Hey, Four-Eyed Fish!

Sure, those of us who wore glasses when we were younger may have been called “Hey, four eyes!”.  But I wonder if anyone ever took offense to the level of “Hey, you four-eyed fish!”.  ‘Cause that would be combining two insults, the discrimination against an ocular disability and the idea that you were kind of cold…or wishy-washy…well, anyway.  I sometimes get to share the fact that I once caught a Four-eyed Fish, and recently I found out that the species belonging to the Genus Anableps that I caught is rather rare, so I feel even more special!

(Imagine me affecting a British accent here, to make my story sound more adventurous).  “There I was, standing in the river with my doughty crew, when one of the young stalwarts excitedly shouted “Quatros ojos, quatros ojos!””.  Yes, just a few feet away from me cruised the rare and dangerous (dangerous if you’re an insect, that is) Pacific Foureyed Fish Anableps dowei!

In 1999 I accompanied members of my church on a mission trip to the area of Siguatepeque, Honduras, to assist in building cement block housing for victims of Hurricane Mitch (in 1998 Mitch was responsible for the death of at least 11,000 people in Central America) that caused a flood perhaps 40 feet deep in a valley near Siguatepeque.  After the rest of the mission left I stayed behind to travel to the Pan American School of Agriculture near Tegucigalpa, where the fisheries instructor there graciously allowed me to accompany them on trips to waters near the school.

view of Universidad Zamorano

Universidad Zamorano. Photo by EAP Zamorano [CC BY-SA 4.0], via Wikimedia Commons

The streams we sampled were the mainstem and tributaries of the Rio Choluteca, the major river on the Pacific slope of Honduras that winds through mountainous terrain until it empties into the Gulf of Fonseca, an estuary shared by El Salvador, Honduras and Nicaragua.  At a site on the Choluteca, near the village of Zamorano, the school’s students and I seined up the Pacific Foureyed Fish (Anableps dowei).  This was a species I’d read about prior to making the trip, so when I heard the student’s cry I became quite excited!

Drawing of a Foureyed Fish

Drawing by Unknown [Public domain], via Wikimedia Commons

The species is named for a Captain J. M. Dow, who skippered the steamer “Guatemala” of the Panama Railway Company.  Captain Dow collaborated with two associates to send over specimens from over 1500 samples in Central America to the U.S. National and the British Museums.

The reason for the Four-eyed Fish’s common name is the presence of two pupils in each eye, one in the upper and one in the lower half, separated by a band of tissue. This enables them to see above and below the water while they cruise at the surface of the water body and makes the Four-eyed Fish extremely difficult to catch with a seine: they are able to see you (or an eagle, or other bird of prey) coming from a long ways away. They are known to leap right over a seine and like fish in another family, topminnows, they dive down to the bottom to avoid capture.  An effective method of capture is described as using a group of fishermen to drive a school of quatros ojos toward a concealed individual waiting with a cast net that is thrown over the school, ensnaring a “bushel full” of the prey.

photo of Largescale Foureyes (from above water)

Largescale Foureyes, Trinidad. Photo by Charlesjsharp [CC BY-SA 4.0], via Wikimedia Commons

The Anableps‘ eye is flattened on the top and rounded on the bottom half, with a thickening of the lens from the bottom to the top to adjust for the refractive differences in the two mediums.  The upper pupil casts the terrestrial image through the lens on the lower retina, while the lower pupil’s image is reflected on the upper retina.  The Four-eyed Fish’s eye recently inspired at least one contact lense company to develop lenses that work extremely well both out of and in the water.


Scheme of the eyes of a four-eyed fish showing the basic functions

Diagram of the eye of a four-eyed fish, [public domain] via Wikimedia Commons

1. Underwater retina 2. Lens 3. Air pupil 4. Tissue band 5. Iris 6. Underwater pupil 7. Air retina 8. Optic nerve

Swimming at the surface with the head exposed is relatively unusual for fishes in general, but species of this genus show other oddities as well.  Not only do the quatros ojos leap out of and skip along the surface of the water, but when they see terrestrial insects on the banks they will actually leap onto the shallow, inundated bank side areas to capture their prey.  These fish have been observed lying in the sun, sometimes for several minutes, before pushing their way back into the water.  Once they’re out of the water their mobility is severely limited since unlike eels they cannot locomote with a wriggling motion, nor can they push off with their tails to leap forward on land. Unlike mudskippers and the “walking” catfish their pectoral fins are unsuited to pulling themselves along.  So, although they may push themselves along with their tail and pectoral fins to chase their prey, the extent to which they are able to do so is severely limited.

