The effects of environmental contaminants on the immune functions of marine flatfish

Given the widespread concern that chemical contaminants may be associated with infectious disease outbreaks in marine fish populations, work has been undertaken with the aim of developing a suite of non-specific and specific assays of marine fish immune function and the application of these techniques in a variety of field and laboratory investigations. Most of the work focused on dab, Limanda limanda (L.) in view of the importance of this species in several North Sea fish disease monitoring programmes, and was also supplemented with investigations of specific immune function in turbot, Scopthalmus maximus (L.). Initial field studies examined non-specific immune function in terms of lymphoid organ morphology in dab sampled along a North Sea gradient of chemical contamination during the March 1990 ICES/IOC Bremerhaven workshop. Significant differences were observed in the kidney and spleen cell populations from dab, and these observations were considered in view of the various other physico-chemical and biological results generated during the Bremerhaven workshop. Following the valuable experience gained of the practical aspects of the field monitoring approach, laboratory investigations were initiated with the aim of developing a suite of immune function assays for deployment in either laboratory or field studies of marine fish health. Assays for non-specific immune functions were considered, including serum protein and lysozyme levels, methods of phagocyte collection, phagocyte chemiluminescence, calorimetric detection of individual reactive oxygen species and in vitro cell migration assays. Additional field work was undertaken, with the monitoring of serum total protein levels and lysozyme activity in dab sampled from Lyme Bay, UK This study provided evidence of a marked seasonal variation in non-specific immune function, which appeared to be associated with environmental factors (e.g. water temperature) and the reproductive cycle. Selected non-specific assays were applied to dab and turbot exposed under controlled laboratory conditions to a variety of important marine contaminants, including cadmium, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), and the biological data integrated with appropriate chemical characterisation of the exposure matrix. Using cultured turbot as a test species, the non-specific assays were also supplemented with the assay of specific immune function in fish exposed to PCB contaminated sediments. In brief, there was evidence of significant impairment of immune function in fish exposed to either individual contaminants (viz. cadmium and PAHs) or contaminant mixtures (viz. PAHs and PCBs) under the laboratory conditions described. In summary, the project was successful in its primary aims of developing a suite of techniques for evaluating both cellular and humoral immune functions in marine flatfish, and applying these techniques in the laboratory to assess the impact of important classes of environmental contaminants on fish health. Selected techniques were also used in field monitoring studies of marine fish immune function, illustrating the potential of such techniques for use in future laboratory and field studies of fish health.