The European eel (Anguilla Anguilla Linnaeus 1758; Actinopterygii, Anguillidae) is faced with a severe decline (up to 99%) in its natural populations over the last 40 years. Due to the absence of knowledge regarding the exact cause for this decline, a lot of effort is recently put in obtaining a complete artificial breeding program for this endangered, but still globally traded species. Unfortunately, the artificially reared eel larvae are, at present, unable to stay alive for more than three weeks after hatching. Since the larval mortality rate peaks at the onset of active food uptake, and literature regarding the larval feeding capacities, strategies and natural prey preferences is rather scarce, a functional morphological analysis of the feeding apparatus of first feeding larvae is performed. This analysis includes modeling the theoretical bite force by using a graphical 3D-reconstruction of the musculoskeletal system of these extremely small organisms (< 1cm). Based on the acquired 3D data of joints, levers and muscle insertions, as well as muscle data, very small bite forces (10-5 N) are obtained for these European eel larvae. Additionally, preliminary data on kinematics (from video recordings) of jaw and hyoid movements in pre-feeding larvae demonstrates a rather limited ability of jaw movement by both ligaments and muscles. Combining both results, rather small and soft food items are suggested to be preferable in both natural and artificial environments, which appears to be in line with the existing hypothesis that these larvae feed on either small and/or gelatinous prey items in nature (Hydrozoa, Thaliacea, Ctenophora, Polycystenia) and, additionally, may be useful information to optimize the artificial breeding program. |
