Friedrich M., Stepanowska K., 1998. Impact of high cortisol level-observed in the blood of two-year-old carp (Cyprinus carpio L.) and caused by different colour of their aquaria-on the electrolyte content and osmolarity. Acta Ichthyol. Piscat. 28 (1): 75-80.

It was determined in the present study that a 14-day stay of carp in blue, yellow, and red aquaria caused significant increase of cortisol levels compared to its initial state and to that of fish kept in aquaria of a natural colour. This in turn caused a decrease in the levels of sodium and chloride ions and statistically significant decrease in potassium ion content.