ISSN 0032-9452, Journal of Ichthyology, 2010, Vol. 50, No. 5, pp. 396–401. © Pleiades Publishing, Ltd., 2010. Original Russian Text © V.V. Kuz’mina, B.A. Levin, Lyu Vei, P.V. Rusanova, 2010, published in Voprosy Ikhtiologii, 2010, Vol. 50, No. 3, pp. 405–410. 396 INTRODUCTION Thyroid hormones (TH) belong to major hor- mones functioning in fish since the earliest ontogene- sis. TH belong to the hypothalamo-pituitary-thyroid axis (Power et al., 2001; Blanton and Specker, 2007). They are important in many metabolic and morpho- genetic processes, in unfolding of metamorphosis, regulation of the reproductive system, and in regener- ation of particular organs (Pickford and Atz, 1957; Leatherland, 1982; Blanton and Specker, 2007; Sekimizu et al., 2007). TH participate also in hormo- nopoiesis of some hormones (Chernysheva, 1995). Recently, a great role of TH in the formation of the definitive state of phenotype in fish was revealed and the potential effect of the thyroids status on evolution- ary events via radical change of developmental param- eters was shown (Smirnov et al., 2006; Smirnov and Levin, 2007). It is supposed that thyroxin (Т 4 ) is a prohormone while 3,5,3'-triiodothyronine (Т 3 ) is a more active form of TH formed by the denonodenization of thy- roxin (Blanton and Specker, 2007). Some substances, so-called goitrogens, may block the synthetic activity of the thyroid gland and provoke the deficiency of TH in blood plasma (Brown, 1997). A considerable impact of the level of TH is rendered by the nutritive status. In particular, it was shown that the level of TH depends on the satiation level of fish. Brief starvation decreases concentration of Т 3 and Т 4 circulating in the blood of tench Tinca tinca supporting the relationship between the nutritive status and the function of the thyroid gland. Two days after the beginning of feeding fish, the level of hormones restores (de Pedro et al., 2003). As TH significantly influence the development rate of fish and the presence of food in the digestive tract influences the rate of their synthesis and their level in blood, it is interesting to simultaneously inves- tigate the effects of TH on the growth rate and on the activity of digestive enzymes in fish. The aim of the present study is the investigation of the effect of the active form of TH—Т 3 and goitrogen (thiourea) blocking the synthesizing activity of the thyroid gland on the rate of linear and weight growth and also the activity of proteinases and glycosidases of the intestinal mucosa, providing hydrolysis of protein and carbohydrate components of fish food (with refer- ence to roach Rutilus rutilus). MATERIAL AND METHODS The study was made during summer 2007–winter 2009. The principal object was juvenile roach; for comparison, juvenile sterlet Acipenser ruthenus was also investigated. The spawners of roach were caught in the Rybinsk Reservoir near Borok (Yaroslavskaya oblast). The eggs were fertilized on May 15, 2007, by Effect of Thyroid Hormones on Activity Dynamics of Enzymes of Intestinal Mucosa of Juvenile Roach Rutilus rutilus V. V. Kuz’mina a , B. A. Levin a, b , Lyu Vei c , and P. V. Rusanova a a Institute of Biology of Inland Waters, Russian Academy of Sciences (IBIW RAS), Borok, Nekouzskiy raion, Yaroslavl oblast, 152742 Russia e-mail: vkuzmina@ibiw.yaroslavl.ru b Institute of Ecology and Evolution, Russian Academy of Sciences, Leninskii pr. 33, Moscow, 119071 Russia c Neilunjiang Research Fisheries Institute, Harbin, China Received March 16, 2009 Abstract—The effect of thyroid hormones on activity dynamics of enzymes (proteinases and glycosidases) of intestinal mucosa of juvenile roach Rutilius rutilus was investigated. Application of substances increasing and decreasing the level of thyroid hormones in blood plasma significantly influences the growth rate and the activity of proteinases and glycosidases functioning in the intestinal mucosa. In most cases, the activity level of trypsin-like proteinases and the activity of glycosidases in the fish exposed to triiodothyronine were signif- icantly higher than in the control. The activity level of chymotrypsin-like proteinases in fish form the group with exposure of exogenous triiodothyronine only in the end of the experiment surpassed the values of this parameter in the control fish. In the fish developing at deficiency of thyroid hormones, the growth rate and proteinases activity were significantly lower in comparison with the control. DOI: 10.1134/S003294521005005X Key words: thyroid hormones, digestive enzymes, proteinases, glycosidases, intestine, dynamics of enzymatic activity, roach.