Four Eyed Fish

Sure, those of us who wore glasses when we were younger may have been called “Hey, four eyes!”.  But I bet none were ever taken to the level of “Hey, 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 would like to share some very interesting information about the species.

(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 four-eyed fish!  Alright, enough of that…

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 group 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.  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 Four-eyed Fish (Anableps dowi).  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!


The species was 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 Foureyes’ common name is actually due to the presence of two pupils in each eye, one in the upper and one in the lower half and separated by a band of tissue; enabling them to see above and below the water while they cruise at the surface of the water body.  That ability makes the foureyed fish extremely difficult to catch with a seine since 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 other “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 cuatros ojos toward a concealed individual waiting with a cast net that is thrown over the school, ensnaring a “bushel full” of the prey.



The 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.  This structure has inspired at least one contact lense company to develop lenses that work extremely well both out of and in the water.


The Four-eyed fish eye. 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 the genus exhibit 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 bankside areas to capture their prey.


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, and 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…  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.  The eggs are carried to term inside follicles in the female’s ovary but nourishment is provided by a yolk sac within the egg.

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.


The Family Anablepidae is placed within the Order Cyprinodontiformes (the Pacific Foureyed Fish is the largest 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.  Cyprinodontiformes is made up of families that for the most part exclusively are either oviparous (egg laying), ovoviviparous (live-birthed from eggs) or viviparous (live-birthed from embryonic development without eggs).  Species of the family Anablepidae are found in rivers and streams (some (such as the Pacific Four-eyed Fish) live and thrive in euryhaline and even marine areas) from Mexico to South America, and are ovoviviparous, or live bearers; similar to guppies and mosquitofish.   Owing to the ability of many species to tolerate a wide range of salinities the cyprinodontoids are able to move along the coast from one stream to a neighboring stream.  It is thought that this plasticity has enabled certain groups to disperse throughout southern Mexico to northern South America.

Anableps have an unusual and interesting lifestyle. They spend almost all of their time at the surface and rarely swim underwater. They will dive down when they spot a food item, though, using their large, paddle-like pectoral fins for a burst of speed. They will also leap onto mud and sand banks during periods of low-tide to snatch terrestrial insects. These fish have been observed lying in the sun, sometimes for several minutes, before pushing their way back into the water.

Four-Eyed Fish are moderately hardy, but they are comparatively large livebearers, growing to around a foot in length.  Since they are surface swimmers they do best in a long, relatively shallow tank in (depending on the species) fresh to moderately brackish water.  They are gregarious so don’t 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.

Once Upon a Time a Beautiful Fish Lived There

In the colder waters of North America lives what is perhaps the most beautiful freshwater fish, the Arctic Grayling.

What an elegant animal!  Sometimes called the “sailfish of the north”, this species is best known for the large dorsal fin that exhibits gorgeous colors!

The arctic grayling is circumpolar in distribution, with stable populations across northern North America from Alaska to Newfoundland Canada, and across northern Asia from westernmost to easternmost Russia.   So, while there is no danger of extinction across the worldwide range of the species, one population in Michigan was extirpated, and the only other known, native population in the contiguous United States, in Montana, was almost extirpated as well.

Once abundant enough to “walk across the river on the backs of the fish”, native populations of the Michigan grayling are extinct.  Their demise resulted from logging that removed the large trees along the banks of the rivers and streams that served to cool the waters along with the practice of sending the cut logs downriver that destroyed habitat and impacted the eggs and larvae in the rivers, and unrestricted fishing during the spawning season.

Arctic grayling were successfully stocked  a few years ago in privately owned Brookhaven Lake Brookhaven Lake ( near the south-central portion of the Upper Penninsula Michigan, and can be fly fished there with reservations.  But there are currently collaborative efforts underway to stock nearly identical subspecies of the arctic grayling in the Manistee River that flows into Lake Michigan.

