More than 10% of modern fish species are catfish. Does this group support the predictions of the evolutionary, creationism, or intelligent design models?

EVOLUTIONARY MODEL

If evolution is true, the various lineages of catfish should form a nested hiearchy of relationships. They are only expected in the more recent epochs of the fossil record. Speciation in the group should occur through natural processes (such as allopatric speciation) and may result in significant differences within the group.

CREATIONISM MODEL

If the creationism model is correct, then the kind (s) of catfish are equally unrelated to all other types of fish. They should be found since the first week of life on earth. Natural processes such as allopatric speciation should not be responsible for their diversity and variation within the kind is not expected to be significant.

INTELLIGENT DESIGN

If intelligent design is correct, then complex aspects of the natural world, such as speciation, cannot occur in graudal stages. Instead, supernatural influence acting in a specific instant should be evident through "irreducible complexity".

Anatomical and genetic studies indicate a nested hierarchy of relationships between the diverse lineages of the order Siluriformes which is subdivided into more than 30 families and includes more than 2600 species (and perhaps as many as 3,000) (Shimabukuro-Dias, 2004). All catfish form a monophyletic clade and within catfish, there are a number of smaller clades which have been identified. In the Order Siluriformes, the group Loricoidea was an early basal lineage to diverge from the crown group (Sullivan, 2006; Aquino, 2002; Bentacur, 2007; Shimabukuro-Dias, 2004). The superfamily Loricarioidea consists of the families Callichthyidae, Nematogenyidae, Trichomycteridae, Scoloplacidae, Astroblepidae, and Loricariidae and represents the largest superfamilial clade within Siluriformes (Shimabukuro-Dias, 2004).

Outside the oceans, the greatest diversity of freshwater fish in the world occur in the Neotropics, where about 8,000 species reside. Many species are endemic to specific areas and their distribution is best explained in light of the geological events of the Cenozoic involving the uplifts of tectonic plates and the resulting changes in drainage basins (Hardman, 2006). The earliest known fossil catfish date from the Cretaceous but, given that they were already diversified by this time, the origin of catfish is thought to have occurred earlier (Bentacur, 2007). Many catfish species diversified as plate tectonics changed the waterways and the geography of the southern continents. When the Indian subcontinent collided with Eurasia 50 to 45 million years ago, it began the formation of the Tibetan plateau, the largest and highest plateau on Earth (5 million square kilometers and an average height of 5 km). The resulting geologic changes allowed for the speciation of diverse fish lineages endemic to the area, such as the glyptosternoid catfishes (Peng, 2006). More than 50 fish species are endemic to the Maracaibo basin of northwestern Venezuela which was formed by a rising section of the Andes 8 to 10 million years ago. Endemic pimelodid catfish species seem to have diverged from ancestral lineages during the Miocene (Hardman, 2006).

A large number of significant variations occur within catfish. Catfish vary from small fish measuring 16 mm to forms which can reach 5 meters and weigh over 300 kg (Moyle, p. 250;Arratia, 2003). Within the catfish family Clariidae, the evolution of a more elongated (anguilliform) body shape seems to have occurred independently in at least four lineages (Jansen, 2006). Catfish can be carnivorous, omnivorous, or algal scrapers. Members of the family Loricariidae vary in their tooth morphology: they may eat detritus, insect larvae, mollusks, fish, or algae. Blood parasitism is known in 2 species of catfish (in two subfamilies of the family Trichomycteridae). Vandellia is the only vertebrate parasite of humans; it can enter the urethra of those who urinate and attach with spines. Usually it attaches to gills where it parasitizes them. (Arratia, 2003). Some species of catfish produce chemicals for alarm or communication; a number of toxins are made which range from 12 to 324 kDa. (Arratia, 2003). Only two families are primarily marine: Plotosidae (from the Indian Ocean and Pacific) and Ariidae (Bentacur, 2007).

Catfish possess a suprabranchial organ which allows them to extract oxygen directly from the atmosphere and inhabit oxygen-poor waters where other fish could not survive (Jansen, 2006). Some members of the families Loricaridae and Callichthyidae possess modifications of their gastrointestinal tract which allow gas exchange using swallowed air. Some of these fish are obligate air breathers and may travel for short distances over land (Maina, 1998). Accessory breathing structures in catfish include suprabranchial cavities, swim bladder, stomach, intestine, buccal epithelium, and perhaps gill lamellae (Arratia, 2003).

Catfish fins may vary and some fin variations accommodate movement on land, such as catfish of the family Clariidae. The walking catfish (Clarias batrachus) lives in Asian waters which are stagnant, dry frequently, and have dense vegetation. These waters are difficult for fish to inhabit if they can not breathe air (Saha, 2007). The following images are of Loricariid catfish which can wander onto land at night.

An African catfish (Channallabes apus) not only can come onto land, its modified neck allows it to capture prey on land despite the lack of strong pectoral fins. Most of this fish's diet consists of terrestrial insects (Van Wassenbergh, 2006).

