Selection and intake of algal species in butterfish (Odax pullus; Labridae)

Abstract

Whether animals increase or decrease food intake with decreasing diet quality, and how they respond to the offer of various diet items, is an active area of research. We tested specimens of the marine herbivorous butterfish (Odax pullus; Labridae) in a variety of no-choice, 2-choice and 4-choice experiments with various algal species. Algae differed in nitrogen and organic matter content as well as in apparent assimilation efficiency. Notably, nitrogen assimilation was related to organic matter assimilation at a slope lower than 1, suggesting an increasing contribution of microbial digestion in the more digestible diets. Food intake was lower, rather than higher, on the lowest quality algae, and higher on the highest quality algae, i.e. the fish did not follow a compensatory intake strategy, but a strategy described in mammals as ‘anticipatory’ where high-quality food is ingested in large amounts when available. Food intake was highest during 4-choice experiments, suggesting that mixing diet items, either to complement various nutrients or to avoid the accumulation of any particular toxin, is an important component of the nutritional strategy in O. pullus.