We have two specimens from Michigan, one a skin mount from a grayling caught in 1880 from the Au Sable River in Michigan, the other caught in 1938 by longtime OSU-MBD curator Milton B. Trautman (huh…”Trautman”…figures eh?) from Ford Lake in Michigan, where the species was stocked.  The Au Sable River heads up near Grayling, Michigan (of course!) and flows into Lake Huron through (what could be more appropriately named than) Au Sable, Michigan.  A total of 15 arctic grayling vouchers are cataloged at the OSUM (Ohio State University Museum of Biological Diversity) from Alaska, Michigan, Montana, Ohio, and Ontario Canada.  One of those vouchers represents one specimen caught in 1968 from Lake Erie near Cleveland Ohio, but this specimen either was stocked by the ODNR or from a private lake, or strayed from Ontario (where it was stocked and is listed as an exotic species), or southern Michigan.

References: California Academy of Sciences Catalog of Fishes, Hubbs and Lagler Fishes of the Great Lakes, Scott and Crossman Fishes of Canada

Arctic Grayling (Thymallus arcticus) – Species Profile (

A Marvelously Successful Invader

Consider the round goby, a much maligned fish species due mainly to their success in colonizing many waterways including the Great Lakes.  One might wonder whether more fishermen have cursed the ugly, unappetizing fish when it greedily grabs their bait than have berated the other “useless” invader; common carp, in the few years the goby has been in the Great Lakes compared to common carp that were introduced intentionally across the country by the U.S. Fish Commission in the 1880’s.  In all actuality though, there is much to be admired about this quarter-pint-sized interloper!

The first round goby taken in Lake Erie was electroshocked by Dr. Roger Thoma, formerly of the Ohio EPA Surface Water Division, inside the breakwall at the Grand River harbor in 1993. Given the distance of the first sighting of the round goby from the St. Clair River where it first appeared in 1990, the goby may have been in Lake Erie a couple years before 1993.

If you were planning to invade an ecosystem, what skills would you have that would enable you to do so as efficiently as this happy little fish in the picture below?  One characteristic would be a sound reproductive strategy, and the round goby excels in this area with eggs that are larger than other species of similar size enabling better survival of the young, especially when coupled with the strong parental care exhibited by the round goby.  The male tends the nest, cleaning and guarding it from predators.  Round gobies are known to be highly aggressive, invading the most suitable territories for their nests and predations, as well as waiting rapaciously for much larger black basses to leave their nests even for a moment to grab a morsel to eat at which point the pugnacious goby rushes in to gobble up eggs and larvae.


So, is the only good round goby a dead round goby?  Not in the strictest sense, if you’re a Great Lakes water snake, or a cormorant (that also prey on and have benefitted from the “explosion” of the water snake population), or even a bass.  See, those are all just a few of the many animals that have benefitted from the abundance of round gobies.


The Olentangy River Shark


How in the world did this shark swim up into the Olentangy River?!  Do we need to worry about our dogs retrieving frisbees thrown from the banks of the river?

No, no worries.  This species is exclusively marine and would never enter freshwater streams although they may stray into estuaries from time to time, their bodies could not adapt to the change in salinity unlike the bull shark and several other fish species.

But on 08 August 1976 an Atlantic sharpnose shark was found on the bank of a tributary to the Olentangy River…dead.  How did it get there?  Perhaps someone caught it off the shores of New Jersey where they are one of the most common shark species Atlantic sharpnose shark – Wikipedia in the nearshore waters of the west central Atlantic Ocean.  Even if they could survive in freshwater they seldom attain more than 4 feet in length.

Oddly though, just a little less than 40 years later another Atlantic sharpnose shark was found floating, dead, in the Ohio River near Manchester Ohio and is also vouchered here in the OSUM Fish Collection (

For more information on these specimens OSUM 54284 and OSUM 115521 navigate to, click on the Fish Division Database bar and enter OSUM and the number into the search bar.  Alternatively you can search for this and other species in our database for vouchers held in our collection.

What’s New in the Fish Division

This will be the first of an installment of posts on fish species cataloged in the Fish Division.  I really enjoy my work, particularly when I get to identify species that i’m unfamiliar with.  And when you consider that there are more than 33,000 species in the world (with more being described almost every day) i’m not ashamed to say that I anticipate being able to encounter unfamiliar species for a long time to come!

