Skull anatomy of S. rhombeus (photo by SH) and fossil teeth of M. paranensis (inset). © Cione et al.

New research published in the journal ‘Scientific Reports’ demonstrates the extraordinary bite force of modern day piranhas plus the extinct giant Miocene piranha, Megapiranha paranensis.

Pirhanas are included in the family Serrasalmidae which has three main evolutionary lineages, the carnivorous piranha-clade, the omnivorous Myleus-clade, and the herbivorous pacu-clade. Their teeth and dentition demonstrate a strong functional adaptation to diet, and these features have been used to classify them for decades.

For example, the carnivorous species typically have jaws lined with a single row of 6–7 serrated, multi-cusped, triangular, blade-like teeth, while those of herbivorous species tend to be flattened and molar-like.

The bite force of the black piranha, Serrasalmus rhombeus was used to predict that of Megapiranha. © Adam Carvalho

In 2009, Cione et al. described an extinct, giant serrasalmid species from a single fossilized premaxilla jaw bone fragment that had a set of three triangular teeth set in a zig-zag pattern.

Megapiranha paranensis inhabited the Paraná geological formation in Argentina around the time of the Miocene and its teeth have compressed pointed cusps with finely serrated cutting edges similar to those of a shark, but with a robust, broad base.

These morphological similarities with modern-day serrasalmids place M. paranensis as sister to the carnivorous piranha-clade but slightly intermediate with the herbivorous ‘pacu-clade’ of the Upper Miocene, and its teeth were seemingly equipped both to cut soft flesh and crush harder prey items.

The teeth of herbivorous serrasalmids are remarkably reminiscent of human molars. © JJ Photo

By recording the bite forces of the black piranha, Serrasalmus rhombeus, the largest modern-day serrasalmid, Justin Grubich and his team from the American University in Cairo were able to hypothesise the feeding ecology of M. paranensis, reconstruct its bite forces and investigate what its unique dentition might have been used for.

They concluded that for its relatively small size, Megapiranha paranensis‘ bite dwarfed that of other extinct mega-predators, including the infamous whale-eating shark Carcharodon megalodon and enormous Devonian placoderm, Dunkleosteus terrelli.

Their results show that S. rhombeus can produce an in-vivo bite force of 320 N, the strongest yet recorded for any bony or cartilaginous fish to date in relation to its size. In fact, this is a bite force in excess of 30 times its weight, and more than three times stronger than that of an equivalent-sized American alligator.

Bite Force Quotients of living and extinct apex predatory fishes. © Grubich et al.

This is achieved via over-sized adductor muscles in the mandible which in S. rhombeus‘ comprise more than 2% of its total body mass, another record among bony fishes, which function alongside a highly-modified jaw-closing lever.

S. rhombeus can grow to a length of 40-45 cm but Megapiranha measured at least 71.5 cm, and the scientists’ analysis predicted that its bite was equivalent to the anterior bite force of a great white shark weighing over 400 kg!

Its diet remains unclear, but the shape and morphology of its teeth makes them potentially-suited to deal with both soft and hard prey items, raising the question of whether they evolved in order to not only slice through flesh but also crush bone.

Hypothetically, it may therefore have preyed on turtles, armoured catfishes and, to a lesser extent, the limbs of larger terrestrial mammals.

For further information refer to the full, open access paper: Grubich, J. R., S. Huskey, S. Crofts, G. Orti and J. Porto. 2012. Mega-Bites: Extreme jaw forces of living and extinct piranhas (Serrasalmidae). Scientific Reports 2: article 1009

The study uses the zebra danio, Danio rerio, in its case example. © Mike Norén

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Boraras naevus has been in the aquarium hobby for several years now. © Peter Macguire

Three very different freshwater fishes are among ten animal and plant species highlighted in a new WWF report entitled ‘Extra Terrestrial’.

Among the 126 species newly identified by scientists in the Greater Mekong region in 2011 new were a bat named after its devilish appearance, a subterranean blind fish, a ruby-eyed pit viper, and a frog that sings like a bird.

“While the 2011 discoveries affirms the Mekong as a region of astonishing biodiversity, many new species are already struggling to survive in shrinking habitats,” said Nick Cox, Manager of the WWF’s Greater Mekong Species Programme.

Clarias gracilentus. © Ng Heok Hee

A new ‘walking’ catfish species Clarias gracilentus Ng, Hong & Tu 2011, discovered in freshwater streams on the Vietnamese island of Phu Quoc, can move across land using its pectoral fins to stay upright while it moves forward via snake-like movements.

