Histopathologic biomarkers in three spined sticklebacks, Gasterosteus aculeatus, from several rivers in Southern England that meet the freshwater fisheries directive.

This study demonstrates the utility and sensitivity of histopathologic biomarkers by recording lesions to the gill, liver and spleen in three spined sticklebacks (Gasterosteus aculeatus) from several rivers in Southern England which broadly comply with the water quality directives to protect fish health. The main study site was the Letcombe Brook system near Wantage, graded 1 (good) to 3 (fair) by the Environment Agency, using the River Ecosystem (RE) Class system. Sites with similar grades on the rivers Erme, Clyst, Exe and Plym were also selected in Devon. A normal condition factor (0.9 +/- 0.02, mean +/- S.E., n = 90), the presence of food in the stomach, and the whole body ionic composition (Na, K, Mg, Ca, Cu, Zn) suggested that fish were generally healthy. All fish showed some minor incidence of gill and liver lesions, even in the best (grade RE1) river water quality. Scoring the percentage of branchial secondary lamellae showing lesions did not reflect water quality because of biotic factors such as parasite load. However, fatness of secondary lamellae (length/width) increased in lower class rivers. Hepatic fatty change and focal necrosis was related to river quality grades with fatty change increasing from 0.8% to 12% of total liver area in grade RE1 and RE2 rivers, respectively. The gross anatomy of the spleen showed normal red and white pulp, and sinusoid space varied between 11% and 34% of the tissue area, but was not correlated with river grade. Overall, we conclude that histopathologic lesions are present in fish even when water quality meets the Freshwater Fisheries Directive. The Directive therefore only partly protects fish health. The incidence of fatty change in the liver, or fatness of secondary lamellae, in adult three spined sticklebacks are suggested as simple but sensitive histopathologic biomarkers which may be used to protect freshwater fishes as a novel alternative approach to water quality based Directives. We propose histopathologic biomarkers of the three spined stickleback for routine monitoring of fish health in EU freshwaters.