Direct and indirect effects of fenoxycarb on freshwater systems dominated by Neocaridina palmata (Decapoda: Atyidae) and macrophyte Ceratophyllum demersum.

Few studies have been conducted with regard to the effects of insecticides on population dynamics of shrimps and associated groups such as macrophytes, phytoplankton, microorganisms etc. In the present study, effects of a single application of fenoxycarb were tested using indoor freshwater systems dominated by Neocaridina palmata and Ceratophyllum demersum (Dicotyledons: Ceratophyllales). The no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for the N. palmata, as scaled by liberated chitobiase, were 6.48 μg/L and 27.76 μg/L, and the dose-related effect lasted for 14 days. Results of principal components analysis (PCA) and that of principal response curves (PRC) method showed that the biomass of C. demersum and concentrations of chlorophyll-a were suppressed, while the concentrations of phycocyanin were promoted. Illumina high-throughput sequencing was adopted to determine the diversity of bacteria and fungi in the media. Result of PCA and PRC showed that the fenoxycarb promoted photosynthetic bacteria (e.g. Cyanobacteria and Rhodobacterales) and suppressed groups involved in nitrogen and sulfur the transformation (e.g. Flavobacterium, hgcI_clade, Cystobasidium, Rhodotorula and Rhizobiales). Promotion in pathogen such as Pseudomonas and Cercozoa and suppression in beneficial taxa such as Novosphingobium and Rhodotorula were also sighted. Result of study suggested a water quality deterioration due to fenoxycarb applications.