| Summary: | In all vertebrates thyroid hormones are essential for normal growth, metabolism, and development. Thyroid hormones are unusual in that they require iodine to function. While the pathway of iodide uptake in terrestrial vertebrates has been established to be strictly dietary, and is mediated by the same sodium-iodide symporter (NIS) protein that concentrates iodine in the thyroid, the method of iodine uptake in fish remains controversial. In this study, I attempted to contrast the expression of a potential orthologue of NIS in two species of teleost fish, the red drum (Sciaenops ocellatus), a marine species living in an iodide rich environment, and the zebrafish (Danio rerio), a freshwater species living in an iodide poor environment. I applied RT-PCR to the digestive tract, the subpharyngeal region, and the gill, to determine whether fish in low iodine environments may possess a more active branchial iodide uptake pathway. I found that red drum held at higher salinities lack significant expression of nis in the gill but did not successfully identify the expression pattern of nis in zebrafish. Further research is needed to accomplish this goal.
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