Fasting Reveals the Effects of a Plant Extract- and Microalgae-Derived Nutraceutical on Lipid Metabolism and Hepatic Physiology in Juvenile Sparus aurata Fed a Plant-Based Diet.

This study investigated the effects of a plant-based diet supplemented with a nutraceutical derived from plant extracts and microalgae on hepatic function and lipid metabolism during a fasting challenge. Juvenile Sparus aurata were fed three experimental diets for 90 days, followed by 14 days of feed deprivation. The diets consisted of: (i) a control formulation representative of commercial feeds for the species (C+: 20% fishmeal [FM], 9% fish oil [FO]); (ii) a low-FM, predominantly plant-based diet containing 5% FM and 5% FO (C‒); and (iii) the same C‒ diet supplemented with 1% LB-LIVERprotect nutraceutical (LP). LP supplementation improved specific aspects of fatty acid composition in mesenteric fat, including eicosapentaenoic acid (EPA) content and the omega-3/omega-6 ratio. These changes were potentially associated with increased hepatic expression of desaturases (fads2 and scd1a). Fish in the LP group also exhibited a higher mesenteric index (MSI), together with hepatic upregulation of key genes involved in lipid catabolism (lpl, hl, atgl, and hsl). Following feed deprivation, a marked reduction in both MSI and the expression of lipid catabolic genes supported active mobilization of mesenteric fat in LP-fed fish. This response was accompanied by signs of hepatic protection during fasting, including preserved energy reserves, a higher hepatosomatic index (HSI), and reduced hepatocyte atrophy. Moreover, LP supplementation partially attenuated several adverse effects observed in the C‒ group, such as elevated plasma cortisol levels and increased indicators of energy demand during fasting. Consistently, LP-fed fish showed fewer signs of fasting-induced liver damage, as reflected by an approximately 3.4-fold lower plasma alanine aminotransferase (ALT) activity compared to the C‒ group. Overall, LB-LIVERprotect shows potential to support fish health and tissue integrity during feed deprivation and to mitigate some of the negative effects associated with plant-based aquafeeds.