DEFORMITIES IN CULTURED CHIRONOMUS-TENTANS LARVAE AND THE INFLUENCE OF SUBSTRATE ON GROWTH, SURVIVAL AND MENTUM WEAR

Effects of four substrates (shredded paper towelling, coarse sand, fin e sand, and silty clay) on growth, survival and mentum wear of Chirono mus tentans larvae were investigated in the laboratory. Three categori es of mentum wear were defined: minimal, moderate and substantial. The number of larvae with worn mentum teeth did not differ in any of the four substrates. However, the number of larvae with minimal wear of th eir teeth was significantly different among the substrates and was in the order coarse sand > shredded paper towelling > clay/silt > fine sa nd. Mentum deformities were observed in the cultured larvae, presumabl y because of inbreeding and not the effect of treatment. Differences i n biomass and survival of larvae among the substrates were not signifi cant (p<0.05), however, there was a trend for lower survival in the sa nd substrates. These findings suggest that shredded paper towelling is the most suitable reference substrate. The occurrence of natural abno rmalities must be considered when using chironomid mouthpart deformiti es as an index of environmental degradation.