Immune parameters of plaice, Pleuronectes platessa, L. along a sewage sludge gradient in the Firth of Clyde, Scotland

Plaice were caught at five stations varying in distance from the sewage sludge dumping site at Garroch Head, in the Firth of Clyde, Scotland and a number of physical and immunological parameters monitored. Significant intergroup differences were apparent in condition factor, hepatosomatic index, serum protein concentration, serum lysozyme, serum immunoglobulin (Ig), liver vitamin E, kidney leucocyte respiratory burst activity and kidney leucocyte bactericidal activity. Of these parameters, the hepatosomatic index, serum lysozyme, serum Ig and kidney leucocyte bactericidal activity showed a negative correlation with distance from the dump site (that is, were highest at the dump site); serum protein and liver vitamin E showed a positive correlation. Factors found not to vary between the groups included the spleen index, serum antiprotease activity and kidney leucocyte phagocytic activity. These findings are discussed in relation to recent experimental data on the effects of sewage sludge exposure on the immune system of fish.