Recently one of our associates, Miriam Gibbs, found several boxes of specimens that probably were brought in during the tenure of former curator Milton Trautman.  Most of the vouchers were from a series of collections that were made by ichthyologists working off the western coast of Mexico below Baja California, particularly around the “Islas Marias“, or Tres Marias islands.  The Tres Marias are actually a group of four islands that until February 2019 was a Mexican white collar penal colony.  Most of the Tres Marias specimens were collected by divers using rotenone (The chemical rotenone interferes with a fishes’ mitochondrial electron transport, killing the fish.).  It is said that rotenone has ” has only minor and transient environmental side effects”.  I’ll stick with seining, electroshocking and trawling.  Here are a few of the species I’ve been adding to our collection (many of which are actually new to the OSU Fish Division), click on the genus and species name to go to a series of images hosted by

scissortail damselfish Chromis atrilobata Family Pomacentridae (damselfishes)

Most damselfishes are marine, but a few are euryhaline and thrive in estuaries with some of those (such as the freshwater demoiselle) swimming upstream in rivers.  There are 28 genera and approximately 335 species, found primarily in the Indo-Pacific and Eastern Central Pacific oceans in tropical and warmer temperate areas.  They are primarily herbivorous, with large males grazing and maintaining plots of algal turf on and near coral reefs, but many are also omnivores, feeding on small crustaceans.  Many damselfish species can be quite aggressive, particularly those belonging to the subfamily Pomacentrinae.  Thus it is important to keep this in mind when considering aquarium tank mates, especially if the damselfish is an older, larger specimen.  However two exceptions that are fairly docile are species of the genus Chromis (one of which I’ve cataloged and will post on later), and clown, or anenomae fishes.  The scissortail damselfish is found in the Eastern Pacific, from the northern Gulf of California to northern Peru, including the Galapagos and Cocos islands.  They school in open water above the coral reefs and rocky areas where they live, feeding on zooplankton and often intermingling with king angelfish, another species recently cataloged. They are not as strongly territorial as other damselfishes in the area are. They are almost invisible in the darkness of deep water but for its brilliant post-dorsal white spot which gives the illusion of glowing in the dark.

Scaridae (parrotfishes) Nicholsina denticulata loosetooth parrotfish

The generic name for this fish species was given for J.T. Nichols, 1920-1941, a curator at the American Museum of Natural History. Almost all of the species in this family have teeth fused into a hard beaklike structure enabling them to crush the coral and rocks from which they scrape algae.  One exception being the loosetooth parrotfish, whose teeth are unlike those of their confamilials.  This species is found in the Eastern Pacific from the Gulf of California to northern Peru and the Galapagos Islands. They are abundant in shallow coastal areas, especially in rocky coasts with macroalgae.  They can be solitary or swim in loose schools, and feed by scraping or breaking off chunks of the reef and digest the algae that grows within, or they feed directly on algae.  Parrotfishes are actually responsible for some of the sand that creates beaches and small islands, biting off pieces of rock and coral with their jaw teeth, chewing the pieces with their throat teeth and excreting the byproduct.  For a look at the species that is ostensibly the best at making sand, check out these really odd looking humpback parrotfish on this fantastic BBC video.  These fishes exhibit beautiful colors, and change their colors as they develop from young to adult.  Most species in the Scaridae also exhibit sequential hermaphroditism, changing sex as they mature, mainly from females to males.  These life histories, combined with the ability of many species to mimic colors of other species as juveniles, makes it sometimes difficult to determine species identifications.  Fortunately for me, most of the specimens in our collection have already lost their carotenoid colors, leaving only the color patterns provided by melanins, and by guanine crystals under some fishes’ skins.

tiger snake eel Myrichthys tigrinus Family Ophichthidae (snake eels)

