Toxic substances and reproductive disorders in Baltic fish and crustaceans

In the Baltic Sea ecosystem reproductive disorders have occurred in top con sumers such as seals and some fish-eating birds, due to biomagnification of toxic substances, e.g. DDT and PCBs. Reproductive disturbances have also a ffected fish during the last 25 years. However, there is no strong evidence that toxic substances have caused these problems. Rather, the disorders se em to result from a combination of two or more biotic or abiotic factors. T he M74 syndrome, which kills fry of salmon and sea trout, is characterized by a deficiency of thiamine (vitamin B-1). Several factors may contribute t o the thiamine deficiency including the diet of salmon in the sea and halog enate organic compounds. Cod do not develop M74, and poor cod recruitment i s mainly due to poor oxygen conditions in the spawning areas in combination with overfishing. Toxic compounds in pulp-mill effluents retard gonadal de velopment in perch, but the mechanisms and the active substances have not b een identified. Recruitment problems in perch in the coastal waters outside some pulp mills may also be explained by a lack of food items for juvenile fish, rather than reproductive failure. There are very limited data on rep roductive disorders in crustaceans from the Baltic Sea. Most data come from studies of the benthic amphipod Monoporeia affinis, which has been used in monitoring programs. Several signs of reproductive disorder have been repo rted in this amphipod, e.g. malformation and death of embryos, and asynchro nous maturation of males and females.