Decomposition of Rainbow Trout (Oncorhynchus mykiss) Carcasses in a Forest Stream Ecosystem Inhabited only by Nonanadromous Fish Populations

The overall dynamics of rainbow trout (Oncorhynchus mykiss) carcass decomposition in a woodland stream ecosystem was examined in two experiments conducted in the West Fork of Mink Creek, Idaho: one during winter–spring (mean water temperature 4.2 °C) and one during summer (mean water temperature 8.6 °C). Relative weight loss (%AFDW) from fish during both periods was essentially constant. In spring, mean daily loss per day was 1.5%. Although this rate is comparable with the decay of high-quality ("fast") leaves, it took much longer than expected (> 120 d) for the even higher quality fish protein. In summer, decay was more rapid (4.9%/d) and was completed in less than half the time (~50 d). Most decay appeared to progress from inside the carcasses outward to the skin. The skin remained intact throughout most of both experiments. Nutrients leached from the fish appeared to be utilized rapidly by microbes associated with the carcass, since no stimulation of algal growth occurred immediately downstream of the carcasses. This suggests extremely tight nutrient spirals and high nutrient retention in Mink Creek and other comparable Rocky Mountain headwater streams.