Feeding-Habits of the Bayou Darter

From March 1986 to August 1987, we investigated the trophic ecology of the bayou darter Etheostoma rubrum, an endemic of Bayou Pierre, Mississippi, that is federally listed as threatened. Twenty‐four prey taxa were identified from 440 bayou darters (standard length, 15–52 mm). Five prey taxa were dominant in terms of number and weight: chironomids, simuliids, Hydracarina, and, collectively, ephemeropterans and trichopterans. Chironomids constituted the greatest portion of the diet by weight and number (39 and 41%), followed by simuliids (20% by number) and Hydracarina (22% by number). Ephemeropterans and trichopterans had their greatest importance during summer and fall. Seasonal variation in the diet was evidenced by relative occurrence of prey in stomachs and significant differences in feeding intensity across months. Feeding intensity, as measured by a relative fullness index (RFI) and monthly mean numbers of prey, peaked during April 1987, when the RFI reached 3% and the average number of prey per stomach was 125. Analysis of diet across seven size intervals indicated that bayou darters in the 30–34‐mm range had an ontogenetic shift in diet. No such shift was detected for age‐0 fish, although we sampled only fish greater than 15 mm in length