Assimilation efficiency of a temperate-zone intertidal fish (Cebidichthys violaceus) fed diets of macroalgae

We studied assimilation efficiencies of the temperate-zone intertidal fish Cebidichthys violaceus (Girard, 1854) fed in the laboratory on each of the following species of macroalgae: Spongomorpha coalita (Chlorophyta), Ulva lobata (Chlorophyta), Iridaea flaccida (Rhodophyta) and Porphyra perforata (Rhodophyta). Together, these 4 algae make up over 75% of the natural summer diet of C. violaceus. Assimilation efficiency was calculated by proximate organic analysis of food and feces; the amount of ash in food and feces was used as a standard. Depending on the algal species, the fish assimilated 43 to 81% of the protein, 21 to 44% of the lipid, 45 to 62% of the carbohydrate and 31 to 52% of all three classes of organic material combined. These data are the first results showing that a temperate-zone marine fish can assimilate macroalgal constituents. Protein, carbohydrate and total organic material were absorbed more efficiently from rhodophytes than from chlorophytes. Conversely, lipid was absorbed more efficiently from chlorophytes than from rhodophytes. These results are compared with previous work showing that C. violaceus in nature eats more chlorophytes than rhodophytes, but in laboratory preference tests prefers rhodophytes to chlorophytes.