Physiological status of whitefish (Coregonus lavaretus pallasi) prior to spawning in lakes of differing acidity

Abstract

One-summer-old whitefish were released into three small lakes: a circumneutral lake (mean water pH 6.09, Ca2+ 0.06 mmol l–1 and total aluminium 11 mg l–1) and a moderately acidic lake (pH 5.17, Ca2+ 0.05 mmol l–1 and Altot 36 mg l–1), both with abundant perch and earlier introduced whitefish, and a highly acidified lake (pH 4.53, Ca2+ 0.03 mmol l–1 and Altot 145 mg l–1) with a sparse perch population. Three years later, when the released whitefish were expected to become sexually mature, whitefish were sampled from the lakes near the spawning time to evaluate their reproductive and physiological status. In the circumneutral lake, 72% of the captured whitefish were mature, while in the moderately acidic lake all seven captured fish were immature. Among the 27 captured whitefish in the highly acidified lake, all except one were mature. However, the ovaries of two of the 11 females (18%) contained a high proportion of atretic oocytes, and only 54% of the males had running milt compared with 94% in the circumneutral lake. This deterioration of gonadal maturation had probably resulted from physiological stress caused by the high Al and low Ca2+ concentration in the acidic water, which also appeared as a disturbed ion balance, an increased blood glucose and haemoconcentration, and a low length increment in relation to the weight increase. Apart from the imbalance in the length and weight increase, the results of the present study are consistent with those from laboratory experiments. By interfering with whitefish physiology, the acidification of freshwater lakes may also impair their reproduction.