Summary
Current interpretation of histological alteration in fish as an indicator of contaminant impact is subjective. Generally severity of alteration is poorly described, and does not allow direct comparison between studies. A histological health index (HHI) modified from Bernet et al (1999), uses various reaction patterns and a number of potential alterations, each with an importance factor based on its pathological importance to the fish. Each alteration is also given a score to indicate its severity. In the present study, we build on this and developed specific quantification of each alteration to define the severity score. Antarctic Rock-cod (Trematomus bernacchii) were collected at 6 sites from Prydz Bay near Davis Station, East Antarctica, during the 2012/13 summer. Twenty fish were collected at each of four sites along a spatial gradient starting at the sewage outfall (sites ranged from 0 up to 9 km south of the discharge point, in the direction of the predominant current) and from two reference sites (approximately 9 and 16 km north of the discharge point). All fish within close proximity to the outfall exhibited significant histological alteration in both gill and liver tissue. Common pathologies observed in fish closest to the outfall include epithelial proliferation and secondary lamellar fusion in the gills, and multifocal granulomatous response in liver tissue. The prevalence and severity of histopathology decreased with increasing distance from the outfall. Nitrogen stable isotope analysis supported this trend with higher assimilation of sewage derived nitrogen within the tissues of fish closest to the sewage outfall. Findings in the present study provide direct evidence of the impact of sewage on Antarctic biota, and highlight the value of incorporation of histopathological investigations as part of Antarctic-based EIA programs. The Health Index developed for T. bernacchii will allow for direct comparison of impacts to this fish in future studies.