Another anomaly that characterizes anablepids is that their genital organs are oriented either to the left or right, thus they can reproduce only with mates having compatible organs.  They share this character with the group of species to which they are said to be most closely related, the “One-Sided Livebearers”, or Jennysina.  The functional significance of this anomaly is not known.  Anableps species are viviparious, meaning the young are birthed live rather than from an egg deposited in the water.  The eggs are carried to term inside follicles in the female’s ovary at which point they hatch and are extruded from the genital pore.  The male of the species has a gonopodium, a modified anal fin ray that develops as the males mature and facilitates placement of the sperm into the oviduct, fertilizing the female’s eggs.

At present three species of Four-eyed Fish are recognized: Anableps anableps, the Largescale Foureyes, is found in South America from the island of Trinidad and Tobago, and Venezuela to the Amazon Basin of Brazil.  Anableps dowei, the Pacific Foureyes, has the most limited distribution of the three species, occurring in Central America from southern Mexico to Nicaragua. Anableps microlepis, the Foureyes, is the most salt tolerant species of the three. They are found in open marine areas in full seawater (also from Trinidad to the Amazon Basin in Brazil) and follow tidal rhythms, moving up into sheltered lagoons and further upstream with the high tides, and back out into open waters as the tide wanes.

Anableps congregate in schools of up to 200 or so as juveniles, with their gregariousness decreasing with age until at adulthood they are as likely to be found as individuals as in small groups.  Some of their known fish associates include characins, pimelodid catfish, poeciliids, atherinids, eleotrids, flatfishes and cichlids.

If you are looking for an unusual fish for your aquarium the species that is most commonly available from suppliers (there are several that raise their own stock), the Four-Eyed Fish, is moderately hardy, but they are comparatively large in size, growing to around a foot in length.  Since they are surface swimmers they do best in a long, relatively shallow tank in fresh to moderately brackish water (depending on the species).  They are gregarious so it is best not to keep them singly or in pairs.  They will probably do well with Sailfin Mollies, bottom-dwelling Gobies, Mudskippers, and even Orange Chromide Cichlids, Archer Fish and Monodactylus.

The Family Anablepidae is placed within the Order Cyprinodontiformes (and, the Pacific Foureyed Fish attains the largest size of any species in that order).  That order contains a bounty of fascinating forms, with a wide variety of reproductive types, a plethora of adaptations to environments, and high importance in terms of biogeography.  My next post will portray some of those very diverse species.

About the Author: Marc Kibbey is Associate Curator of the Fish Division at the Museum of Biological Diversity.

*** Have you ever seen a four-eyed fish? Let us know, leave a comment ***

A newcomer to the OSUM Fish Division

We have several voucher specimens belonging to the order Salmoniformes, ray-finned fish like salmon, trout, chars, in our holdings, including the Lake Whitefish Coregonus clupeaformis. While common across most of their range, some are considered of special concern or vulnerable in the State of Ohio, for example, the Lake Trout Salvelinus namaycush. Another Coregonus species, the Cisco, is critically imperiled in Ohio, and Bloaters Coregonus hoyi (the hero of Monday’s post) were never found in Lake Erie due to the lake’s shallowness. Bloaters were extirpated from deeper Lake Ontario where the U.S. Fish & Wildlife Service is now reintroducing them. The specimens from the Tom Simon collection are the first Bloater vouchers (e.g. OSUM 117265) that we have for the OSUM fish collection.

By the way, a voucher specimen is a preserved specimen of an identified taxon permanently stored in our collection and retained as a reference. It has a unique identifier (e.g. OSUM 117265) and can be retrieved and used in scientific studies.

When moving the specimens, we needed many helping hands. Here Kai Raab, husband of OSUM Director Meg Daly, assisted with accession of some of the Tom Simon collection.

All Bloater specimens from the Tom Simon collection were trawled by the United States Geological Survey (USGS) during their surveys and have inflated gas bladders due to being brought from depths quickly.