A beautiful miniature fish, Boraras naevus Conway & Kottelat 2011, just 2cm in length, was found in southern Thailand and named after the large dark blotch on its golden body, naevus meaning ‘blemish’ in Latin.

It’s already known to aquarium hobbyists and is sometimes referred to as B. sp. ‘strawberry’ or B. sp. ‘red micros’.

Bangana musaei is a cave-dwelling cyprinid which lacks functioning eyes. © Helmut Steiner

A pearly, rose-tinted cyprinid  fish was discovered in the Xe Bangfai catchment, a Mekong River tributary in Central Laos that runs 7 km underground through limestone karst. The hypogean Bangana musaei Kottelat & Steiner 2011 is totally blind and was immediately assessed as vulnerable due to its restricted range.

The Mekong River supports around 850 fish species and the world’s most intensive inland fishery. Laos’ determination to construct the Xayaburi dam on the mainstream of the Mekong River is a significant threat to the Mekong’s extraordinary biodiversity and the productivity of this lifeline through Southeast Asia that supports the livelihoods of over 60 million people.

“The Mekong River supports levels of aquatic biodiversity second only to the Amazon River,” added Cox. “The Xayaburi dam would prove an impassable barrier for many fish species, signalling the demise for wildlife already known and as yet undiscovered.”

Proposed construction site for the Xayaburi Dam on the Mekong River in Northern Laos which the Laotian government are pressing ahead with despite opposition from neighbouring countries. © International Rivers

Extra Terrestrial spotlights 10 species newly identified by science, among the 82 plants, 13 fish, 21 reptiles, 5 amphibians and 5 mammals all discovered in 2011 within the Greater Mekong region of Southeast Asia that spans Cambodia, Laos, Myanmar, Thailand, Vietnam and the south-western Chinese province of Yunnan.

Since 1997, an incredible 1,710 new species from the Greater Mekong region have been described to science.

Click here to download the full report.

May we also extend congratulations to friends of SF Peter Macguire for his superb photos of Boraras naevus which are featured in the report, and Dr. Ng Heok Hee who co-described Clarias gracilentus.

The juvenile colour pattern has made this species a sought-after aquarium fish. © Stan Sung

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P. phoenicurus. © Schindler & Linke

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Live male paratype specimen. © Kowasupat et al.

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Phoxinus phoxinus, the Eurasian minnow. © Jack Perks

Conservation efforts for freshwater fishes tend to be concerned with large, often migratory, ‘flagship’ species such as salmon, trout, and sturgeon, but a new project funded by National Geographic and backed by the United Kingdom Environment Agency, among others, aims to catalogue populations of the smaller groups commonly referred to as ‘tiddlers’.

These fishes, which include the ninespine stickleback, Pungitus pungitius, spined loach, Cobitis taenia, and minnow, Phoxinus phoxinus, are mostly overlooked and not particularly well-known in the UK. However, in terms of biodiversity and ecosystem function they’re equally important as any other animal, plant or microorganism.

Cottus gobio is commonly known as the bullhead. © Jack Perks

Higher animals such as kingfishers and otters prey on them, for example, and their presence is often acknowledged as an indicator of the overall health of a habitat since they mostly inhabit pristine environments.

Brainchild of wildlife photographer and angler Jack Perks, the mini fish survey therefore hopes to establish patterns of distribution and abundance of these fishes throughout the country via an online form designed to be filled in by members of the public.

How can I help?

The project has Facebook and Twitter accounts, but what’s really needed in order for it to work is public involvement in the survey itself, so if you want to help the best thing to do is simply get involved!

If you live close to a river, stream, canal, pond or lake in the UK get out there, have a poke around with a net, lay a minnow or bottle trap overnight, or even follow Jack’s lead and don a wetsuit-snorkel combo to record out what inhabits your neighbourhood waters…

In the UK the spined loach, Cobitis taenia, is known from only 5 watersheds in eastern England. © Jack Perks

…record details of the species encountered then go and fill in the official survey form which is quick and easy to do. The links are as follows:

Survey: http://www.surveymonkey.com/s/99PXDHM

Facebook page: https://www.facebook.com/UkMiniFishStudy?ref=hl

Twitter: https://twitter.com/RiverFishUk

We think this is a super-positive initiative and hopefully it will not only provide important information to environmental authorities, but also raise overall awareness about freshwater fishes in the UK and beyond.

