Elasmobranch susceptibility to
goiter formation in captive environments has been well documented. Until recently, most public aquariums operated under the belief that the etiology of
goiter in elasmobranchs was nutritional and specifically caused by insufficient dietary
iodine. Recent studies have demonstrated that high environmental
nitrate (NO3-N) inhibits the ability of the thyroid gland to utilize available
iodide, resulting in thyroid gland overstimulation by
thyroid stimulating hormone and ultimately leading to the development of
goiter. The objective of this study was to evaluate the effects of high environmental
nitrate concentrations on thyroid function in juvenile whitespotted bamboo sharks Chiloscyllium plagiosum. In July 2008, five juveniles (80-150 g) were exposed to a low-
nitrate environment (NO3-N concentration < 1 mg/L of water) and five were exposed to an elevated-
nitrate environment (NO3-N = 70 mg/L) for 29 d in a flow-through natural seawater system.
Nitrate exposure did not affect growth rates (e.g., weight, length, and condition factor) and did not alter free plasma
thyroxine concentrations during the 29-d experimental period. However, histological examination of thyroid glands from sharks exposed to elevated
nitrate revealed the development of diffuse hyperplastic
goiter. With increasing restrictions on water use, most modern aquaria operate as recirculating systems, which results in higher and more chronic
nitrate exposure for captive animals.
Goiter is one of the most common health problems in captive elasmobranchs, and this study suggests that
nitrate exposure is an important factor in the etiology of this disease.