Development of thyroid abnormalities in mummichogs, Fundulus heteroclitus, from a polluted site

Area of Science:

• Environmental toxicology
• Developmental biology
• Endocrinology

Background:

• Previous studies identified enlarged thyroid follicles and elevated thyroxine in adult and 6-month-old Fundulus heteroclitus from polluted sites.
• These abnormalities were compared to those found in fish from unpolluted reference sites.

Purpose of the Study:

• To determine the developmental stage at which thyroid abnormalities first appear in Fundulus heteroclitus exposed to pollution.
• To investigate the onset of enlarged thyroid follicles and altered thyroxine levels during early development.

Main Methods:

• Comparative analysis of thyroid follicle size in Fundulus heteroclitus of varying sizes (12-25 mm) from polluted and unpolluted sites.
• Radioimmunoassay measurements of thyroxine levels in different size classes of fish.

Main Results:

• Fundulus heteroclitus of 15-20 mm from polluted sites exhibited significantly larger thyroid follicles, mirroring patterns in older fish.
• A reversal was observed in smaller fish (12-14.5 mm), with polluted populations showing smaller average follicle size.
• Thyroxine levels, while not statistically significant, generally aligned with follicle size differences, being higher in larger polluted-site fish and lower in smaller ones.

Conclusions:

• Thyroid abnormalities, characterized by enlarged follicles, manifest in Fundulus heteroclitus around 15-20 mm in length.
• A follicle size reversal in the 12-14.5 mm size range suggests potential thyroid disruption may occur even earlier in development.