Aquaculture practices often expose fish to several stressors, which may activate the stress system, decreasing welfare status and negatively affecting several physiological processes, such as growth, reproduction, or immune response

The aquaculture industry has experienced considerable growth in recent decades, stimulating research into sustainable and functional feed formulations, mainly related to using high-quality, safe, and environmentally friendly feed ingredients. The employment of immunomodulatory additives is a promising strategy to enhance fish health and performance. In this study, the effects of the ghrelin analog GHRP-6 peptide included in the diet (500 µg/kg of feed) on the endocrine and immune responses of Sparus aurata following Incomplete Freund’s adjuvant (IFA) treatment were assessed. After 97 days, fish were intraperitoneally injected with 100 µL of saline solution or IFA/100 g fish and sampled 72 h post-injection. Our results indicated that fish fed GHRP-6 maintained stable plasma levels of lactate, triglycerides, and cortisol after IFA treatment, in contrast to control-fed fish, which showed significant metabolic stress. Circulating immunoglobulin levels enhanced significantly in the GHRP-6/IFA group, suggesting a stimulated humoral immune response. Transcriptomics analysis revealed that the anterior intestine was the most responsive tissue, with upregulation of il10, il15, il34, and mx1, indicating mucosal immune activation. In the spleen, GHRP-6-fed fish increased il8, il10, and ighm expression, highlighting a balanced pro- and anti-inflammatory response and support for adaptive immunity. Multivariate analysis confirmed that dietary GHRP-6 modulates immune gene expression in a tissue- and stimulus-specific manner, without inducing histological alterations in the intestine or spleen. Taken together, these preliminary results indicate that this peptide is a viable and safe dietary supplement to improve immune resilience and increase the production efficiency of S. aurata and suggest a protective effect on the fish’s immune system in this species.

Appetite regulation in fish relies on complex neuroendocrine pathways within the brain-gut axis, with ghrelin (Ghrl) and cholecystokinin (Cck) as central players. However, their spatial distribution along the gastrointestinal tract (GIT) and responses to feeding status remain poorly understood in teleosts. This study investigated: i) the baseline distribution of Ghrl and Cck levels along the GIT of juvenile Sparus aurata fed a commercial diet; ii) their temporal dynamics during short-term fasting and refeeding; and iii) the influence of diet composition on their spatiotemporal profiles. Juveniles were fed for 92 days with: i) a control diet containing 20% fishmeal (CT); ii) a plant protein diet replacing 60% of fishmeal with hydrolyzed plant protein (PP); and iii) the PP diet supplemented with 2% LB-Green _Grape functional additive (GG). Fish were sampled at 2, 6, and 24 h post-feeding (Cf), after 7 days of fasting (Ft), and at 2, 6, and 24 h post-refeeding (Rf). Hormone levels were quantified across five GIT segments, including the stomach (S1) and four equal intestinal segments (S2–S5). Baseline characterization revealed elevated Ghrl content in S3 and S5, whereas Cck levels were highest in S5. During fasting, Ghrl levels declined, while Cck increased in S1, S2, and S5 with distinct temporal patterns. After refeeding, gastric Ghrl levels (S1) decreased within 24 h, potentially reflecting secretion into plasma and involvement in hunger signaling, although plasma levels were not measured. In contrast, Cck levels in the anterior intestine (S2) rose sharply 24 h after refeeding, suggesting an anticipatory response to refeeding, possibly related to a dual role involving both rapid satiety signaling and preparatory modulation of digestive activity. The PP and GG diets maintained high gastric Ghrl (S1) and lowered intestinal Cck (S2) levels after feeding, especially in the PP diet. This pattern may either prolong satiety and reduce feed intake or reflect changes in hormone release due to lower caloric intake, with the PP diet lowering growth and feed efficiency, partially offset by the functional additive. The study maps Ghrl and Cck in the S. aurata GIT, showing spatial, temporal, and dietary regulation, with implications for aquaculture nutrition.

This study evaluated the effects of dietary fortification of high plant protein aquafeeds with two microalgae-based functional ingredients on growth, muscle composition, oxidative status, digestive function, and intestinal morphology in juvenile Sparus aurata with an average body weight of 28.4 g. Four diets were tested: a control with high fishmeal and fish oil (CTF), a plant-based diet containing 5% fishmeal and 5% fish oil (CTV), and two CTV diets supplemented with 1% LB-IMMUNOboost (IB10) or 1% LB-LIVERprotect (LP10). Fish fed CTV and LP10 showed reduced growth compared to CTF, while IB10 partially mitigated these effects. High plant dietary inclusion reduced muscle protein and increased lipid content, except in IB10-fed fish. Reduction in fishmeal and fish oil decreased muscle saturated fatty acids, EPA, and DHA. Despite similar HUFA levels in the plant-based diets, IB10 and LP10 significantly reduced lipid peroxidation, indicating a direct antioxidant effect of the functional ingredients. Digestive enzyme activities were impaired in CTV-fed fish but partially recovered in IB10 and LP10, particularly IB10. Histology revealed shorter intestinal folds and more goblet cells in high plant protein diets, especially LP10, potentially impairing absorption. Overall, microalgae-based functional ingredients, particularly LB-IMMUNOboost, partially alleviated these adverse effects, supporting their use in more sustainable aquafeed formulations.

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.