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First published online May 30, 2008
Journal of Experimental Biology 211, 1919-1926 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.013748
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Evaluation of thyroid-mediated otolith growth of larval and juvenile tilapia

Jen-Chieh Shiao1,*, Su-Mei Wu2,*, Yi-Ping Hwang2, Done-Ping Wu3 and Pung-Pung Hwang4,{dagger}

1 Institute of Oceanography, College of Science, National Taiwan University, Taipei, Taiwan, Republic of China
2 Department of Aquatic Biosciences, College of Life Science, National Chiayi University, Chiayi, Taiwan, Republic of China
3 St Martin De Porres Hospital, Chiayi, Taiwan, Republic of China
4 Institute of Cellular and Organismic Biology, Academia Sinica, Taipei, Taiwan, Republic of China

{dagger} Author for correspondence (e-mail: pphwang{at}gate.sinica.edu.tw)

Accepted 1 April 2008

Thyroid-mediated otolith growth in tilapia was evaluated by the ontogenic triiodothyronine (T3) profile revealed by radioimmunoassay during the first month after hatching. Thyroid hormone receptor genes (TR{alpha} and TRβ) were cloned and only the expression of TR{alpha} mRNA, quantified by real-time PCR, was similar to the T3 profile. Variations in otolith growth showed median correlation with the T3 profile and TR{alpha} mRNA expression pattern. Hypothyroidism and hyperthyroidism were induced in tilapia juveniles and larvae by administration of different concentrations of thiourea (TU) and T3, respectively, for 13 days. T3 and TU had little effect on otolith growth during the larval stage. However, T3 increased otolith growth and TU retarded, or stopped, otolith growth during the juvenile stage. Furthermore, TU treatment caused permanent changes in otolith shape in the ventral area. Otolith growth recovered slowly from hypothyroidism, requiring 2 days to form an increment during the first week. These results suggest that otolith growth, at least during the juvenile stage, is regulated by the thyroid hormones and the process may be mediated by TR{alpha}.

Key words: thyroid hormone, thyroid hormone receptor, thiourea, otolith, tilapia


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