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.

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?

An Easy Way to Make Skeletons (or, Impress Your Friends!)

This method commonly used by ichthyologists, forensic scientists and taxidermists uses a scavenger, the dermestid beetle, to remove flesh that would be impossible for the preparator to excise by hand.  There are other methods that would accomplish this goal, such as boiling the carcass or permitting it to rot for a while in water, but  those processes result in disarticulation of the skeleton.   Plus the rotting, or maceration, method is quite putrid.

Dermestid beetles (Family Dermestidae) make great pets! 


Okay, not really, but they are easy to take care of.  The beetle colony needs minimal attention if they are in the proper surroundings.  At most you’ll need to check on them a couple times per week to ensure they have enough food, spritz a little water in the container, and make certain they are not attacked by spiders.  Spiders can devastate a dermestid colony, if you find a spider web in the room kill the spider and its eggs immediately.

A proper habitat for dermestid beetles is dry, shut off from the outside, and has some air flow.  Thus the room we use is ideal with an entrance door that only opens to the outside, thus ensuring that if the beetles did somehow escape their container they cannot enter the rest of the building.  Heat and air flow are provided from a heat lamp and a space heater, they do best in temperatures within a 65-85F range so keep a thermometer nearby.  Escape prevention is easy, simply house them in an aquarium or other container with smooth sides as they are not proficient climbers.  Do make certain the joints of the container are likewise smooth and nothing reaches to the top from inside.


Also make a cover with a screen top that fits tightly to the container, because the adults will fly if it gets warms enough.

When skeletal materials are not at hand the beetles thrive on any sort of meat (chicken livers are cheap and readily available,



but this red hawk made for great fodder.)  A bedding of old newspaper provides a place for hiding and an alternate food source (dermestids also do a number on any cellulose material so don’t set them loose in your home).

Excess flesh is removed from the specimen using a sharp knife.  Care must be exercised to avoid cutting through bones.  The skin and scales, and the gill basket are removed and set aside to dry, thus avoiding destruction by the dermestid beetles.  Once you’ve removed as much flesh as you are able to place the carcass under a heat lamp to dry.  When the carcass has taken on the consistency of jerky, it is ready to feed to the beetles.  Do check on the skeleton at least once per week to note when they have removed almost all of the flesh or they will eat connective cartilage and tendons between the bones.  Manually pick the bugs from the skeleton over their container allowing them to drop back in.  You won’t be able to remove all the dermestids so put the skeleton in a deep freezer to kill the individuals that hide in the crevices.  One more reason the beetles don’t make good pets.  After a couple days your skeleton is ready for exhibit although you may want to clean it up a bit more.



Skin, gill basket (upper right) and skeleton from a recent acquisition.