Effects of cumulative stress on fish health near freshwater outlet sluices into the sea: a case study (1988-2005) with evidence for a contributing role of chemical contaminants.

Epizootic skin diseases in euryhaline flounder (Platichthys flesus) in the Dutch Wadden Sea were first reported in 1988. Particularly high prevalences of skin ulcers (up to one-third of individual fish being affected) were encountered in the vicinity of sluices draining freshwater from IJsselmeer Lake, in contrast with much lower levels in the freshwater bodies behind the sluices and open sea areas (<2%). It was proposed that salinity stress, high bacterial loads, nutritional deficiencies, and obstruction to fish migration by the sluices could all be involved in disease causation. Results of follow-up surveys at these outlet sluices from 1994 to 2005 further substantiate our preliminary findings. The follow-up data also show a general reduction in disease and improved condition factor during this period, which can be explained by improved habitat conditions for the flounder, partly due to effective sluice gate management. Furthermore, statistical correlations (p<0.05) were demonstrated between flounder ulcer occurrence and chemical contaminant concentrations in liver (Hg, Cd, Cu, Zn) and bile (the metabolite 1-OH pyrene as an indicator of chronic polycyclic aromatic hydrocarbon exposure), and histological liver lesions generally indicative of contaminant exposure (hydropic vacuolization of biliary duct epithelial cells). The findings suggest that a combination of osmotic and contaminant-induced stress also contributed to the observed disease patterns.

Long-term trends in the prevalence of cancer and other major diseases among flatfish in the southeastern North Sea as indicators of changing ecosystem health.

This paper analyses and discusses spatial and temporal patterns in the prevalence of major skin diseases (lymphocystis, epidermal hyperplasia/papilloma, ulcers), intestinal parasite Glugea sp., and liver cancer in dab (Limanda limanda) and flounder (Platichthys flesus) in the Dutch section of the North Sea since the mid-1980s. We have attempted to relate disease prevalence trends in both species to chemical contaminant exposure and other relevant environmental factors including fish condition factor, population density, fishing activity, and water temperature. We observed a long-term decline in chemical-related liver cancer in the populations of both species since the early 1990s. Lymphocystis and skin ulcer (flounder only) have also displayed a significant decrease since then. We conclude that the widespread decline in the prevalence of several skin diseases and liver cancer in dab and flounder in Dutch waters in the past two decades is most likely due to the improved water quality and health conditions in this region.

Growth of Corophium volutator under laboratory conditions.

Temperature-dependent growth is an important factor in the population model of Corophium volutator that was developed to translate responses in a 10-day acute bioassay to ecological consequences for the population. The growth rate, however, was estimated from old data, based on a Swedish population. Therefore, new growth rates are estimated herein from two experiments using Corophium volutator. To save time, a tool was developed to use image analysis to measure Corophium volutator. The experiments show that Corophium volutator has a low growth rate at low temperatures (5-10 degrees C). At higher temperatures no difference in growth rate between 15 degrees C and 25 degrees C was found. The growth rate from these experiments is comparable to data found in literature. A new relationship between temperature and individual growth was estimated, and incorporated into the Corophium population model. As the model also uses the same temperature relationship for reproduction, the modelled population growth rate at different temperatures changes as a result of the new data. The new growth rate and the updated temperature relationship result in reduced tolerance to external stressors, as previously predicted by the model.

A chronic bioassay with the estuarine amphipod Corophium volutator: test method description and confounding factors.

Methods of conducting a chronic sediment toxicity test with the estuarine amphipod Corophium volutator are described. They consist of a 49-day exposure, after which mortality, growth and reproduction are determined. Pilot experiments were used to optimize test design parameters such as temperature, duration, feeding and refreshing regimes, and effects of indigenous organisms. By way of further validation, the present study focused on the effects of four different parameters: oxygen saturation, salinity, ammonium and nitrite. These confounding factors might play an important role especially if the test is used for risk assessment of field-contaminated sediments. It is concluded that the present experimental design is well suited for chronic sediment exposures with C. volutator. The test can be performed at a broad range of salinity values, provided that controls are performed at the same salinity. Results further demonstrate that with the endpoints growth and reproduction this chronic test procedure is a factor 7-18 more sensitive to ammonium and nitrate than the standardized acute bioassay (endpoint mortality).