The full list of included species is as follows:

Blicca bjoerkna (silver bream)

© J.C. Schou

Pungitius pungitius (nine/ten-spined sticklback)

© Colin Dunlop

Phoxinus phoxinus (minnow)

© Matt Ford

Cottus gobio (bullhead)

© WoRMS

Cobitis taenia (spined loach)

© Jack Perks

Barbatula barbatula (stone loach)

© Jack Perks

Gymnocephalus cernua (ruffe)

© Tiit Hunt

Alburnus alburnus (bleak)

© David Perez

© Cucherousset et al.

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Matt Ford introduces a little-known group…

Male Aphanius iberus from the Delta del Llobregat, Barcelona. © Matt Ford

The traditional image of killifishes is that of ostentatious, highly-coloured African or American species from genera such as Aphyosemion, Nothobranchius or Simpsonichthys, but it might be surprising to learn that there also exist a number of rarely-discussed, very attractive species native to Eurasia of which several are found in southern Europe.

In particular the genus Aphanius Nardo, 1827 contains more than 20 species which are probable descendants of ancient fishes inhabiting the former Tethys Sea.

They’re found throughout the Mediterranean region and Arabian Peninsula as far as Pakistan and India with this irregular pattern of distribution a result of geologic activity during the Cenozoic Era, and most remaining populations are geographically isolated from one another.

Map of populations in Spain with A. iberus (dark blue) and A. baeticus (purple).

Species diversity is highest in the eastern Mediterranean, Middle and Near East regions with Turkey a particular hot-spot, whereas the western Mediterranean is less rich with only four native species of which two, Aphanius iberus (Valenciennes, 1846) and A. baeticus Doadrio, Carmona and Fernández-Delgado, 2002, are endemic to Spain.

These two were once widespread throughout lowland, littoral habitats in the country, but in the last century their range has diminished dramatically and they currently exist only in a handful of brackish and hyper-saline coastal lagoons, salt marshes, and first order streams along the country’s Mediterranean and Atlantic coastlines.

This huge decline has been caused exclusively by human interference via the detrimental impact of introduced species such as the mosquitofish, Gambusia holbrooki, and mummichog, Fundulus heteroclitus, plus extensive habitat degradation caused by dessication and pollution of wetlands and human overpopulation of many coastal areas.

Introduced Gambusia holbrooki are highly-invasive throughout Mediterranean Spain. © Matt Ford

Both species are considered to be under extreme risk of extinction, and as a result they’ve become largely inaccessible to aquarists, are protected under Spanish and European law and illegal to collect without a near-impossible to obtain license. Despite these measures their numbers continue to dwindle on an annual basis, however.

A. iberus (Valenciennes, 1846) is the most well-distributed of the two in nature and best-known in the aquarium hobby. It originally occurred along the majority of Spain’s Mediterranean coastline from Catalonia to Almería but a 2006 study for the IUCN concluded that its numbers had decreased by as much as 50% in the previous decade and it’s been protected under Spanish and international conservation law since 1994.

The 16 remaining subpopulations are highly-fragmented in geographical terms, with a resultant lack of genetic flow. The situation is hardly aided by the indifference of the national authorities towards fish conservation in general, and even management of existing protected zones is totally inadequate.

The ‘Arroyo Mascardó’ in Sevilla province is a typical habitat of A. baeticus which has been degraded by human activity without intervention by authorities. © Matt Ford

For example the mummichog was originally restricted to a relatively small area in southern Spain but has recently been recorded around 800 km further north in the Ebro river delta, a wetland and natural park of internationally-recognised conservation significance which also happens to be saturated with invasive fish species.

A. baeticus was previously considered to be a geographic form of A. iberus and is restricted to less than a dozen localities mostly within the lower Guadalquivir River basin and along Spain’s southern Atlantic coastline.

Adult male of A. baeticus from the Río de la Vega, Andalucía. © Matt Ford

Although it looks very similar it can be told apart from A. iberus by possession of  9-11 branched anal-fin rays (vs. 8-9 in A. iberus), a noticeably shorter snout, relatively thick (vs. thin) vertical bars in males and a flank patterning consisting of a few large (vs. numerous, small) dark markings in females.

The reproductive biology of Iberian Aphanius shows adaptations typical of species inhabiting unstable environments and is characterised by early sexual maturity, a high reproductive effort and short lifespan with most individuals surviving less than a year.

Females spawn continuously between the months of April and September and can deposit over 1000 eggs over the course of the season. These are laid singly or in small batches among aquatic vegetation or filamentous algae and hatch in around 8 days.

Adult female of A. baeticus from the Río de la Vega. © Matt Ford

Sexual dimorphism in both species is pronounced with males possessing a series of steely-blue vertical bars in the posterior portion of the body, these becoming more intense in nuptial individuals.

