cabinet of Freshwater Curiosities is a place to collect and celebrate curious freshwater species, and the idea that there may be more, similar “curiosities” like the pea-frog awaiting discovery is extremely exciting.  If you have any curiosities of your own to contribute, we’d love to hear from you as we’re keen to feature more “guest curators”!

More information:

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Tisza mayfly – Palingenia longicauda

Long-tailed Mayflies (Palingenia longicauda) hatching in the Tisza River -- Solvin Zankl/Visuals Unlimited,Inc. ©

Guest curator: Following his extremely successful caddis fly entry into the Cabinet in March, BioFresh partner Dr Daniel Hering returns to showcase Palingenia longicaudia, or the Tisza mayfly – Europe’s largest mayfly.  You can find a special series of articles on the fascinating ecological, cultural and recreational importance of the mayfly on the BioFresh blog.

Mayflies are an abundant and diverse insect group occurring in running and to some degree in standing waters. In German, they are called “Eintagsfliegen” which means “one day flies”, as their winged, adult stage is very short – a few hours or a few days as a maximum. Most of their life-time, is spent as a larvae in the water, lasting for one year or more. Most species emerge in synchrony from the aquatic habitat in the summer, creating an incredible natural spectacle as blooms of the insect appear to dance above the river’s surface.

Almost all specimens of a mayfly species tend to leave the water within one or few days, creating huge clouds of swarming insects.  The advantages of this huge, synchronised hatch are obvious: as insects can only mate in their adult stage, by synchronising the hatch,  the chance of finding a partner is maximized – which is very important for species with such a short adult life stage. Predators like bats or birds are surprised by this sudden appearance of clouds of prey, and so can hunt only a small fraction of the population. The vast majority of mayflies die immediately after mating; in some cases the piles of dead mayflies block roads or bridges and need to be removed with a snow plow!

The swarming of mayflies is particularly impressive in case of large specimens, which used to be extremely abundant in large lowland rivers. Due to widespread pollution most of the large river species disappeared from European rivers in the 20th century but conservation efforts in the last two decades are helping some of them return.

Tisza mayfly (image: Lacitot,

However, Europe’s largest mayfly Palingenia longicauda, has managed to retain small but healthy populations around Hungary and northern Serbia.Palingenia specimens are about 4 cm long. They appear to be much larger, as they have up to 8 cm long appendages at their abdomen. The only large population of Palingenia longicauda, which has survived, is based in the Tisza river in Hungary. The species emerges around mid June, and event which is frequently referred to as “Tisza blooming” and is amongst the most fascinating natural phenomena in European rivers.

Tisza bloom (image: The Nature Animals)

This synchronised hatch is one of nature’s great sights, as the surprisingly large insects seem to dance above the river’s surface, smothering the riverbank and any other available surface (including cars, roads and people!) as they seek to find a mate in the short time available to them.  Hundreds of thousands of males fly towards the middle of the river to search for females which hatch at the water surface.  After mating the females may fly several kilometers upstream to compensate for downstream larval drift and laying their eggs along the way.  

And then as suddenly as it began, this fleeting, wonderful natural marvel is over.  Around the end of June the surface of the Tisza is covered with large dead mayflies, spent after their ephemeral existence is over. The larvae resulting from succesful mating grow in holes in the loam of the river bottom for three years, until they hatch and mayfly’s day-long dance is repeated once again.

More information

  • Wonderful gallery of high-resolution photos of the Tisza mayfly here
  • Arkive page here
  • Wild Serbia page on the Tisza mayfly

Arkive footage:

ARKive video - Male Tisza mayflies searching and competing for a female mateARKive video - Tisza mayflies swarming

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