An Investigation of the Utility of Feeding Angles Among Lake Malawi Rock-dwelling Cichlids (Teleostei: Cichlidae)

Image analysis was used to measure feeding angles of Labeotropheus trewavasae, Labeotropheus fulleborni, Melanochromis auratus, Metriaclima zebra, Petrotilapia spp., Pseudotropheus c.f. elongatus, Tropheops tropheops, and Tropheops gracilior videotaped in Lake Malawi. Petrotilapia spp. fed on vertical, slanted, and horizontal slopes, T. gracilor grazed on vertical slopes approximately 60% of the time, and the other species spent at least 80% of the time feeding on horizontal slopes. The median feeding angles ranged from 35° to 90°. There are four significantly different groups of feeding angles among the eight rock-dwelling species that were examined: (1) L. trewavasae (35°), (2) L. fulleborni, M. auratus, and P. elongatus (44.8–48.5°), (3) T. tropheops (58.4°), and (4) Petrotilapia spp., T. gracilior, and M. zebra (84.2–90.2°). Feeding angles within a species did not vary with location or differences in fish community structure. Feeding angles were associated with a combination of mouth position and head shape. We hypothesized that feeding angles may be important in differential access to food.

Figure 1.

Median feeding angle for eight species of rock-dwelling cichlids; n corresponds to the number of individuals observed; the number of observations of each individual ranged from 14–29.Those species with the same letter designation exhibited feeding angles that were not significantly different (Kruskal-Wallis, P > 0.05). In total, there were four significantly different feeding-angle groups. A–Labeotropheus trewavasae (mean feeding angle = 35.0°; SD = 5.3; n = 8). B¹–Labeotropheus fulleborni (mean feeding angle = 44.8; SD = 5.3; n = 21). B²–Pseudotropheus c.f. elongatus (mean feeding angle = 44.7°; SD = 7.9; n = 9). B³–Melanochromis auratus (mean feeding angle = 48.5°; SD = 9.8; n = 33). C–Tropheops tropheops (mean feeding angle = 58.4°; SD = 14.3; n = 12). D¹–Metriaclima zebra (mean feeding angle = 84.2°; SD = 10.9; n = 13). D²–Tropheops gracilor (mean feeding angle = 85.9°; SD = 5.0; n = 8). D³–Petrotilapia nigra (mean feeding angle = 90.2°; SD = 6.7; n = 6)