Females are less colourful, possessing only a series of irregular dark blotches on the flanks, and larger with a maximum size of around 50 mm SL compared with 35-40 mm in males.

Aquarium breeding is not difficult but at time of writing it remains illegal to remove either species from their natural waters and the fish shown here were released immediately after being photographed.

Flank patterning of male A. baeticus (left) vs. A. iberus. © Matt Ford

Case example

I first visited the Río de la Vega in Andalucía, southern Spain while sampling several rivers in the area in late August 2008. It’s a short, first-order river rising in the mountains of the El Estrecho Natural Park, its lower reaches running alongside the coastal town of Tarifa before emptying into the Atlantic.

This area is notable for its great diversity of bird and marine life as well as its position as the southernmost point in Europe. Northern Morocco can appear to be within touching distance on a clear day and the stretch of coastline close to the town is one of the few in the south of Spain yet to have been destroyed by tourist developments.

The Río de la Vega in summer. © Matt Ford

Although there were plenty of A. baeticus here the situation initially appeared dire as the fish were surviving in what amounted to little more than a series of large puddles in the dry river bed. Worse, they were concentrated underneath a motorway bridge and directly adjacent to a new commercial development.

The pool under the bridge in particular was filthy and contained a number of aluminium cans and other refuse. Sympatric species in the pools included an Atherina species, probably A. boyeri, the invasive and highly-destructive red swamp crayfish Procambarus clarkii, two species of shrimp and the spined loach Cobitis paludica, another endangered Spanish endemic that I was very pleased to find.

The loach Cobitis paludica is another Spanish endemic inhabiting the Río de la Vega. © Matt Ford

Subsequent visits in 2009, 2010, and 2011 made for enlightening experiences since the habitat is highly seasonal in nature, so while one can walk along the dry bed for several hundred metres during summer this is impossible in autumn, winter and spring due to the beautiful, flowing river which is several metres deep in places!

During these three seasons A. baeticus can be found in both slow-moving, clear water and faster-flowing, more turbid sections of the river, but always in marginal zones with submerged grasses, filamentous algae and riparian vegetation.

It’s restricted to a freshwater stretch a few hundred metres from the sea and it’s this limited range along with the proximity of the habitat to human developments that places this population in a precarious position.

The Río de la Vega in spring. © Matt Ford

Furthermore southern Spain is in the midst of an ongoing water shortage and it’s conceivable that a couple of dry summers could eradicate the temporary pools in which the fish spend the warmer months of the year, plus the habitat is not formally protected.

Despite the gloom there are reasons for positivity, and I’m proud to be involved with the Sociedad de Estudios Ictiológicos (Society of Ichthyological Studies), one of the few groups in the country concerned with preservation of these little-known killifishes. Look out for more about them and their work in upcoming blogs and articles.

References:

Doadrio, I., J. A. Carmona and C. Fernández-Delgado, 2002. Morphometric study of the Iberian Aphanius (Actinopterygii, Cyprinodontiformes), with description of a new species. Folia Zoologica 51: 67–79

Hrbek, T. and A. Meyer, 2003. Closing of the Tethys Sea and the phylogeny of Eurasian killifishes (Cyprinodontiformes: Cyprinodontidae). Journal of Evolutionary Biology 16(1): 17-36

Oliva-Paterna, F. J., I. Doadrio. and C. Fernández-Delgado, 2006. Threatened Fishes of the World: Aphanius baeticus (Doadrio, Carmona & Fernández Delgado, 2002) (Cyprinodontidae). Environmental  Biology of Fishes 75(4): 415-417

Oliva-Paterna, F., M. Torralva and C. Fernández-Delgado, 2006. Threatened Fishes of the World: Aphanius iberus (Cuvier & Valenciennes, 1846) (Cyprinodontidae). Environmental  Biology of Fishes 75(3): 307-309

Wildekamp, R.H., F. Küçük, M. Ünlüsayin, and W. V. Neer, 1999. Species and Subspecies of the Genus Aphanius Nardo 1897 (Pisces: Cyprinodontidae) in Turkey. Turkish Journal of Zoology 23: 23-44

Blanco, J.L., T. Hrbek and I. Doadrio, 2006. A new species of the genus Aphanius (Nardo, 1832) (Actinopterygii, Cyprinodontidae) from Algeria. Zootaxa 1158: 39-53

Fin-flaring, as seen here, is a behaviour typical of aggressive encounters between male fighting fish. © Chor Kiat Yeo

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