Assimilation of freshwater salmonid aquaculture waste by native aquatic biota

An experimental finfish aquaculture farm was operated in a small lake at the Experimental Lakes Area in northwestern Ontario, Canada. In this Study, we used the distinct and enriched carbon and nitrogen isotope ratios (delta(13)C and delta(15)N) of rainbow trout (Oncorhynchus mykiss) feed and waste to determine whether the operation provided a novel source of energy for native biota. For 1 year prior to and for 3 years during the cage culture, we collected littoral, pelagic, and profundal invertebrates and minnows from the experimental and reference lakes. In both the second and third years of aquaculture, there was a significant increase in delta(15)N of all organisms sampled in the experimental lake; mean delta(15)N values of littoral, pelagic, and profundal invertebrates and minnows shifted towards the signature of the fish feed by up to 4.2 parts per thousand. Significant increases in delta(13)C of up to 2.6 parts per thousand were observed in Mysis, profundal chironomids, and minnows but not in littoral invertebrates or zooplankton. Aquaculture waste became a progressively more important component of minnow diets over the course of this study. The dissolved and (or) particulate wastes of the cage operation became a novel source of energy for the native biota in this experimental lake.