Is the Pirate Perch Really a Ghost? A Look into the Mechanism of Chemical Camouflage, by Kevin Eliason

The pirate perch isn’t a pirate and it isn’t a perch, but it may be a ghost. The pirate perch (Aphredoderus sayanus) is a fish that lives throughout much of the southern United States and Mississippi drainage. The pirate perch is a monotypic family, sayanus being the only species. Page and Burr describe the species having: a short deep body often 3-4 in long, large head, large mouth, anus and urogenital opening between branchiostegal membranes(Page and Burr 2010)(fig 1). The pirate perch lives in backwaters and swampy areas, often around vegetation and over mud bottom. Pirate perch are prey for birds, fish, and water snakes. In order to avoid predation pirate perch often stay close to woody debris for protection and are nocturnal to help avoid site based predators. The pirate perch in turn feed on primarily small freshwater shrimp and insect larvae but are generalist feeders (McCallum 2012). Pirate perch also use a form of chemical camouflage/ chemical deception to potentially avoid predation and enhance predation on chemical sensitive prey (Resetarits and Binckley 2013).

You may be asking yourself, “What is this chemical camouflage?”  In the case of pirate perch, the mechanism of camouflage isn’t exactly known, however, it is believed that pirate perch have evolved it as a novel way of hiding from prey. Dr. Resetarits explored the capabilities of chemical camouflage in pirate perch using artificial ponds in which pirate perch were put in adjacent ponds with sunfish and ponds without fish as a control. Dr. Resetarits found that beetles and tree frogs both actively avoided ponds with sunfish, but no significant difference between pirate perch ponds and controls were observed (Binckley and Resetarits Jr. 2003; Resetarits and Pintar 2016). Resetarists proposed three possible mechanisms for this camouflage: Distorted or mixed signals, mimicry of a non-threatening organism, or simple cloaking and lack of signal. I will explore each of these methods, and together we will try and uncover the ghost of the fish.

Figure 1. Aphredoderus sayanaus Image Credit: Ellen Edmonson and Hugh Chrisp

First, distorted and mixed chemical signals; a mechanism would imply that the pirate perch still emits a chemical signal but it doesn’t register the same as other fish. This method is the most probable, in my opinion, based on Resetarists’s findings as the number of beetles and tree frogs were generally lower then controls, just not at a significant level. This apparent trend may imply that some sense of predation was still occurring at the ponds with pirate perch. This would lead us to believe that it is still emitting a chemical signal, but not easily detected.

Second, mimicry of a nonthreatening organism. This method is used often in nature as a defense against predators. Some familiar mimics may include coral snake/milk snakes and stick bugs. This mimicry is used as a defense against predators to either hide in plain site or imitate a dangerous organism. There are also aggressive forms of mimicry like freshwater mussels whom lure fish in with their mantles shaped like small fish and insects in order to inoculate them with young. Parasites are also well known to use mimicry to trick hosts into eating them. If pirate perch utilized this method it would be likely that they are mimicking something that is either not a fish or as a nonthreatening fish, like a sucker or non-insectivorous fish. I believe mimicry to be the least likely of the three proposed but also one of the hardest to prove. Some potential issues are if mimicry is the mechanism used, what are the pirate perch mimicking and how does that mimicry deceive different types of prey items.

The third and final mechanisms is cloaking of the chemical signal. This mechanism would insinuate that the pirate perch has evolved to not exhibit the chemical markers that other fish have. This method is also very probable as the true mechanism of pirate perch’s chemical camouflage. This is probable due to evolution being easier for pirate perch to lose their chemical signature or produce a chemical signature that that doesn’t bind or respond to the normal receptors. Also, being a monotypic species it is possible that lacking chemical signatures has been an ancestral trait that only survives in the pirate perch.

In conclusion, I believe that out of the three methods it is most likely that the pirate perch achieves chemical camouflage using distorted or mixed signals. I support this belief based on Resetarits’s findings with beetles and tree frogs. Also, It is unlikely that beetles and tree frogs receive signals in the exact same way, this makes me believe that a distorted signal is more likely then cloaking which may not be effective on all types of organisms. In addition, it is also possible that the mechanism used by pirate perch may not fit neatly into one of these three categories. Rather, the mechanism is a little bit of two or all three mechanisms. This could be achieved by distortion of the chemical signal that may be sensed more like some other organism. Alternatively, it also could be distortion to the point that the sense is overwhelmed and essentially cloaking has occurred. These questions cannot be answered with the current knowledge of the pirate perch. This mechanism, which potentially represents a new evolution in the predator-prey arms race. The pirate perch will no doubt be a subject of returning research as the ichthyology community begins to unravel the mysteries of the pirate perch and its chemical camouflage.

References

Binckley, Christopher A., and William J. Resetarits Jr. 2003. “Functional Equivalence of Non-Lethal Effects: Generalized Fish Avoidance Determines Distribution of Gray Treefrog, Hyla Chrysoscelis, Larvae.” Oikos 102(3): 623–29.

McCallum, Malcolm L. 2012. “Notes on the Diet and Egg Clutches of the Pirate Perch (Aphredoderus Sayanus) from Central Arkansas.” Southeastern Naturalist 11(3): 543–45.

Page, Lawrence M., and Brooks M. Burr. 2010. A Field Guide to Freshwater Fishes: North America, North of Mexico. Second. Boston; New York: Houghton Mifflin.Print.

Resetarits, William J., and Christopher A. Binckley. 2013. “Is the Pirate Really a Ghost? Evidence for Generalized Chemical Camouflage in an Aquatic Predator, Pirate Perch Aphredoderus Sayanus.” The American Naturalist 181(5): 690–99.

