Thyroid-Active Agents Triiodothyronine, Thyroxine and Propylthiouracil Differentially Affect Growth, Intestinal Short Chain Fatty Acids and Microbiota in Little Yellow Croaker Larimichthys polyactis

Thyroid dysfunction may affect the intestinal microbiota through short-chain fatty acids (SCFAs) in marine fish. This study investigated the effects of triiodothyronine (T3, 20 ng/g) and thyroxine (T4, 20 ng/g), and propylthiouracil (PTU, 5000 ng/g) on growth performance, intestinal SCFA profiles, and microbiota composition in little yellow croakers Larimichthys polyactis. The results showed that dietary thyroid-active agent supplementation significantly decreased weight gain, and specific growth ratio. Moreover, dietary T3, T4, and PTU induced the states of hyperthyroidism, hyperthyroidism, and hypothyroidism, respectively, leading to differential alterations in intestinal SCFA profiles. Specifically, only dietary T4 supplementation significantly increased the diversity of intestinal microbiota. Our findings suggest that the genera Vibrio and Sediminibacterium play key roles in multiple metabolic pathways within the host intestine. Correlation analyses further indicated that intestinal acetic acid and isobutyric acid were characteristic metabolites involved in the alteration of the genus Vibrio abundance. These results provide a foundation for further investigation into the effects of thyroid-disrupting activities on growth, intestinal SCFA profiles, and microbiota composition in marine fish.