Effects of treated sewage effluent on immune function in rainbow trout (Oncorhynchus mykiss)

Abstract

In this study, the immune reactions of rainbow trout (Oncorhynchus mykiss) were examined, after exposure to 10, 30 and 70% of tertiary-treated municipal sewage effluent for 27 days. Exposures were conducted concurrently with and without an immune challenge using intraperitoneal injections of inactivated Aeromonas salmonicida salmonicida. Due to the time required to prepare and analyse samples, fish sampling was conducted over two consecutive days. There was no trout mortality for any of the experimental treatments. The exposure to effluent increased in vitro lymphocyte proliferation, decreased circulating lymphocytes and increased degrading erythrocytes in peripheral blood samples. Circulating lymphocytes were only decreased in the sham-injected, but not in the A. salmonicida-injected group. In addition to effluent effects, circulating lymphocytes and lymphocyte proliferation were decreased on day 2 of sampling as compared to day 1. Concentration-dependent degradation of erythrocytes was only observed on day 2 of sampling. Capture and removal of trout on day 1 of sampling presumably caused low-level stress that affected some results on day 2. Oxidative burst, phagocytosis, lysozyme, leucocyte populations other than lymphocytes and A. salmonicida-specific IgM production were not affected by exposure to effluent, and of these parameters, only oxidative burst and total leucocytes showed sampling day effects. From these results it can be observed, that with the exception of oxidative burst, those variables affected by effluent exposure were also significantly changed by the low-level sampling stress imposed by staggered sampling. Elevated liver mixed-function oxygenase activity as measured by 7-ethoxyresorufin-Odeethylase activity, and increased bile polycyclic aromatic hydrocarbon (PAH) metabolites were observed in response to sewage effluent exposure. As both PAHs and stress are known immune suppressors, it is difficult to conclude whether or not changes in immune parameters due to effluent exposure were caused by the direct action of chemicals, or were due to a general stress response.

Stimulation of reproductive growth in rainbow trout (Oncorhynchus mykiss) following exposure to treated sewage effluent

“…High coneentratiol1s up to 70% viv efflucnt caused fragility of red blood eell, elevated liver mono-oxygenases, and affected lymphocyte l1umbers and proliferation [33]. Immune endpoints examined in the same rainbow trout sampled in this paper showed a constant unspecific stimulation of different leucoeyte populations in immune organs reminiscent of chronic inflammation [34]. Decreases in serum lysozyme und circulating lymphocytes were also observed only in female trout from this experiment [32].…”

Sex and low-level sampling stress modify the impacts of sewage effluent on the rainbow trout (Oncorhynchus mykiss) immune system

“…Significantly reduced peripheral blood lymphocyte numbers were also observed in an earlier experiment with juvenile rainbow trout exposed to high concentrations of effluent from the same STP for 28 days (Hoeger et al, 2004b). Similarly, Kakuta (1997) reported lower lymphocyte numbers in goldfish (C. auratus) after exposure to treated effluent in a laboratory experiment.…”

“…A possible cause for the decrease of lymphocyte numbers could be polyaromatic hydrocarbons (PAH), as has been described before by Khan (2003), who found lower circulating lymphocyte numbers in winter flounder (Pleuronectes americanus) sampled at a PAH-polluted boat wharf. The presence of PAHs in the effluent used for the study at hand has been suggested by analysis of bile samples of trout exposed to higher concentrations of effluent from the same STP for 28 days (Hoeger et al, 2004b). As PAHs are known to be strong activators of cytochrome P450 1A1, the significant induction of liver EROD activity in effluentexposed trout, whether as juveniles for 28 days (Hoeger et al, 2004b) or as adult male fish for 32 weeks (this study), further supports the assumption that these fish were exposed to PAH via the sewage treatment effluent used.…”

“…The presence of PAHs in the effluent used for the study at hand has been suggested by analysis of bile samples of trout exposed to higher concentrations of effluent from the same STP for 28 days (Hoeger et al, 2004b). As PAHs are known to be strong activators of cytochrome P450 1A1, the significant induction of liver EROD activity in effluentexposed trout, whether as juveniles for 28 days (Hoeger et al, 2004b) or as adult male fish for 32 weeks (this study), further supports the assumption that these fish were exposed to PAH via the sewage treatment effluent used. At first sight it seems contradictory to explain the reduced lymphocyte numbers observed in female trout by exposure to PAHs while an increase in EROD activity was not demonstrated in mature females in the present study.…”

Immune deficiency causes annual late summer brown trout (Salmo trutta) mortality in Austrian prealpine river systems

“…Stress and immune functions are linked in all vertebrates, including teleost fish, and persisting stress can act immunosuppressive (Puangkaew et al 2004). Environmental pollutants such as, e.g., polychlorinated biphenyls (PCBs) (Ouabius et al 2005) or municipal sewage effluent (Hoeger et al 2004) are immunotoxic and impair the ability of fish to respond to additional stressors (Köllner et al 2002). Prolonged changes in natural photoperiod (Leonardi and Klempau 2003), diet, temperature (Bly and Clem 1992;Le Morvan et al 1998), artificial or natural solar UV radiation (Markkula et al 2005a(Markkula et al , 2005bSalo et al 2000), and bacterial or viral diseases affect the immune system of teleost fish and Salmonidae in particular.…”