Impact of UV-B radiation on the digestive enzymes and immune system of larvae of Indian major carp Catla catla JAIGOPAL SHARMA, Y. VASUDEVA RAO, S. KUMAR & RINA CHAKRABARTI Aqua Research Lab, Department of Zoology, University of Delhi, Delhi, India (Received 5 June 2009; Revised 3 August 2009; Accepted 9 September 2009) Abstract Purpose: Ultraviolet radiation is a potent threat to the aquatic animals. Exposure to such stressor affects metabolic and immunological processes. The present investigation aims to study the effect of UV-B radiation on digestive enzymes and immunity of larvae of Catla catla. Materials and methods: Larvae were exposed to ultraviolet-B (UV-B, 280–320 nm) radiation (145 mW/cm 2 ) for three different exposure times of 5, 10 and 15 min on every other day. After 55 days, important digestive enzymes were assayed. For immunological study, lysozyme, glutamate oxaloacetate transaminase (GOT) and glutamate pyruvate transaminase (GPT) levels were measured. Then the fish were kept for one month without radiation and lysozyme level was measured. Results: Protein concentration varied directly with the duration of exposure and was highest among fish that had received the 15 min UV-B irradiation. Significantly higher amylase, protease, trypsin and chymotrypsin activities were found in 5 min exposed fish compared to others. Lysozyme level was significantly higher in control group compared to the UV-B treated fish. The lysozyme level decreased with the increasing duration of UV-B radiation. When fish were kept without UV-B radiation for one month, lysozyme level was brought to the normal level in all treatments, except 15 min exposed fish. The GOT and GPT levels were significantly higher in the 15 min exposed group than others. Conclusions: The effects of UV-B radiation on the digestive physiology and immune system of catla have been clearly observed in the present study. The decreased enzyme activities in UV-B radiated fish results into improper digestion and poor growth. Keywords: Catla catla, UV-B irradiation, digestive enzyme, immune system Introduction Ultraviolet-B radiation (UV-B), a component of solar radiation, is a potential threat to aquatic life. The detrimental effects of UV-B (280–320 nm) on aqua- tic ecosystems have been well documented (Hader et al. 1998). Ceriodaphnia dubia exposed to dissolved- phase weathered oil in the presence of environmen- tally realistic solar radiation, exhibit 1.3–2.5 times greater sensitivity, relative to organisms exposed under traditional laboratory fluorescent light (Calfee et al. 1999). Exposure to harmful levels of ultraviolet- B radiation has been suggested as major cause of amphibian declines (Little et al. 2003). Studies on the impact of UV-B radiation in the aquatic system, especially on the animal of higher trophic level like fish, is economically important. Exposure of plank- tonic fish eggs and larvae to UV-B results in higher mortality that may lead to poorer recruitment to the adult populations of marine and freshwater fishes (Williamson et al. 1997, Walters and Ward 1998). UV-B exposure impairs the immunological resistance to infectious disease in rats and human; it increases susceptibility to viral, fungal and bacterial infections, as well as to parasitic diseases and antigenic tumours (Jokinen et al. 2000). In fishes, UV-B radiation can induce injury to the skin, including sunburn, and appearance of sunburn cells, epidermal hyperplasia, depletion of the mucus layer, solar elastosis with wrinkling, melanomata (Bullock 1988, Berghahn et al. 1993, Little and Fabacher 1994, Blazer et al. 1997, Miguel et al. 2003, Sharma et al. 2005). UV-B radiation has severe effects on early life stages of fishes such as lesions in the brain and retina, and reduced growth rate (Hunter et al. 1979). UV-B radiation severely damaged gills of Catla catla, the primary Correspondence: Prof. Rina Chakrabarti, PhD, Aqua Research Lab, Department of Zoology, University of Delhi, Delhi - 110 007, India. Tel: þ91 11 27666496. E-mail: aquaresearchlab@yahoo.co.in Int. J. Radiat. Biol., Vol. 86, No. 3, March 2010, pp. 181–186 ISSN 0955-3002 print/ISSN 1362-3095 online Ó 2010 Informa UK Ltd. DOI: 10.3109/09553000903419312