Fish foraging periodicity correlates with daily changes of diet quality

We tested the adaptive feeding hypothesis of Taborsky and Limberger (1980; Pubbl. Staz. zool. Napoli (I: Mar. Ecol.) 1: 143–153) by comparing two populations ofParablennius sanguinolentus (observed ca. 20 km north of Trieste, Italy, and near Calvi, France, during August and September 1989), each of which fed on different algae: turf and sea lettuce (Ulva lactuca). Turf energy peaked in the afternoon,U. lactuca energy around noon. In both fish populations, feeding paralleled the energy content of their food source, which is strong evidence for the adaptive feeding hypothesis. Turf feeders took an average of 2 to 7 times more bites in the afternoon than at other times of the day, whereasU. lactuca feeders bit 1.4 to 15 times more often around noon. We checked for chemical components of algae, but our data did not suffice to reduce the diel pattern of energy content to the short-term distribution of either starch, protein or ash.