Many other catfish possess modified fins. In catfish, the pectoral radials vary in number, may be absent, and some have a pectoral spine. Some catfish can generate their own sounds because the cleithrum and scapulocoracoid (bones of the pectoral girdle) have been modified. A few cases of sexual dimorphism in pectoral fins are known in catfish. Some catfish possess pelvic radials although they are absent in most (Arratia, 2003). Some catfish have a process on the basipterygium which may be well ossified (called the lateropterygium) and used in walking. While most catfish have 6 pelvic rays in fins, some have up to 16. Some can use their pelvic fins to grasp plants, walk on land or incubate eggs. (Arratia, 2003). Catfish vary in the size of the dorsal, adipose, and anal fins. The dorsal and adipose fins may vary in the number of spines and may even be absent.

Catfish skulls vary in thickness: some are very thin while others are very thick. Some catfish skulls possess extrascapular and epiotic bones. Pterotics may be separate or may fuse with pectoral girdle. In some catfish, the sphenotic, prootic, and pterosphenoid bones of the cranium fuse. The skull bones which possess certain foramina (openings) may vary (Arratia, 2003).

Catfish vary in the muscles they possess. In some species, the levator arcus palatine and levator arcus operculi muscles are absent (Arratia, 2003). New muscles are present in some catfish such as the protractor externi mandibularis tentaculi, retractor externi mandibularis tentaculi, retractor interni mandibularis tentaculi, depressor interni mandibularis tentaculi, intertentacularis, muscles of mandibular barbells (M1, M2, M3, M4, M5), muscle of the oral valve, retractor tentaculi, retractor premaxillae, retractor palatine, adductor hypomandibulae, protractor posttemporalis (Arratia, 2003). In some catfish, a single ancestral muscles can be split such as the protractor hyoidei, extensor tentaculi, levator arcus palatine (Arratia, 2003). The locations of the origins and insertions of a number of muscles can vary such as the hyoideus inferior, hyohyoideus abductor, sternohyoideus, adductor mandibulae, extensor tentaculi, adductor arcus palatine, dilator operculi, levator operculi, adductor operculi, and protractor perctoralis (Arratia, 2003). Some species of Clariidae have enlarged jaw muscles which allow them to close their jaws more quickly and thus capture larger, more elusive prey. Within clariid species, varying conditions of this muscle hypertrophy are known (Wassenbergh, 2005).

A number of catfish lineages have developed armor, apparently independent of one another (Geerinickx, 2006). In the family Loricariidae of suckermouth armored catfish, the armor of the skin is composed of odontodes made of dermal bone, covered by dentin and enamel and, attached by either bone or connective tissue. In some species, the odontodes around the opercle are spikelike and muscular contraction can elevate them (Geerinickx, 2006). Some possess dermal armor composed of two longitudinal rows of plates (Shimabukuro-Dias, 2004).

While most teleosts (and basal catfish families such as Diplomystidae and the loricarioid Nematogenyidae) possess a vertical opercle, some groups have modified its position making oblique (loricarioid families Trichomycteridae and Callichthyidae). In others, such as the family Loricariidae, the opercle is no longer attached to the lower jaw and its position is horizontal. One subfamily of loricariids have modified their dermal armor to include spikes around the opercle and have modified opercular muscles to move these spikes in a completely unique manner. The muscles of the opercle are greatly enlarged and have invaded the area formerly occupied by skull bones, creating two functional skull roofs: one set between the brain and the opercular musculature and a superficial skull roof over the musculature (Geerinickx, 2006). Catfish brains can vary significantly.

Catfish vary in the number of vertebrae they possess. Clariids possess from 56 to more than 100, ariids and bagerids vary from 40 to 50, pangasiids 15-29, (Arratia, 2003). In all catfish, the first vertebrae possess a centrum only and are fused to the basioccipital bone of the skull. In all catfish, the centra of vertebrae 2-4 fuse completely and in some species, other vertebrae may also fuse (Arratia, 2003).

The catfish Heteropneustes fossilis has 2 kinds cones, unlike other catfish (Arratia, 2003). Catfish may have as many as 100,000 taste buds distributed over their body (Weichert, 1970, p.716). The catfish Ictalurus punctatus has 200,000 taste buds (Arratia, 2003). Three separate lineages of the catfish family Ictaluridae have independently adapted to cave environments with a loss of eyes, pigment, lateral line organs, and a modification of neural and sensory structures (Wilcox, 2004).
Catfish are part of the Otophysi clade shich are characterized by the Weberian apparatus-a double chain of bones connecting the ear to the swim bladder. Of the 4 Otophysi orders, catfish vary most in their Weberian apparatus (Arratia, 2003). The swim bladder may be reduced or be absent; Weberian bones may have different shapes or be absent. The swim bladders may even be so reduced that it is completely enclosed in transverse processes of vertebrae (Arratia, 2003). In catfish in which the swim bladder is reduced, the Weberian modified: tripodes and scaphia may lack processes and intercalaria may be absent (Arratia, 2003). Catfish can vary considerably in their sensitivity to sound. The size of the utricle can vary; one family Catfish possesses a single large otolith (Arratia, 2003).

While embryonic teleosts can secrete nitrogenous waste as urea, most adults are incapable of forming urea and release nitrogenous wastes as ammonia instead. The enzymes which produce urea (a set of ornithine-urea cycle or OUC enzymes) are not expressed in most adults. However, some species of fish which have adapted to air-breathing, such as the walking catfish Clarias batrachus , express these enzymes as adults as an adaptation to air breathing and drying pools (Kharbuli, 2006).
Chromosome number in the family Callichthyidae ranges from 44 to 92 (Shimabukuro-Dias, 2004).