Evaluation of thyroid-mediated otolith growth of larval and juvenile tilapia.
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 (TRalpha and TRbeta) were cloned and only the expression of TRalpha mRNA, quantified by real-time PCR, was similar to the T3 profile. Variations in otolith growth showed median correlation with the T3 profile and TRalpha 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 TRalpha.
Institute of Oceanography, College of Science, National Taiwan University, Taipei, Taiwan, Republic of China.
Jen-Chieh
JC
Shiao
Su-Mei
SM
Wu
Yi-Ping
YP
Hwang
Done-Ping
DP
Wu
Pung-Pung
PP
Hwang
D000704:Analysis of Variance; D000818:Animals; D017931:DNA Primers / Q000235:genetics; D010037:Otolithic Membrane / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism; D011863:Radioimmunoassay; D011988:Receptors, Thyroid Hormone / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013890:Thiourea / Q000494:pharmacology; D017210:Tilapia / Q000502:physiology*; D014284:Triiodothyronine / Q000378:metabolism* / Q000494:pharmacology
D017931:DNA Primers; D011988:Receptors, Thyroid Hormone; D014284:Triiodothyronine; D013890:Thiourea