Feeding Preference of the Rio Grande Silvery Minnow (Hybognathus amarus)

The Rio Grande silvery minnow (Hybognathus amarus) was historically the most abundant fish in the Rio Grande Basin. However, populations have been declining to the point of being listed under the Endangered Species Act. Potential causes for the decline have been studied, yet little attention has been paid to food resources. This study had three objectives: (1) Determine whether larval fish show a substrate preference when foraging. (2) Determine whether larval fish have a diatom preference when presented with 15 diatom species over six feeding trials. (3) I investigated the possibility of training/conditioning H. amarus to feed on natural food sources (diatoms) and observe conditioning response (reaction time to feeding). I found no difference between substrate preference (p = 0.26). Results for feeding trials 1, 2, and 3 revealed a preference for Nitzschia palea (p < 0.01). Trial 4 revealed a preference for N. paleaformis (p < 0.01). Navicula veneta was the preferred diatom species in feeding trial 5. Nitzschia cf. intermedia was preferred in trial 6 (p < 0.03). Results from these feeding trials proved that H. amarus larvae learn quickly and can be trained to feed on diatom cultures after only one 30-min exposure. Pre-conditioned H. amarus arrived at diatoms cultures in 49 sec ± 39 sec compared to non-conditioned H. amarus, which arrived at diatom cultures at 250 sec ± 550 sec.