Histopathology Biomarkers as Tools to Characterize the Health Status of Delta Smelt

The health of wild populations of fish is a result of a series of complex interactions with numerous variables in the aquatic environment. The presence of toxic- and infectious- diseases is viewed as the ultimate health indicator because it represents the cumulative effects of multiple stressors, many of which may be unknown or poorly defined. Histopathology biomarkers were investigated as an initial weight-of-evidence approach to assess health status on juvenile and adult delta smelt (Hypomesus transpacificus) in the upper San Francisco Estuary. The tissue damage of the organs was assessed semi-quantitatively based on ranking severity of lesions. There was no evidence of significant bacterial or parasitic infestations in juvenile or adult smelt. Juvenile smelt collected from Suisun Bay had a greater variety, higher prevalence, and more severe gill and liver lesions. Adult smelt collected from Suisun Bay, Suisun Marsh, south Delta and north Delta had higher liver lesions when compared to those from the central Delta. Intersex in testis, preneoplastic lesion in liver, and papilloma in gill of smelt suggested prior exposure to contaminants including endocrine disrupting chemicals. Our results suggest that restoration efforts should focus on Suisun Bay, Suisun Marsh, north Delta, and south Delta for contaminant effect on smelt. A high management priority should be to continuously monitor and protect of delta smelts and the habitats where they thrive to help support and restore their populations.