Cortisol and thyroid hormone responses to acid stress in the brown trout, Salmo trutta L.

Abstract

Individual cannulated brown trout monitored during exposure to acidic water showed increased plasma cortisol after 3 h at pH 4.0 with low (0.05 mm) or high (2.8 mm) calcium (Ca) content, and after 2 days in acidic water with a high Ca content. Most fish did not survive for 2 days in acidic water with a low Ca content. Non‐cannulated fish showed a similar increase in mean plasma cortisol after 2 days in high‐Ca acidic water (pH 4.0–4.6), but not in acidic water of a low Ca content. After 7 days of exposure to acidic water, plasma cortisol appeared to recover when there was a high Ca content but increased 20‐fold when Ca content was low. In cannulated fish severe acid stress resulted in a marked and rapid thyroid response. Plasma thyroxine (T4) was elevated after 3 h exposure to acidic water of both low and high Ca content and remained elevated for 2 days of acid exposure with high Ca. In non‐cannulated fish an increase in mean T4 was apparent only after 7 days in low‐Ca acidic water. Plasma triiodothyronine (T3) levels were not significantly altered by any of the acid regimes. Plasma glucose of cannulated fish was elevated within 3 h of acid‐exposure and remained elevated after 2 days in high‐Ca acidic water.