Stress responses of starry flounder, Platichthys stellatus (Pallas) following water temperature rise

Abstract

Stress responses of starry flounder, Platichthys stellatus (Pallas) following water temperature rise were investigated to establish the influence of ambient temperature on this species. The physiological indicators of stress were plasma cortisol, glucose, aspartate aminotransferase, alanine aminotransferase, sodium, chloride, osmolality and triiodothyronine (T3). No significant difference in plasma parameters were observed among the experimental groups of 15 degrees C, 18 degrees C and 21 degrees C. Level of plasma cortisol (49.0-95.0 ng ml(-1)) and glucose (56.1-58.1 mg dl(-1)) of starry flounders kept at 24 degrees C-27 degrees C were significantly higher than those (cortisol: 20.4-23.6 ng ml(-1), glucose: 40.6-47.1 mg dl(-1)) observed in the 15 degrees C-21 degrees C groups. Changes in aspartate aminotransferase and alanine aminotransferase following water temperature rise showed a similar pattern to plasma cortisol and glucose. Starry flounders exposed to 27 degrees C exhibited higher plasma sodium (164.7 mmol l(-1)), chloride (147.6 mmol l(-1)), and osmolality (450.7 mOsm kg(-1)) than those (sodium: 154.0-158.7 mmol l(-1), chloride: 139.1-140.4 mmol l(-1), osmolality: 375.1-383.8 mOsm kg(-1)) fish exposed to 15-21 degrees C. Though plasma T3 (29.4 ng ml(-1)) of starry flounder increased at 24 degrees C, this hormone was significantly lower (19.3 ng ml(-1)) in fish kept at 27 degrees C than those (24.6 ng ml(-1)) the fish at 15 degrees C. This phenomenon seems to be directly associated with long-term fasting. Accordingly, the results suggested that starry flounders got stressed with osmoregulatory disturbances above 24 degrees C.