Investigating the effect of rainbow trout farming on macroinvertebrates functional feeding groups in the Chalous river

Biological evaluation of water resources using macroinvertebrates is one of the most appropriate and most cost-effective methods in order to study human impacts on water ecosystems. Nutrition strategies are a typical feature that reflects the flexibility of species and can be part of a single action in the classification structure of societies. Feeding groups contribute to the metabolism of freshwater ecosystems, including nutrient cycles, reduced particle size (e.g shredder), facilitated the functioning of microparticles, Fungi and yeasts and carrying organic matter in the downstream. The aim of this study was to investigate the distribution of feeding groups of bentic macroinvertebrates as the basis of biological evaluation in the Chalous River as one of the protected rivers in Iran with unique ecological conditions.

Macroinvertebrates were taken using surber sampler (with an approximate area of 0.1 m2 and mesh size of 360 µm) with 3 replicates in 9 stations each season, from June 2015 to March 2016. To compare the abundance of feeding groups in different stations and seasons, the Kruskal-Wallis test was used and a Mann-Whitney test was used to Paired comparison. Simperity tests (SIMPER) were used to determine the feeding groups that had the highest share (participation rate) in the similarity of each station and also the major disparity between the stations.

During the whole period of sampling, 26220 individuals of macroinvertebrates were separated, identified and counted, which were belonged to 3 phyla, 4 classes, 12 orders, 34 Families and 35 Genera. In this study, the highest total abundance of invertebrates in stations 6 and 8 was 15.04% and 16.97% of the different feeding groups, which can be due to the entry of organic matter By wastewater farms before these stations. Suspended solids along with non-eaten foods in salmon farms seem to play an important role in increasing the abundance of bentic macroinvertebrate in the bottom of fish farms. Functional feeding groups of macroinvertebrates in this study included five groups: Collector Gatherer, Collector Filter, Predator, Scraper and Shredder. Results showed that, the abundance of Collector Gatherer in station 8 is higher than other stations. The frequencies of Scraper and Shredder groups showed significant differences with other groups (p < 0.05). Also, Collector Filter group in station 6 is more abundant than other stations (p < 0.05). The results of the SIMPER analysis indicated a high degree of uniformity and reduction of variations at each station group seasonally.

In general, the results of this study showed that the stations that were located after the fish farms in many seasons, alternately collector filter and collector gatherer feeding groups most frequent. However, based on the results of the SIMPER test, due to the increased presence of other feeding groups in stations after fish farms, the contribution of the filterer and gatherer groups to the combination of macroinvertebrates in comparison with other stations decreased.