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 fishbase.de:

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.