Effects of Acid Water Exposure on Plasma Cortisol, Ion Balance, and Immune Functions in the “Cobalt” Variant of Rainbow Trout

Abstract

This study was undertaken to examine physiological responses to acidification of environmental water in the "cobalt" variant of rainbow trout (Oncorhynchus mykiss), which exhibits malformation of the pituitary, by following changes in plasma levels of cortisol and electrolytes, blood pH, gill Na(+), K(+)-ATPase activity, and immune functions after exposure to acid water (pH 4.5). Resting levels of plasma cortisol and lysozyme were significantly lower in the cobalt variant than in the normal trout, whereas plasma ceruloplasmin was significantly higher in the cobalt variant, suggesting that some endocrine factors, lacking or deficient in the cobalt variant, are important for the regulation of its immune functions. Blood pH was slightly but significantly lower in the cobalt variant at rest. After exposure to acid water for 24 h, both the normal trout and cobalt variant showed a significant elevation in plasma cortisol, although the increased level in the cobalt variant was still lower than that in the normal trout transferred to neutral water. No differences were seen in blood pH, plasma electrolytes, and gill Na(+), K(+)-ATPase activity between the normal trout and the cobalt variant, indicating that the cobalt variant regulates ion balance when exposed to acid water, despite malformation of the pituitary. Although the normal trout showed a reduction in plasma lysozyme level after acid exposure, there was no significant change in the cobalt trout. Adverse effects of pituitary malformation on ion balance and immune functions may be compensated by extrapituitary factors in the cobalt variant when it is exposed to acid water.

Modulation of the immune system of fish by their environment

“…A report on rainbow trout showed that reducing the pH to 4.5 resulted in a reduction in the levels of lysozyme in the plasma [73]. A study on Nile tilapia maintained animals at pH 7.9 and pH 4 for 2 weeks and found a highly significant (P < 0.001) increase in lysozyme levels at the lower pH after 2 weeks [34].…”

Cytokine Responses in Gills of Capoeta umbla as Biomarkers of Environmental Pollution

“…Freshwater does not have the same level of buffering and so can experience wide changes in pH (Camargo and Alonso, 2006;Monteith and Evans, 2005;Wright et al, 2005). A report on rainbow trout showed that reducing the pH to 4.5 resulted in a reduction in the levels of lysozyme in the plasma (Yada et al,. 2006).…”