Effects of Short- and Long-term Ultraviolet B Irradiation on the Immune System of the Common Carp (Cyprinus carpio)¶

Abstract

Carp (Cyprinus carpio) were repeatedly exposed to 0, 60, 120 and 240 mJ/cm2 ultraviolet B (UVB) radiation three times in 1 week (short-term exposure) or 12 times in 4 weeks (long-term exposure). The effect of UVB on the functioning of the carp immune system was studied on day 2 after the final irradiation. After short-term UVB exposure, the whole-blood respiratory burst and cytotoxic activity were markedly enhanced, with parallel responses in both the number of circulating granulocytes and in the plasma cortisol concentration of the fish. These changes were not detectable after long-term exposure. The respiratory burst by head kidney granulocytes was suppressed dose dependently after both exposures, but cytotoxic activity was not affected. Exposure to UVB also modulated lymphocyte functions: nonstimulated and PHA-stimulated proliferation of head kidney lymphocytes in vitro was enhanced by both short-term and long-term exposure. LPS-stimulated proliferation was not affected by exposure nor was the number of immunoglobulin-secreting cells in the head kidney. In long-term exposure, the highest dose reduced the level of plasma IgM. This study indicates that UVB irradiation induces immunomodulation in the blood and head kidney of the carp and that the effects of short- and long-term exposure differ from each other. The results emphasize the potentially harmful impact of increased solar UVB radiation on fish immune functions.

Adverse Effects of Ultraviolet Radiation on Growth, Behavior, Skin Condition, Physiology, and Immune Function in Gilthead Seabream (Sparus aurata)

“…In this study, after short-term exposure, UVB-L exposed fish (2.4 kJ m −2 d −1 ; absolute UVB doses after 10 days of exposure -24.0 kJ m −2 ) showed the highest plasma cortisol levels. Similar findings were observed in common carp (0.6 kJ m −2 d −1 , absolute UVB doses after a total of 3 irradiations -1.8 kJ m −2 ; Markkula et al, 2005) and rainbow trout (0.07 kJ m −2 d −1 , absolute UVB doses after a total of 17 irradiations -1.2 kJ m −2 ; Markkula et al, 2009) juveniles exposed to UVB. Fish exposed to the lowest UVB doses unexpectedly had the highest increase in cortisol levels.…”

“…After 43 days of exposure, there were no significant changes in the cortisol levels between control and any of the UVB-exposed fish, probably due to adaptation to these chronic stress conditions, which can result in its reduction to basal levels (Alves et al, 2010). Similar results were obtained in common carp (absolute UVB dose, 28.8 kJ m −2 ) and rainbow trout (absolute dose, 10.2 kJ m −2 ) after long-term exposure (Markkula et al, 2005(Markkula et al, , 2009. Low hematocrit values and a decrease in the plasma total protein levels have been used as indicators of poor nutritional status due to UVA and UVB exposure (Jokinen et al, 2000(Jokinen et al, , 2008(Jokinen et al, , 2011Markkula et al, 2005Markkula et al, , 2009.…”

“…Indeed, under acute exposure to UVR, cortisol levels in plasma increased significantly in roach and fathead minnow (Jokinen et al, 2000;Manek et al, 2012). The cortisol peak in the juveniles from the UVB-H and UVB-M treatments due to UVB exposure probably occurred before the 10th day of exposure, as suggested also in Markkula et al (2005Markkula et al ( , 2009. After 43 days of exposure, there were no significant changes in the cortisol levels between control and any of the UVB-exposed fish, probably due to adaptation to these chronic stress conditions, which can result in its reduction to basal levels (Alves et al, 2010).…”

“…Similarly, in our experiment, observed skin lesions were located in the same body region. Additionally, UVB exposure (2.4 kJ m −2 d −1 ; absolute UVB doses after 28 days, a total of 12 irradiations -28.8 kJ m −2 ) induced morphological changes in the skin of common carp (Markkula et al, 2005). Moreover, more than 50% of fish showed lesions and sunburn on their skin after 28 days of exposure (Markkula et al, 2005).…”

“…UVB-induced immunomodulation has been demonstrated in peripheral blood, spleen and head kidney (Salo et al, 1998;Jokinen et al, 2000;Markkula et al, 2009). The occurrence of lymphopenia and granulocytosis in peripheral blood is considered a stress indicator of UVB exposure in roach, common carp, rainbow trout, and three-spined stickleback, even after long-term exposure (Salo et al, 1998;Jokinen et al, 2000;Markkula et al, 2005Markkula et al, , 2007Vitt et al, 2017). Moreover, in Atlantic salmon, long-term exposure to UVB resulted in a decrease of both immunoglobulin M (IgM) levels and complement bacteriolytic activity in the plasma (Jokinen et al, 2008(Jokinen et al, , 2011.…”