Carbaryl-induced thyroid dysfunction in the freshwater catfish Clarias batrachus

Area of Science:

• Environmental Toxicology
• Endocrinology
• Fish Biology

Background:

• Pesticide exposure, such as carbaryl, poses environmental risks to aquatic ecosystems.
• Thyroid hormones, thyroxine (T4) and triiodothyronine (T3), are crucial for fish reproduction and metabolism.
• Understanding the impact of environmental contaminants on fish endocrine systems is vital for ecological health assessments.

Purpose of the Study:

• To investigate the effects of sublethal carbaryl exposure on thyroid hormone profiles in female Clarias batrachus.
• To assess carbaryl's impact on thyroxine (T4), triiodothyronine (T3), the T3/T4 ratio, and extrathyroidal T4 to T3 conversion.
• To examine these effects during critical prespawning and spawning reproductive phases.

Main Methods:

• Female freshwater catfish (Clarias batrachus) were exposed to sublethal carbaryl concentrations (12 mg/L for 96 hr; 5 mg/L for 16 days).
• Hormone levels (T4, T3), T3/T4 ratio, and T4 to T3 conversion were measured in serum, pharyngeal thyroid, and kidney tissues.
• Measurements were taken during prespawning and spawning periods to evaluate temporal effects.

Main Results:

• Short-term (96 hr) carbaryl exposure elevated serum T3 and the T3/T4 ratio while suppressing T4.
• Long-term (16 days) exposure reduced serum T4, T3, and the T3/T4 ratio, and stimulated extrathyroidal T4 to T3 conversion.
• Carbaryl affected thyroid and kidney tissues, altering T4, T3 levels, and peroxidase activity differently based on exposure duration and tissue type.

Conclusions:

• Sublethal carbaryl exposure significantly disrupts thyroid hormone homeostasis in female catfish.
• The pesticide interferes with both thyroidal and extrathyroidal hormone production and conversion pathways.
• These endocrine-disrupting effects have potential implications for the reproductive success of Clarias batrachus.