Resetarits, William J., and Matthew R. Pintar. 2016. “Functional Diversity of Non-Lethal Effects, Chemical Camouflage, and Variation in Fish Avoidance in Colonizing Beetles.” Ecology 97(12): 3517–29.

Questions about Pirate Perch Aphredoderus sayanus (Gilliams, 1824), by Don Orth

The Pirate Perch Aphredoderus sayanus (Gilliams, 1824) is a small, but distinctive fish.  Coloration is mostly dark brown or olive gray with black speckles and a narrow vertical dark bar on tail fin and under the eye.  Young are dark, almost black.  Breeding adults may be violet or purple, where non-breeding adults are pinkish with dark olive pigments.   It is distinguishable by its shape, coloration, single dorsal fin (usually III–IV, 10–12), serrated preopercle bones, and large mouth with projecting lower jaw.   The lateral line system is best developed in the head region and cutaneous sense organs are also highly developed.   Its most unusual characteristics is the location of the cloaca, or urogenital opening; it is far forward, actually located in the throat region.   Larval Pirate Perch, however,  have a urogenital opening further back like a typical fish, reminding us that “ontogeny recapitulates phylogeny,”  Here I address several frequently asked questions about Pirate Perch. 

Pirate Perch photo by NCFishes.com

Why the name?   Early Ichthyologist Charles Abbot, after observing them eating only other fishes in aquaria, gave the fish its common name, Pirate Perch.  The genus name Aphredoderus translates literally to “excrement throat.”  The species name, sayanus, is a tribute to naturalist Thomas Say as "anus" translates literally to "belonging to."   Although sayanus is the Latinized version of Say, legions of Ichthyology students remember this scientific name by reciting “Say Anus” or “Say Anus Under Throat.”

Where do they live?   These fish occur in rivers of Atlantic and Gulf slopes, Mississippi and parts of the Great Lakes basin.   This familiar coastal plain distribution overlaps with distributions of Redfin Pickerel Esox americanus, Bowfin Amia calva, Tadpole Madtom Noturus gyrinus, and Swamp Darter Etheostoma fusiforme.

Current distribution of Pirate Perch, Source USGS

 Aphredoderus is part of a large monophyletic group, the Paracanthopterygii, a diverse superorder of marine and freshwater fishes that include cods, grenadiers, hakes, anglerfishes, cusk eels, pearlfishes, brotulas, and trout-perches.  Ichthyologist Peter Moyle described this group as the "odds and cods" in reference to the many odd characteristics among the group members.    Ancestors of the Pirate Perch likely emerged in North America after the Cretaceous–Paleogene (K–Pg) extinction event at a time when sea levels where higher and this unique lineage continued to adapt to changing coastal plain habitats as sea levels dropped.      

Why the forward facing urogenital pore?  This odd trait has been a subject of much speculation.  Do the grooves direct ova from the vent into the left and right gill chambers?  Do they incubate fertilized eggs in gill chambers?  Do they deposit eggs in root masses?     Observations on breeding behavior have been made from captive Pirate Perch in aquaria and hatcheries, but until recently no in situ observations have been reported.   One study by Dean Fletcher and others reported that Pirate Perch spawned in underwater tree root masses.   This study was made possible by a remote camera system with infrared lighting.  It was the first documentation of root-mass nesting behavior in any species of North American fish.  Also of  biological interest was the burrowing behavior of dobsonfly larvae and salamanders, which created tunnels through the dense root masses.  The tunnels permit the Pirate Perch to deposit eggs deeper within the root mass.     

Why is there geographic variation in lateral line development?  Lateral line is better developed in populations along the Atlantic Coast compared with Midwest populations.   Ichthyologists George Moore and William Burris described the extensive, complex lateral-line system of the Pirate Perch in 1956.   The exposed neuromasts of the head region occur in a unique ridge formation.  Yet, evolutionary pressures associated with this geographic variation have not been investigated.   

 

Left: Ventral view of cephalic lateral line system by Moore & Burris Copeia 1956:18-20 and Right: Photo of ventral view of head. Photo by Fredlyfish4 Creative Commons.   

What habitats are essential to viable populations?  Pirate Perch are found in lowland streams, rivers, ponds, and backwaters associated with bottom-land hardwood wetlands.   They are more often associated with pools and undercut banks where woody debris accumulations create complex cavities, reduced flow, and trap leaves.   These habitats provide an abundance of macroinvertebrates, an important food source for the nocturnally active Pirate Perch.

What are the threats to Pirate Perch?    Pirate Perch because of their small size are readily eaten by piscivorous fishes (pickerel, bass, and large sunfish) and water snakes.   The complex habitats created by dense vegetation or woody debris accumulations in un-channelized streams and lakes in bottomland hardwoods are essential to sustain Pirate Perch populations.   Ditching, draining and channelization have likely reduced many populations.  Pirate Perch are considered endangered in Ohio, special concern in Iowa, and extirpated from Pennsylvania.  Globally, however, they are rated by IUCN as “least concern.”

Can I eat Pirate Perch?  Although larger specimens can be caught by hook and line, they are not valued as a sport or food fish.  The largest specimens  are only 5-6 inches.  They do persist well in captivity where observations of breeding behaviors were made.    For that reason they are popular among native fish enthusiasts.

Final Fun Fact about Pirate Perch.   Recently,  scientist discovered that Pirate Perch were capable of chemical camoflage such that prey were unable to detect their presence via chemoreception.    How they do this will be revealed only by future scientists who choose to work on this question.