Dietary Supplementation with Chenodeoxycholic Acid or Ursodeoxycholic Acid Modulates Growth, Thyroid Status, and Hepatopancreatic–Intestinal Health in Juvenile Little Yellow Croaker Larimichthys polyactis

Commercial feeds formulated for <i>Larimichthys crocea</i> are commonly used in intensive farming of <i>Larimichthys polyactis</i>; however, their nutritional composition is suboptimal for the latter. The study evaluated the effects of dietary chenodeoxycholic acid (CDCA) and ursodeoxycholic acid (UDCA) supplementation on mitigating nutritional mismatch-induced growth retardation and hepatopancreatic-intestinal metabolic disorders in <i>L. polyactis</i>. Fish were fed seven feeds: a commercial feed (control) and feeds supplemented with 300, 600, and 1200 mg/kg of CDCA or UDCA. Results showed that both bile acids (BAs) supplementation improved growth, altered thyroid hormone metabolism, with significant changes in hepatopancreatic-intestinal types of deiodination. Both BAs increased hepatopancreatic energy metabolism and cholic acid synthesis, while inducing hepatopancreatic oxidative damage. Notably, 300 mg/kg CDCA and 600 mg/kg UDCA significantly reduced hepatopancreatic vacuolation and lipid accumulation, which was associated with enhanced protease and lipase activities (<i>p</i> < 0.05). Dietary both BAs supplementation enhanced intestinal antioxidant capacity, but contributed to the inflammation, with 300 mg/kg UDCA improving intestinal mucosal morphology (<i>p</i> < 0.05). These findings suggest that supplementation with dietary 300 mg/kg CDCA, 300 and 600 mg/kg UDCA could alleviate growth restriction and liver-intestinal structural damage caused by nutritional mismatch, reduce hepatic fat accumulation, and enhance intestinal antioxidant capacity of <i>L. polyactis</i>.