Dietary Herbal Leaves Mixture Extract Enhances Growth, Antioxidant Status, and Resistance to <i>Gyrodactylus malalai</i> in Heteroclarias Catfish, <i>Clarias gariepinus ♀</i>  ×  <i>Heterobranchus longifilis ♂</i>

<i>Gyrodactylus malalai</i> commonly attacks fish gills, which can swiftly infect entire fish stocks and cause both biological and monetary losses. The most popular treatment for <i>G. malalai</i> infestations in fish farms is chemotherapy; however, these drugs can have major side effects and are expensive. Novel and ecologically friendly treatments are necessary to treat and control such parasite infestations in fish. Our study examined the use of an herbal leaf mixture extract of <i>Tridax procumbens</i>, <i>Mitrascapus scaber</i>, <i>Mucuna pruriens</i>, and <i>Carica papaya</i> (EML) as a functional feed supplement to manage this possible parasite infection. We prepared five distinct isonitrogenous diets (400 g/kg crude protein [CP]) supplemented with 0, 2, 4, 6, or 8 g EML/kg. Juveniles of <i>Clarias gariepinus</i> ♀ × <i>Heterobranchus longifilis</i> ♂ (heteroclarias, mean weight = 14.5 g) were fed with designated feed six times a day for 56 days until they seemed satisfied. Followed by a 14-day exposure to <i>G. malalai</i> (NCBI: txid905034; 40 individuals/L of water), fish in each treatment were monitored closely for any clinical symptoms and mortality. Fish fed EML-enriched diets showed significantly (<i>p</i> < 0.05) improved growth performance, showing trend in a dose-dependent order with an optimum value of 5.94 g EML/kg. Intestinal histomorphometry, digesta pH, viscosity, and short-chain fatty acid (SCFA) were significantly higher (<i>p</i> < 0.05) in EML-fed fish in a dose-dependent manner. Furthermore, an enhanced hematological profile was noticed in fish fed on enriched diet, while urea (UREA), creatinine (CREAT), glucose (GLU), and cholesterol (CHOL) levels decreased in fish fed diets supplemented with EML levels than the control (<i>p</i> < 0.05). Antioxidant status and immune response were promoted in fish fed fortified diet (<i>p</i> < 0.05). Postinfestation survival was highest at 8 g EML/kg (80.00%) compared to control (47.50%). The study concluded that EML improved the hemato-biochemical profile and growth performance of heteroclarias without having any major negative effects, as well as protection against <i>Gyrodactylus malalai</i> infestation with an optimum level of 5.94 g/kg. This study is the first to report the use of a standardized herbal leaf mixture extract (EML) comprising <i>T. procumbens</i>, <i>M. scaber</i>, <i>M. pruriens</i>, and <i>C. papaya</i> as a practical and functional dietary supplement for the management of <i>Gyrodactylus malalai</i> infestation in heteroclarias, documenting novel evidence of the dual role of EML in promoting growth performance and enhancing improving postinfestation survival.