Reproductive and histopathological effects of long-term experimental exposure to bis(tributyltin)oxide (TBTO) on the three-spined stickleback, Gasterosteus aculeatus Linnaeus

Three-spined sticklebacks, Gasterosteus aculeatus Linnaeus, were exposed to 0, 0.1, 1.0, 2.5 and 10 μg bis(tributyltin)oxide (TBTO) 1⁻¹ for up to 7.5 months in a flow-through system of sea water. As early as 4 weeks after the start of the experiment, fish from the 10 μg TBTO 1⁻¹ group showed diminishing appetite, increasing lethargy and opaque eyes. The mortality in this group after 2 months of exposure was 80%. No significant differences between the control and the exposed groups were noted concerning fecundity, hatched fry and frequencies of malformed fry. The gonad somatic index (GSI) was determined before and during the spawning period. GSI in control fish increased significantly, while that in the exposed groups remained unchanged between the two sampling occasions. Structural examination of the gills from fish exposed for 2 months to 10 μg TBTO I⁻¹ revealed fusion between secondary lamellae and gradual cell degeneration. The chloride cells were characterized by degenerating mitochondria. Hepatocytes in fish exposed to 2.5 and 10 μg TBTO I⁻¹ contained an increased number of lipid-containing vacuoles and the nucleoli were disorganized and fragmented.