Meeting Abstract

81.4  Friday, Jan. 7  Kissing and scraping: the intramandibular joint in Helostoma temmincki FERRY, LA*; GIBB, AC; KONOW, N; Arizona State University; Northern Arizona University; Brown University Lara.Ferry@asu.edu

The kissing gourami, Helostoma temmincki, is a monotypic, enigmatic tropical freshwater fish, well known for displaying a ‘kissing behavior’— so named because the upper and lower jaws protrude and rotate so that the mouth resembles pursed lips poised for kissing. Such extreme rotation of the tooth-bearing jaw elements is facilitated, at least in part, by an intramandibular joint (IMJ) located within the lower jaw. An IMJ is also present in many fish species that graze on attached foods. Kissing gourami, however, have been described as filter feeders, or large-mouthed ram-feeders. Here, we clarify the mechanism of jaw rotation, and describe the resulting feeding kinematics. We compare the jaw movements used to scrape food with the jaw movements used to capture unattached prey from the benthos and from the water column. Kissing gourami readily scraped attached food, including algal or diatom films, from the substrate and took unattached prey from the benthos. However, they avoided mid-water prey such as Artemia adults/nauplii and commercial food diets, which limited the number of strikes on mid-water prey available for kinematic analysis. During feeding, the IMJ rotated to produce gape angles of ~180 degrees, yielding the eponymous ‘kissing’ posture and placing the teeth in direct contact with the substrate for scraping. Surprisingly little modulation of feeding kinematics was observed between feeding events on the three different food treatments. This may be due to the mechanistic basis of jaw movement, which is modeled here as an extreme modification of the 4-bar mechanism previously proposed for lower jaw rotation.