The Bloater’s specific epithet, C. hoyi, is derived from the name of the man who originally discovered it while dredging in Lake Michigan, Dr. P. R Hoy. Dr. Hoy engaged ichthyologist Dr. James P. Milner to describe the species.

Coregonus is a diverse genus of fish with at least 68 described species. Some are easier to tell apart by morphology than others. Lake Whitefish, Coregonus clupeaformis, are separable from the Cisco and Bloater in the field by observing the mouth position: subterminal versus terminal, respectively. Note the terminal mouth, pointing forward, in the Cisco on the right.

Other species are quite similar in appearance and hard to separate in the field. For example, the Cisco and the Nipigon Cisco C. nipigon, as well as the Bloater and the Kiyi C. kiyi look very similar and occur sympatrically in some water bodies. For these and other species in the genus one must count the gill rakers to separate them. Gill rakers are the bony comb-like structure that serve to sieve food as the fish expels water through its gills while it is eating. The gill rakers are shown under the gill cover in the images below, to the left of the gill filaments that function to transfer oxygen from the water to capillaries. Once the food particles are caught on the rakers the fish can swallow them.

Cisco were found to have gill raker counts from 36 to 50, with a mean of 43 in Lake Saganaga and adjacent Minnesota border lakes. While gill raker counts for the Nipigon Cisco range between 45 to 70 with a higher mean than for the Cisco at 56.

Here are some additional species in the genus Coregonus; some are easy to tell apart by their location of occurrence.

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Etnier, David A., and Christopher E. Skelton (2003). Analysis of Three Cisco Forms (Coregonus, Samonidae) from Lake Saganaga and Adjacent Lakes near the Minnesota/Ontario Border. Copeia, Vol. 4, 739-749.


About the Author: Marc Kibbey is Associate Curator of the Fish Division at the Museum of Biological Diversity.


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The Bloater: A Complicated Story

You may recall from my last post that I mentioned a fish species from the recent Tom Simon Fish Collection acquisition, the “Bloater” Coregonus hoyi.  This is a species that in the recent past has been considered endangered, indeed it was known to be extirpated from some of the Great Lakes and thought to perhaps be on its way to extinction across the rest of its distribution.  Herein I’ll detail some of the reasons for which the bloater came to be in such peril.  But for now, allow me to follow a rabbitfish trail (ahem):

Perhaps you have wondered why this fish is named so cruelly?  Perhaps, one might think, the name was given in less politically correct days when short shrift was given to a fish’s feelings, but that is simply not the case.  No, the name actually describes the propensity of the species’ swim bladder to expand and make it look fat when it is trawled from the deep, colder waters that it prefers.  So you see it actually does have to do with the poor fish having a tendency to be gassy.

OSUM 117265 Coregonus hoyi "bloater"

Yes, that bladder does make you look fat! OSUM 117265 Coregonus hoyi 195mm SL 1 of 18 specimens from jar 1 of 3

The rapid ascent from the fairly extreme depths, down to almost 700 feet where the fish resides, and consequent distension of the bladder does cause more than just discomfort for the fish. The complexity of the connection to the gas bladder in the bloaters renders them unable to quickly discharge the air and liable to bursting upon fast ascent from depths.  In many species of fish the swim bladder is directly connected to the gut and the fish can use this connection to directly control the amount of gas in the bladder. This physostomous swim bladder occurs mainly in fish living in shallow waters and swallow air that is passed into the gut and forced into the swim bladder. Not so in the Bloater. Fish in the order Salmoniformes, such as the Bloater, share a character with other advanced fishes: the physoclistous swim bladder. This gas bladder has no direct connection to the alimentary canal but some areas of the membrane separating gut and bladder are very thin and well supplied with capillaries that allow rapid gas exchange. This gas gland secretes oxygen into the swim bladder through the rete mirabile, literally “a wonderful net” of capillaries.

Diagram of the arterial/venous transfer to the gas bladder via the rete mirabile

The Bloater is one of several  “whitefish” species that have become rare and imperiled, some to the point of extinction. Bloaters are invertivores – you guessed right, feed on invertebrates – at all stages of their lives and formerly fed in open water (Many other fish species are invertivores at immature stages and shift their diets to larger prey including vertebrates as adults).  It has been documented that bloaters (and some other fish species) have changed their feeding habits in response to competition from the invasive Alewife Alosa pseudoharengus to feed on benthic invertebrates.  Happily for the bloaters they seem to have benefited, in the long run, from the Alewife invasion.

