Wednesday, September 2, 2015

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
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.

1 comment:

  1. Thanks for the post! I had never heard of the Pirate Perch before, or a fish with forward-facing urogenital pore. I'm intrigued by the perch's chemical camouflage, is chemical camouflage common among fish?