Endocrine, osmoregulatory, respiratory and haematological parameters in flounder exposed to the water soluble fraction of crude oil

Flounders Pleuronectes flesus with an implanted vascular catheter were exposed to a 50% dilution of the water soluble fraction (WSF) of Omani crude oil (c. 6ppm total aromatic hydrocarbons) and serial blood samples taken to determine their endocrine status (cortisol, catecholamines and thyroid hormones) and the resultant and/or causal physiological (haematological, ionoregulatory and respiratory) disturbances. This resulted in a progressive increase in plasma cortisol concentrations from 3 h onwards (rising from 18 to 51 ng ml−1 after 48‐h exposure), and increased plasma glucose concentrations indicating a generalized stress response. Plasma T3 and T4 concentrations of both control and WSF‐exposed groups declined progressively over the experimental period; exposure to the WSF of crude oil further depressed plasma T4 concentrations but not plasma T3 concentrations relative to those of control fish. Plasma osmolality and sodium and chloride concentrations were stable in WSF‐exposed fish, however, plasma potassium concentrations were increased significantly at the 24‐and 48‐h sampling points. The most profound physiological disturbance in WSF‐exposed fish was a dramatic decline in blood oxygen content (CvO2) (from 2–8 to 0–8 ml 100 ml−1 after 48‐h exposure), which is likely to be the cause of the increased plasma noradrenaline concentrations from 3 h onwards. Increased noradrenaline is likely in turn to have been responsible for the significant increase in blood haematocrit and blood haemoglobin at the 3‐h sampling point, although the dominant effect in the longer‐term was a significant decline in both of these haematological parameters.