But there are several other reasons for the drastic declines seen among the bloater populations during the mid-1900’s:  Whitefish provide table fare for many piscivorous people, the fish-eaters among you.  The major upswing of humans in the Midwest region caused concordant increases in demand for food sources, and people began to realize that the Great Lakes could provide fish aplenty to help meet that need.  The lakes and rivers of the Midwest states at one time “teemed with fish”, according to several historians that wrote during that era of expansion and discovery. It seemed that the bounty was inexhaustible, and fishermen quickly capitalized on the surging market, filling their trawl nets to capacity for several decades.

Until, at varying points depending on the species being taken, the catches began to dwindle.  Before long the fishermen began to realize that conservationists were correct in their assessment that the boom wasn’t going to last, and regulations were put in place to husband the resources. However, other influences began to make themselves known, some with alarming results. Compounding the effects of overfishing was the connection of Lake Ontario to Lake Erie via the Welland Canal ca. 1830 that enabled incursion of several invasive fish species:  First to make an impact was the Alewife, a relatively small fish species in the herring family Clupeidae. Alewives compete with coregonids and other fish species for planktonic prey, to the point where diets for some forms shifted from zooplankton to benthic foods, feeding at the lowest level of the water body. Those species that couldn’t adapt their diets disappeared, became smaller or declined in numbers.  The next invader to have a significant impact on bloaters was the Sea Lamprey Petromyzon marinus. Sea Lampreys are piscivorous parasites (or is that parasitic piscivores?) for approximately a year of their several years’ long life cycle.  The invasive lamprey arrived in the Great Lakes in the early 1900’s and by the mid 1900’s had decimated populations of several salmoniform species. It is thought that one reason fish species like Lake Trout, and Lake Whitefish and other coregonids, fared so poorly with the Sea Lampreys is that they tend to inhabit deeper, colder areas of the Great Lakes where the lampreys prefer to feed.  For example, bloaters are most commonly found at a depth of 90 – 680 feet in water temperatures between 34-55 degrees Fahrenheit. Thanks to the monumental efforts of our conservation agencies the Sea Lamprey populations are under reasonably good control to the point where Great Lakes fishes are much safer!



McDonald, M. E., Crowder, L. B., & Brandt, S. B. (1990). Changes in Mysis and Pontoporeia populations in southeastern Lake Michigan: a response to shifts in the fish community. Limnology and Oceanography, 35(1), 220-227.


About the Author: Marc Kibbey is Associate Curator of the Fish Division at the Museum of Biological Diversity.


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A time of giving – 10 million specimens

The Fish collection has undergone a dramatic growth spurt, more than doubling in size, through the gift of a collection of fishes held by Dr. Tom Simon. Our colleague served as an expert in fish and crayfish biodiversity for Indiana and taught courses on larval fish biology at OSU’s Stone Lab. The transfer of specimens was planned with Tom upon his retirement, but happened more quickly because of his sad, sudden passing.

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The relocation of the collection was spearheaded by Division of Fishes Curator Marc Kibbey, who served as logistics coordinator  and chief box mover for our three trips to the Bloomington facility where the material had been stored. Like so much of what we do, this move depended on the help of our students, volunteers, and colleagues, who showed up over several weekends to help us move thousands of boxes of specimens.

boxes organized for pick up

The students and friends helping in Bloomington organized boxes in advance of our arrival.

The Simon collection includes a synoptic collection of Indiana fish diversity plus extensive holdings of larval freshwater fish from across the US. It also contains historical collections that had been “orphaned” when institutions closed or experts retired. Unpacking and integrating the more than 10 million specimens we have acquired through this gift will occupy us for years to come. The tasks of accessioning, rehousing, and databasing the specimens are leavened by the opportunity to see so many fish, and to find some real gems within the collection.


About the Author: OSU Professor Meg Daly

Dr. Meg Daly is the Director of the OSU Museum of Biological Diversity, Professor in the department of Evolution, Ecology & Organismal Biology and manages the Lab of Marine Invertebrate Diversity.