Abstract
Feeding preference of Chironomus crassicaudatus 4th instars when fed on 5 algal species, Anabaena flos-aquae, Botryococcus braunii, Lyngbia cf. aeruginosa, Microcystis sp., and Scenedesmus quadricauda was studied under laboratory conditions. The various algal species were mixed in pairs at 1:1 ratio (fresh weight) to create 10 possible test combinations. The larvae were allowed to feed individually for 8 h on each algal mixture in tissue culture plates having 4 replicates. Four identical algal mixtures were simultaneously used without larvae as controls. After feeding, larvae and excrement were removed, and remaining algae from feeding trials and controls were fixed with Lugol's solution; the final ratio of algal species in each mixture was determined microscopically. Feeding preferences of C. crassicaudatus early 4th instars, in descending order, was L. cf. aeruginosa, A. flos-aquae, B. braunii, Microcystis sp., and S. quadricaudata. To evaluate algal digestibility, larval excrement was collected and the proportion of live and dead cells was determined by microscopic observations with the use of visible and ultraviolet light (epifluorescence). Anabaena flos-aquae and L. cf. aeruginosa were the easiest to digest, followed by Microcystis sp. and S. quadricaudata, whereas no digestion of B. braunii was observed. Cultures of larval excrement revealed the presence of some viable cells of all 5 tested algal species.