Most people interested in fish are familiar with the sinister looking moray eels.  The closely related but much less frightening snake eels are a fascinating group.  One of the differences between morays and snake eels is their tails: Species in the family Muraenidae (morays) have broad, flattened tails, whereas snake eels have tapered, pointed tails.  Many have only vestigial fins, lending to their snake-like appearance and aiding in their burrowing lifestyle.  It is said that if swallowed whole they try to burrow out of the attacker’s body, and have been found buried in the larger fish’s flesh.  Snake eels are found on sandy bottoms of coral reef areas and muddy bottoms of grass flats to 200 feet depth.  The primarily nocturnal snake eels make burrows in the soft bottom tail first, and hunt for crustaceans, octopuses and small fishes in and on the sand. They have no commercial value although they are eaten by individual artisanal fishermen. Several snake eels are rather attractive as you can see on fishbase, many species in the family make good aquarium pets (but make certain to keep a tight cover on the aquarium as they are known to slither out in search of food), and are said to be bold and easily approached by divers (in which case maybe you won’t need the rotenone?

Fish Stories: The Elusive Swamp Eel

OSUM Study Monopterus alba

Picture of OSUM Study Specimen Monopterus alba (you’re not missing much, the cryptically camouflaged live specimens are normally not much more colorful!)

The Asian Swamp Eel is known to occur as a native fish species throughout much of southeastern Asia, including India, China, Japan, Malaysia and Indonesia.  There are reports of sightings of Asian Swamp Eels from several other countries in the vicinity including Australia.  The species is now established in several countries outside their native range in western Africa, South, Central and North America.  Populations are established in the United States; first in Hawaii, then in Georgia and most recently in Florida.  Possible modes of invasion include escape from aquaculture ponds where the eels are raised for food.

Swamp eels are known as one of several fish species named as a source of a nematode parasite that causes human gnathostomiasis.  The roundworm nematode must be ingested by the human host for successful infestation, but thoroughly cooking or freezing the intermediary host will kill the parasites.  Thus it is inadvisable to use the swamp eels for sushi!

Other than being a host for a human parasite it is currently thought that the Asian Swamp Eel is relatively benign as far as their impact on local ecosystems, unlike some other more deleterious invasives.  Although they are recognized as a pest neither the federal nor state regulatory agencies in the U.S. restrict the possession or culture of the Asian Swamp Eel.

According to the USGS the potential exists for establishment across the southern U.S. since they can survive relatively cold climates.  Asian Swamp Eels are primarily nocturnal, making their movements hard to detect as well as difficult to prevent.  They prey on small animals like fish, crayfish, worms, snails and aquatic insects but also feed on detritus.  One of several characteristics that enable this species to invade new territories is their ability to breath air, allowing them to occupy ephemeral water bodies, burrowing into wet earth during the dry seasons, and to move across land (it is likely that the swamp eels behave like lungfish in creating a cocoon of mucous that serves to retain moisture, since they are able to secrete copious amounts of of the slimy material).  Given they are air breathers application of chemicals like Rotenone that removes oxygen from the water would not be an effective control.

The skin of the larvae is highly vascularized so the young individuals use their large pectoral fins to pass water over their skin.  As the larvae mature they lose the pectoral fins as well as permeability of most of the external tissues.  Adults retain the vascularity of the skin of their mouths and throat linings and develop an air breathing apparatus called the suprabranchial, or labyrinth, organ.  The epithelial material of the mouth and pharynx develops from the first gill arch, while the labyrinth organ develops from the dorsal ends of the remaining gill arches; thus the organ sits atop the lower gill arches.


Gourami with gill cover raised, note untransformed lower gill structures below transformed labyrinth organ

The gill opening for Asian Swamp Eels consists of a single slit across the throat, so they must need to keep their head off the bottom in order to breath underwater through the gill slit.  But of course they are able to breathe through their mouths, so the only time the gill slit would be used is when they are eating or need to expel objects from their gills.

OSUM Study Monopterus alba gill slit

Picture of OSUM Study Specimen Monopterus alba, focused on gill slit

 Regarding reproductive behavior the males build a large “bubble nest” from their saliva and plant matter in submerged aquatic vegetation in shallow nearshore areas, and guard the eggs and young until they are ready to leave the nest.  They share this behavior with some other fish species such as gouramis, snakeheads and bettas (which, interestingly, also have labyrinth organs).  This is one of several fish species that naturally exhibits sequential protogynous hermaphroditism; starting out as a female, passing through an intersexual stage, and transforming to a functional male.

