Relationship of Water Chemistry to Serum ThyroidHormones in Captive Sharks with Goitres

Abstract

Captive whitetip reef sharks, Triaenodon obesus,at Sea Life Park (SLP) Hawaii, Waimanalo, Hawaii develop goitre, whereas, T. obesus at the Waikiki Aquarium (WAQ), Honolulu,Hawaii do not develop goitre. To determine theeffects of natural concentrations of iodine on thereduction of goitre, two sharks from SLP with goitrewere placed in an enclosed coastal lagoon with naturalseawater. Using ultrasound measurements the twogoitres were initially 11.4 cm and 14.6 cm in depthand after 3 months decreased to 4.7 cm and 5.7 cm. Radioimmunoassay analysis of the thyroid hormoneT3 sera concentrations were initially 0.22 ng/mland 0.33 ng/ml and increased to 1.84 ng/ml after beingplaced in the lagoon. Sera T4 were initially0.93 ng/ml and 0.99 ng/ml and increased dramaticallyto 17 ng/ml and 56 ng/ml. Over the six month samplingperiod, two resident sharks in the lagoon with normalthyroids had sera T3 concentrations from 0.89ng/ml to 1.1 ng/ml, and sera T4 concentrationsfrom 3.1 ng/ml to 7.9 ng/ml. The hypothyroidcondition in the SLP goitred-sharks is likely linkedto the low environmental iodide (<0.005 μM), andhigh nitrate (111 μM) of SLP water. The WAQwell-water facility was characterized by anoxic waterwith high iodide (0.60 μM), total iodine (1.90μM), and typical nitrate (24.6 μM)concentrations of interstitial groundwater. Thedifference of iodide concentration of SLP and WAQ tankwater (<0.005 μM versus 0.60 μM) wasdirectly related to the hydrogeology of the well-watersources. To avoid goitre in marine aquarium systems,we recommend maintaining iodide concentrations of atleast 0.15 μM.