Okay, this post has been delayed again. It's been an unusual week, is all I can say. I'd tell you all about, but I have very good reasons to believe that that would be extremely dull.
In earlier posts, I have ranted in a rather esoteric manner about my distaste with the commonly recognised fish order "Perciformes", really a random multi-paraphyletic assemblage of the more generalised members of the clade Percomorpha. In the recent partial reclassification of the Percomorpha by Li et al. (2009), the name "Perciformes" was ditched entirely, and the clade containing the family Percidae was instead called Serraniformes (suggesting, offhand, that some sort of taxonomic karma is dooming this taxon to be associated with confusing names - the family Serranidae as commonly recognised itself seems likely to be polyphyletic, and a number of "serranids" are not guaranteed Serraniformes). But even before the Perciformes of common use were recognised as a wastebasket assemblage (if, indeed, there ever really was such a time), Percidae was always a slightly odd choice for the type family. The Percidae, the perches and darters, are not particularly average Perciformes.
Among the percomorphs, percids are unusual for one main reason - they're almost entirely freshwater (a few European species stray into brackish waters, but only one species - Sander marinus, the estuarine perch of the Black and Caspian Seas - is a permanent resident in them). While the percomorphs have achieved true world dominance in the upper parts of the ocean, including the vast majority of coastal and surface-pelagic fish species, they have never made such significant inroads into fresh water. A few percomorph lineages have been very successful in fresh water, such as the Cichlidae, the Anabantiformes and various members of the Smegmamorpha*. But in contrast to their surface-marine monopoly, percomorphs have to share dominance of the fresh-water environment with members of the clade Otophysi - Cypriniformes, Characiformes and Siluriformes.
*No, honestly, it's a real name.
The Serraniformes also include the Trachinidae (weevers), the circum-Antarctic notothenioids and the majority of what were the Scorpaeniformes. Relationships within the Serraniformes are yet to be hammered out, but the Percidae probably divide from the others reasonably basally. Ten genera of living Percidae are currently recognised, with more than two hundred species. Phylogenetic analysis of the family by Sloss et al. (2004) recognised three main clades of unresolved relationships - the Holarctic genus Perca, the mostly Eurasian clade of Gymnocephalus plus Luciopercinae (genera Romanichthys, Sander and Zingel, with three species of Sander in North America), and the North American clade of Etheostomatinae (Ammocrypta, Crystallaria, Etheostoma and Percina). [The tenth genus includes the single uncommon species Percarina demidoffi of rivers running into the Black Sea, and was not analysed by Sloss et al. due to lack of material. Percarina was previously classified in the possibly non-monophyletic Percinae* with Perca and Gymnocephalus and differs from most other Percinae in spawning in brackish waters, so establishing its relationships would be very interesting.] While the greater phylogenetic disparity of Percidae is concentrated in the western Palaearctic and the family is believed to have originated in that area, the greater diversity of species is definitely found in North America. Well over two-thirds of percid species belong to the Etheostomatinae, with the greater part of those in the genus Etheostoma (which, however, may not be monophyletic).
*Though the non-monophyly of Percinae found by Sloss et al. is in contrast to their breeding behaviour - Percinae differ from other percids in laying their eggs encased in long gelatinous strands, while Luciopercinae and (ancestrally) Etheostomatinae are broadcast spawners.
Human interest in the Percidae (as with most matters, really) has usually been related to one of two things - eating or sex. The larger percids of the "Percinae" and Luciopercinae are widely caught for food, and the European perch Perca fluviatilis has been introduced to many localities outside its native range such as New Zealand for the amusement of anglers. Some percids, such as the walleye Sander vitreus, have been recorded reaching lengths of over a metre (though such sizes are, of course, exceptional - a more average walleye would be about twenty centimetres). Species of the Etheostomatinae, known as darters, are not targets of fishing - members of this subfamily (as well as some species of Luciopercinae) are smaller than other percids, less than ten centimetres in length*, and wouldn't offer much in the way of eating. Still, darters more than make up their interest in the other regard of sex. They show a wide diversity of breeding behaviour, from broadcast spawners to some that bury their eggs in sediment or gravel to species that lay their eggs safely hidden on the underside of rocks. Other species may glue their eggs to vegetation (Winn, 1958a, b). During the breeding season, most (but not all) darters move from deeper to shallower waters (many species favour riffle areas) where the males usually establish a breeding territory (as reported by Winn, 1958b, the presence of other males seems to be required to incite the successful establishment of a territory - solitary males tended to lose interest in a potential territory and wander off). Some darter species are fairly relaxed about their territories and only fend off males of their own species, but other darters may be decidedly pugnacious and attack just about anything that moves. Challenging males approach each other with fins held high, and their colours will often become brighter. They may circle each other and butt or bite at each other's tail regions. After a male has mated with a female and she has laid her eggs, he may or may not remain in the area to guard them. Experiments have shown that if the eggs are removed or replaced, the male continues to guard the same spot, so it is the territory that induces guarding behaviour rather than the presence of eggs. Hybrids have been recorded between a number of darter species and seem to be not uncommon, especially where species have been spread outside their native range (Stauffer et al., 1995).
*As a corollary of their smaller size, it is worth noting that darters (and the smaller Luciopercinae) also lack swim bladders.
REFERENCES
Reeves, C. D. 1907. The breeding habits of the rainbow darter (Etheostoma cœruleum Storer), a study in sexual selection. Biological Bulletin 14 (1): 35-59.
Sloss, B. L., N. Billington & B. M. Burr. 2004. A molecular phylogeny of the Percidae (Teleostei, Perciformes) based on mitochondrial DNA sequence. Molecular Phylogenetics and Evolution 32 (2): 545-562.
Stauffer, J. R., Jr, J. M. Boltz & L. R. White. 1995. The fishes of West Virginia. Proceedings of the Academy of Natural Sciences of Philadelphia 146: 1-389.
Winn, H. E. 1958a. Observation on the reproductive babits of darters (Pisces-Percidae). American Midland Naturalist 59 (1): 190-212.
Winn, H. E. 1958b. Comparative reproductive behavior and ecology of fourteen species of darters (Pisces-
Percidae). Ecological Monographs 28 (2): 155-191.