Other distinctive characters that typify the swamp eel Family Synbranchidae include the lack of all fins excepting the dorsal, caudal and anal fins that are reduced to skin folds, small, sometimes skin-covered eyes, and the lack of a swim bladder, scales and ribs.  These characters render the swamp eels well suited to their secretive lifestyle, slithering across the mud, through tunnels, canals and hiding in crevices and dense mats of aquatic plants.

 OSUM Study Monopterus alba head

Picture of OSUM Study Specimen Monopterus alba, note small, skin covered eyes

Big Minnows?

Not an Oxymoron

There are some concepts that fit the definition of an oxymoron, but unbeknownst to the majority of the non-ichthyologically educated public, the phrase “Big Minnow” does not qualify for that concept.  When most of us think of minnows we think of very small fish, but often the fish species that come to mind don’t fit the proper definition either.  Fishermen  frequently speak of “minnies” as any small fish that is used for bait, but let me take an opportunity to tell you some of what I’ve learned about minnows.  First of all, the scientific definition of minnows limits the group to the fish family Cyprinidae, so all those little bass, darters and sticklebacks may be used for bait, but they are not minnows.

Next, allow me to elaborate on the idea that not all minnows are small: Did you know that the minnow family includes common carp?  Oh, and there’s a subject that needs some correction as well!  You see, carp are not only the bottom feeding scavengers that the term conjures up in our minds, but instead include a diverse assemblage of fish species such as Koi, Goldfish and “Asian Carp”, a term that begs for explanation in of itself.  We’ll return to that area of controversy later in this post.

Pikeminnows are the largest native North American minnow species, reaching six feet in length with a maximum recorded weight of about 40 pounds.  The biggest minnow species at up to 10 feet long and almost 140 pounds is the Giant Barb Catlocarpio siamensis, found in southeast Asia where it is sometimes kept in ponds for food.

Ptychocheilus umpquae 74564


OSUM 74564 Ptychocheilus umpquae Umpqua pikeminnow



Catlocarpio siamensis Giant barb (photo from National Geographic)

Speaking of Asia, let me take a few sentences to flesh out the term “Asian Carp”.  Recently, sensational news reports revealed invasive fish species now found in several tributaries to the Mississippi River that are included under the umbrella term “Asian Carp”.  It is a fact that all carp originally came from Asia and parts of Europe, but the carp that are currently most notorious are actually two species, the Bighead Carp and the Silver Carp.  Two other species, Grass Carp and Black Carp, are also relatively recent invaders, but the Common Carp has been here since the mid-1800’s when they were imported by entrepreneurial European farmers in an effort to continue their husbandry of the fish that they had raised in ponds back in their homelands.  Unfortunately the U.S. Department of Conservation decided that a little bit of a good thing would only be better if it were increased, so they transported Common Carp in rail cars across the United States.  Common Carp in the wild are bottom feeders and require removal of the “mud vein” to make them palatable, so the invasive fish became a nuisance since they actually muck up the waters and decrease aquatic habitat quality.  Fast forward to the past 50 years when another well-intentioned effort resulted in disaster:  Overflowing Bighead and Silver Carp hatcheries in Missouri introduced those species to the Missouri River from where they proliferated and now represent a substantial portion of the fish fauna in much of the Mississippi River mainstem and watershed.

Silver Carp2 from the Spoon River IL summer 2007 by NT

Hypophthalmichthys molitrix, Silver carp (photo by Brian Zimmerman)

Now, most minnows are indeed small, and the smallest minnow, by the bye, is also the smallest known fish species in the world (Paeodocypris progenetica) for which there is no common name that I could find.  Found only in Sumatra, the species matures at about 10mm long.  For comparison the smallest minnow in North America is relatively a whopper at 38mm.  Minnows are a very well researched group of animals and there is a lot more to talk about;  for example going into more depth I could tell you that the only true minnows are the fishes placed in the subfamily Leuciscinae, or that true minnows only have teeth in their throats…but we’ll leave those tidbits for another blog.