pH - Update

A study [ Long-term effects of water pH changes on hematological parameters in the common carp (Cyprinus carpio L.), Mahdi Ghanbari1* and Mansoureh Jami2] was conducted  for the purpose described in the study abstract below.

 “The aim of this study was to examine the effects of water pH changes on certain hematological parameters of fingerlings of common carp (Cyprinus carpio), in water with different pH (acidic and alkaline). Fingerlings of common carp were subjected to acidic (pH 5.5 and 6.5) and alkaline (pH 8.0, 8.5 and 9.0) water for 21 days. Control groups were maintained at neutral pH. The result showed that exposure to both acidic and alkaline water exerted stress on fish and considerably affected the hematology of fingerlings of common carp. Cytological study revealed that such swollen erythrocytes with centrally located swollen nucleus and also immature erythrocytes were observed in fingerlings exposed to pH 8.5 - 9.0. Exposure to the two extreme pHs (pH 5.5 and 9.0) caused significant reductions (P < 0.05) in total erythrocyte count (TEC) in common carp. A significant reduction (P < 0.05) in the hemoglobin content was observed at the two extreme pHs 5.5 and 9.0. The total leukocyte count (TLC) was reduced at pH 5.5, but only after a brief increase at pH 6.5. Alkaline range also experienced a reduction in TLCs at pH 8.0 and underwent further reduction with increased pH. Blood glucose was significantly higher (P < 0.05) in fingerlings exposed to both acidic and alkaline waters and the increase was proportional to the degree of pH change. Serum protein levels were also significantly reduced (P < 0.05) following exposure of the fingerlings to both acidic and alkaline conditions. The changes in hematological parameters of the fingerlings of common carp indicated that the change in water pH might have caused the ion regulatory and acid–base disturbances originating at the gill leading to the altered internal pH, electrolyte and osmotic balances that imply an increase in energy consumption to restore homeostasis instead of other physiological functions, weight gain and growth.”

This study further substantiated previous widely held beliefs concerning the effects of extreme values of pH (5.5 and 8.5 – 9.0) on Cyprinus carpio (Koi) by defining the physiological changes that occur within the blood chemistry at acidic and alkaline extremes in pH values. Red and white blood cell levels and production were noticeably negatively affected; hemoglobin levels were also severely affected, as were glucose and serum protein levels. The possibility of respiratory stress was indicated by the reduction of hemoglobin in both acidic and alkaline conditions.

Although the pH range of 6.5 – 8.5 remains widely accepted for homeostasis, this study also indicates that certain levels of stress are experienced as the limits of this range are approached and chronic exposures to these range limits could result in extended physiological impairments.

This is not to say that brief exposures to these pH extremes are harmful. They are experienced by all fish in the diel rhythms that occur in aquatic eco-systems. When these levels become problematic is when the average maintained pH level is near these extremes.