Frank Huysentruyt

Kinematics of benthic suction feeding in Callichthyidae and Mochokidae, with functional implications for the evolution of food scraping in catfishes

SUMMARY Food scraping has independently evolved twice from suction feeding in the evolution of catfishes: within neotropical Loricarioidea and paleotropical Mochokidae. To gain insight in the evolutionary transitions associated with the evolution towards scraping, we analyzed prey capture kinematics in two species of benthic suction feeders which belong to taxa that are closely related to the scraper lineages (respectively, Corydoras splendens and Synodontis multipunctatus), and compared it to prey capture in a more distantly related, generalist suction feeder (Clarias gariepinus). Simultaneous ventral and lateral view high-speed videos were recorded to quantify the movements of the lower jaw, hyoid, pectoral girdle and neurocranium. Additionally, ellipse modeling was applied to relate head shape differences to buccal expansion kinematics. Similarly to what has been observed in scrapers, rotations of the neurocranium are minimal in the benthic suction feeders, and may consequently have facilitated the evolution of a scraping feeding mechanism. The hypothesis that fish with a more laterally compressed head rely more heavily on lateral expansion of the buccal cavity to generate suction, was confirmed in our sample of catfish species. Since an important contribution of lateral expansion of the head to suction may avoid the need for a strong, ventral depression of the mouth floor during feeding, we hypothesized that this may have allowed a closer association with the substrate in the ancestors of scrapers. However, our hypothesis was not supported by an ancestral state reconstruction, which suggests that scraping probably evolved from sub-terminal mouthed ancestors with dorsoventrally flattened heads.

Redescription of Dolichallabes microphthalmus (Poll, 1942) (Siluriformes, Clariidae)

Abstract As a part of the general revision of anguilliform clariid genera and species, the status of Dolichallabes microphthalmus Poll, 1942, is reviewed, based on morphology and osteology of all available museum specimens. Dolichallabes microphthalmus, the most elongate species within the Clariidae, has been redescribed. Compared to Channallabes apus and Gymnallabes typus, D. microphthalmus is characterized by, in addition to some meristic differences, an elongate body, reduced skull ossification, with (1) one elongate fontanel, (2) antorbital and infraorbital IV the only circumorbital bones present, (3) only one or two suprapreopercular bones on each side, and (4) a sphenotic bearing only one process. Osteological evidence suggests that D. microphthalmus could be considered a paedomorphic clariid.

Development of the osteocranium in Corydoras aeneus (Gill, 1858) Callichthyidae, Siluriformes.

Development in the osteocranium of Corydoras aeneus was studied based on 48 cleared and stained specimens and 10 series of serial sections. Development overall follows the general trends observed in siluriform development, with ossifications appearing as a response to functional demands. Early development of the skull occurs in two distinct phases. In a first phase, several new bony elements, all of dermal origin and related to feeding, appear shortly after yolk depletion (4.4 mm SL). Between 5 and 8 mm SL, developmental priorities seem to shift to size increase of the cartilaginous skull and no new bony elements appear. Finally, a second phase of osteogenesis occurs from 8 to 18 mm SL, in which all remaining dermal and perichondral bones appear. J. Morphol. 2011.