Goiter, a pathologic enlargement of the thyroid gland, is a significant disease of captive sharks, and causes morbidity (e.g., goiter rupture, anorexia) and mortality.1 A longstanding hypothesis with respect to the underlying cause of goiter in sharks maintains that goiter results from insufficient iodine in the diet or tank water; however, results of recent studies demonstrated that other factors, such as nitrates, may contribute to the development of goiter in sharks.2 The role of iodine in normal shark thyroid physiology is currently uncertain, and definitive recommendations regarding iodine supplementation (e.g., oral versus tank water supplementation, accurate supplement quantity) cannot be made at this time. In order to determine the interaction between iodine supplementation and serum thyroid hormone concentrations, healthy adult, white-spotted bamboo sharks (Chiloscyllium plagiosum) (n=28) were enrolled in this study. Four groups of sharks (n=7 per group) received one of the following iodine supplementation protocols: 1) no iodine supplementation; 2) oral iodine supplementation; 3) water iodine supplementation; or 4) both oral and water iodine supplementation. Results suggested that serum T4 concentrations were more consistent in sharks that received oral and water supplementation. In addition, serum T3 concentrations were significantly decreased in sharks receiving oral supplementation. Based on these results, it appears iodine supplementation alters the thyroid hormone concentrations of captive white-spotted bamboo sharks, and that both oral and water supplementation may play a role in appropriate iodine supplementation.
1. Janse M, Firchau B, Mohan PJ. Elasmobranch nutrition, food handling, and feeding techniques. In: Smith M, Warmolts D, Thoney D, Hueter R, eds. The Elasmobranch Husbandry Manual: Captive Care of Sharks, Rays, and their Relatives. Columbus, OH: Ohio Biological Survey; 2004:183–200.
2. Morris, AL, Hamlin, HJ, Francis-Floyd, R, Sheppard, BJ, Guillette, LJ. Nitrate-induced goiter in captive whitespotted bamboo sharks Chiloscyllium plagiosum. J Aquat Anim Health. 2011;23(2):92–99.