Petz-Glechner, R., Patzner, R.A., Jagsch, A.

Effects of suspended solids from reservoir flushing on some tissues of rainbow trouts (Oncorhynchus mykiss): A qualitative study

Summary: The effects of increased concentrations of suspended sediments on rainbow trouts (Oncorhynchus mykiss) were studied in order to assess concentration and exposure time combinations, which do not lead to sustained damages. The experiments were conducted under standardized laboratory conditions in an aquarium in order to control environmental parameters. A special experimental apparatus was constructed for this. Water temperature and content of oxygen were kept constant. Two different kinds of sediments were tested. Concentrations of suspended sediments between 2.5 and 80 g/liter and exposure times between 1 and 48 h were used. These concentrations and exposure times are comparable to figures encountered during flushing of reservoirs in Austria. Immediately after the exposure to suspended solids, gills, epidermis and cornea were taken and investigated with the light- and scanning electron microscope. Unexposed fish were used as controls. Up to a concentration of 50 g/l neither epidermis nor cornea showed obvious damages. The epidermis was damaged by high concentrations (80 g/l, sometimes 50 g/l). Gills, however, were already affected by low concentrations and short exposure times. This effect is an enlargement of mucous cells. The mucus is apparently produced to protect gills from the tiny mineral particles. This enables the fish to endure low to moderate concentrations of sediments for several hours. Advices for flushing of reservoirs are discussed from a fish-ecological point of view.