Meeting Abstract
Fish swimming is grouped into two main categories: body-caudal fin (BCF) and median/paired fin (MPF) locomotion, with the former being much more thoroughly investigated. Gymnotiform swimmers, or “knifefish”, fall into the latter group, using an elongated anal fin to produce thrust via ribbon-like undulations. Knifefish are found throughout Gymnotiformes and in one family of Osteoglossiformes. Since these orders are not closely related, convergence on gymnotiform swimming may be adaptive for both groups. While theoretical frameworks suggest that knifefish are highly maneuverable, poor accelerators, and inefficient sustained swimmers, little is known about the actual performance of fish from these groups. A previous study on one species (Xenomystus nigri) suggests that their ability to perform escape responses is comparable to that of BCF swimming teleosts despite their potential morphological constraints; however other swimming performance measures have rarely been tested across species. To better understand the costs and benefits associated with gymnotiform swimming, we investigated the performance of a BCF swimmer, the giant danio (Devario malabaricus); a pure gymnotiform swimmer, the black ghost knifefish (Apteronotus albifrons); and two Osteoglossiform knifefish which utilize varying degrees of BCF and anal fin undulations, the clown (Chitala ornata) and African brown (X. nigri). We captured escape responses, recorded sprint speeds, and gathered cost of transport data on 5-8 individuals from each species. Preliminary size-corrected maximum sprint speed analyses suggest that the BCF swimmer is faster than all knifefish studied. Further analyses, along with cost of transport and escape response results, will provide a better understanding of the transition to this unique locomotor mode.
