Yellow perch and European perch

In Wisconsin and other Midwestern states, a fish fry means a perch fry. There is no tastier pan fish. Throughout its range, the perch is a popular sport fish, put up a good fight, and are good to eat.  Friday night still means time for a fish fry. Fridays were a day of abstinence from meat and fish were not meat simply because they were cold blooded.  The Irish, Polish, and German immigrants settled in the Midwestern USA and knew how to fry large quantities of fish.  

Friday fish fry.   Photo by Loco Leprechaun.

After a serving of fried perch, one has to wonder “Why eat anything else?”  The perch of the Midwestern fish fry are Yellow Perch Perca flavescens Mitchill, 1814.  Students and anglers alike appreciate the Yellow Perch because it is so easy to catch and easy to identify.  Yellow Perch are yellow with 5-7 dark vertical bands that fade gradually near the belly.  The two dorsal fines are separate.  The large spiny dorsal fin has 13- 15 spines and a soft second dorsal fin has 12 to 15 years plus 1 or 2 spines.  There are spines on the opercula tip and the caudal fin is forked.  Yellow Perch have a rough texture from ctenoid scales.  Yellow Perch remain active all winter long and provide year-round angling opportunities.  And the biology of the Yellow Perch has been well studied in numerous systems.  Yellow Perch can dominate many small lakes and thereby compete with other fishes for food.  In these cases, they typically outcompete salmonid species.  Yes, other fish may not like the Yellow Perch as much as we do. 
 

Yellow perch illustration by Val Kells. © Johns Hopkins University Press

 But the Yellow Perch are not the only perch -- there are three species of perch in the genus Perca.   The European Perch (Perca fluviatilis Linnaeus, 1758) are identical to Yellow Perch.   European Perch are distributed across most of northern Europe, eastern Russia, the British Isles and as far south as the Caspian Sea.  The national fish of Finland is the European perch. They do reach larger sizes, with jumbo perch often exceeding three pounds in weight. In January 2010 a perch with a weight of 3.75 kg (8 lb 4 oz) was caught in the River Meuse, Netherlands. 

European Perch Perca fluviatilis   Photo by G. Schmida Source

Therefore, any curious thoughtful student must ask, “how did these two similar perches come to exist?”  The process is called speciation.  Speciation is a lineage-splitting event that produces two or more species.  The event can be any event that separates subgroups such that the populations diverge due to different selective pressures and experiences different random events.  Many generations of such natural selection and restricted gene flow give rise to two unique species.   In the case of the speciation in the perches, geographic isolation due to the separation of the continents was the obvious cause. 

Many glacial advances and retreats have occured over the last 2.5 million years.  This map shows one time period of the extent of glaciation during the Pleistocene.

                                                                                              

The species may still have the ability to cross breed, which raises the question as to whether to to are distinct species or subspecies.   I like to think of them as incipient species.   Time is needed for reproductive isolating mechanisms to develop.  Speciation requires that the two incipient species be unable to produce viable offspring together or that they avoid mating with members of the other group.

Distribution of Yellow Perch in North America.   Source: roughfish.com

When we examine the broad geographic range of the Yellow Perch, the student of Ichthyology will wonder just how similar Yellow Perch are over this distribution.  The patterns of genetic diversity are related to connectivity, dispersal, and distribution   There are northern postglacial, southern glacial refugia and coastal populations that have limited opportunities for connectivity and dispersal, each of which have diverged genetically  and are more distantly related though distinct from the European Perch (Sepulveda-Villet and Stepien 2012).  Patterns do not always conform to the isolation-by-distance hypothesis.  Even within single bodies of water homing behavior and spawning group fidelity may result in fine-scale genetic differentiation. In Europe, the southern refugia diverged from the founder populations.

Continential configurations and connections during the mid-Cretaceous (88 MYPB, Carney and Dick 2000).

Divergence between the two species began when the continents separated.  During the Cretaceous, North America was divided by a large inland sea.  North America remained connected to Europe through Greenland and the Faroe Island in the east, and to Siberia in the west. Europe and North America began to separate during the Eocene (53-57 MYBP). While we cannot be sure where the ancestral percid fish originated,  Carney and Dick (2000) hypothesized that Perca originated as early as the Oligocene (30MYBP) when North America and Europe were still connected across the North Atlantic.  Earliest Perca fossils in western Europe were found in deposits dated to 26 MYBP.       Speciation was via the vacariant event of separation of North America and Eurasia due to opening of the Atlantic Ocean.   Millions of years have led to the present day species and the Friday fish fries made possible by the Yellow Perch. 

  

References

Brown, T.G., Runciman, B., Bradford, M.J., and Pollard, S. 2009. A biological synopsis of yellow perch (Perca flavescens). Can. Manuscr. Rep. Fish. Aquat. Sci. 2883: v + 28 p.

Carney, J.P., and T.A. Dick. 2000. The historical ecology of yellow perch (Perca flavescens [Mitchell]) and their parasites.   Journal of Biogeography 27:1337-1347.  http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2699.2000.00511.x/abstract

Fisch-Hitparade (in German). 2010.  http://www.fisch-hitparade.de/fischhitparade/fang_anzeigen.php?fid=9854  Retrieved 30 November  2017.

NesbØ, C.L., T. Fossheim, L.A. VØllestad, and K.S. Jakobsen.   1999.  Genetic divergence and phylogeographic relationships among European perch (Perca fluviatilis) populations reflectglacial refugia and postglacial colonization.  Molecular Ecology  8:1387-1404.

Sepulveda-Villet, O., A.M. Ford, J.D. Williams, and C.A. Stepien. 2009. Population genetic diversity and phylogeographic divergence patterns of the Yellow Perch (Perca flavescens).  Journal of Great Lakes Research 35:107-119.

Sepulveda-Villet, O., and C.A. Stepien. 2012. Waterscape genetics of the yellow perch (Perca flavescens): patterns across large connected ecosystems and isolated relict populations.   Molecular Ecology 21:5795-5826.