Research Progress and Application Prospects of Dietary Supplements in Growth and Immune Regulation of Aquatic Animals

The global aquaculture industry faces increasing challenges, including the need to improve feed efficiency, reduce reliance on fishmeal, and mitigate disease risks while ensuring sustainable production. Dietary supplementation has emerged as a promising strategy to address these challenges by optimizing nutrient utilization, promoting growth, and enhancing immune responses in fish and shellfish. This Special Issue has compiled 11 research articles (article 1–11) that systematically investigate the effects of dietary supplements such as glutamate, soybean isoflavones, β-1,3-glucan, yeast derivatives, α-lipoic acid, bile acid, hormones, and copper on growth performance, antioxidant capacity, immune regulation, and intestinal health in aquatic species, providing essential theoretical foundations for precision nutrition strategies. This editorial synthesizes current research advancements and outlines future directions in the field.

Metabolic regulation of functional amino acids: Glutamate is a functional amino acid that plays critical roles in nutrition, metabolism, and signaling [1,2]. In this Special Issue, Zheng et al. (article 1) found that supplementing 2% glutamate in a low-protein diet (30%) significantly increased hepatopancreatic superoxide dismutase (SOD) activity in juvenile Chinese mitten crab (Eriocheir sinensis), though it did not affect weight gain. It revealed that glutamate downregulated mTOR pathway genes (mTOR, S6K1) to inhibit protein synthesis while promoting glutathione (GSH) biosynthesis, enhancing antioxidant defenses under low-protein conditions. However, the application effect of glutamate in fish showed species differences. Jiang et al. (article 2) showed that 0.4–0.6% L-glutamic acid promoted muscle development and improved intestinal digestive enzyme activity in largemouth bass (Micropterus salmoides) by activating mTOR and PI3K/Akt pathways, suggesting that its growth-promoting effect was closely related to the metabolic characteristics of the species. These results align with findings in Jian carp (Cyprinus carpio var. Jian) [3]. Similarly, Ding et al. [4] revealed that dietary arginine had no significant effect on the growth performance of Chinese perch (Siniperca chuatsi), but significantly affected its antioxidant capacity, intestinal digestion, and nutrient metabolism. Based on the antioxidant and intestinal health indicators, the optimal dietary arginine requirement for Chinese perch was 2.99–3.37% of the dry diet. These functional amino acids play an important role in the nutrition of aquatic animals, highlighting the necessity of precise nutrition strategies.

Immune regulation and intestinal health: As an immunostimulant, β-glucan is widely used in aquatic animals to enhance immunity and promote growth [5]. In this Special Issue, Xu et al. (article 3) studied the immunomodulatory effects of β-1,3-glucan in oriental river prawn (Macrobrachium nipponense). Adding 0.2% β-1,3-glucan significantly elevated hepatopancreatic acid phosphatase (ACP) and superoxide dismutase (SOD) activities and enhanced resistance to Aeromonas hydrophila by upregulating pattern recognition receptor (PRR)-related genes (lgbp, lectin, and lbp). Intestinal microbiota analysis revealed that β-1,3-glucan suppressed Cyanobacteria abundance and promoted Rhodobacter proliferation, improving gut microbial balance. Prebiotics and probiotics have immunomodulatory effects on aquatic animals and improve their health benefits [6,7]. Gao et al. (article 4) evaluated the effects of yeast prebiotics, probiotics, postbiotics (butyrate), and black soldier fly meal (BSFM) on hepatic immune gene expression in zebrafish. The results showed that butyrate significantly downregulated pro-inflammatory cytokine expression (TNF-α and IL-1β) post-pathogen challenge, highlighting its potent anti-inflammatory properties; BSFM attenuated inflammation by suppressing the NF-κB/p65 signaling pathway, likely mediated by immune-modulating components such as chitin and antimicrobial peptides [8]. These findings provide mechanistic support for the application of butyrate and BSFL as functional feed additives. Notably, while yeast prebiotics and probiotics showed limited immunomodulatory effects, the probiotic group exhibited a downward trend in angptl4 expression following LPS challenge, suggesting indirect regulation of immune stress via lipid metabolism pathways [9]. This observation opens new avenues for exploring multi-target mechanisms of probiotics. Bile acids (BAs), the main components of bile, are initially synthesized by cholesterol in the liver and further into the intestine [10]. As one of the bile acids, taurochenodeoxycholic acid (TCDCA) is involved in nutritional regulation and has an adjuvant therapeutic effect on metabolic or immune disorders [11]. In this Special Issue, Xu et al. (article 5) demonstrated that TCDCA supplementation improved growth performance, muscle development, and nutrient quality of Procambarus clarkii, and ameliorated muscular autophagy and the gut microbiota relating to fatty acid and protein metabolism, as well as immunity. These data provide a theoretical basis for the application of TCDCA in the cultivation of crustaceans.

Antioxidant and metabolic regulation: Oxidative stress is a major constraint on aquatic animal health. α-Lipoic acid (LA) mitigated hepatic oxidative damage by scavenging free radicals (ROS) and enhancing antioxidant enzyme activities (SOD and CAT) [12]. In this Special Issue, Fang et al. (article 6) explored the effects of LA on largemouth bass fed high-carbohydrate diets. Supplementation with 0.5–1.0 g/kg LA significantly enhanced growth performance, reduced hepatic glycogen deposition, and upregulated insulin signaling molecules (ira, irb, and atk1) and glycolysis-related genes (pfkl and pk) expression through the activation of the insulin pathway, offering a novel strategy to improve carbohydrate tolerance in carnivorous fish. Soybean isoflavones are natural phytoestrogens that mainly exist in soybean and other leguminous plants. Shi et al. (article 7) investigated the effects of soybean isoflavones on growth and lipid metabolism in juvenile Chinese mitten crab. Results demonstrated that dietary supplementation with 0.004% or 0.008% soybean isoflavones significantly increased weight gain (WG) and specific growth rate (SGR) while reducing non-esterified fatty acids (NEFA) and triglyceride (TG) in the hepatopancreas. Mechanistic analysis revealed that soybean isoflavones suppressed lipid synthesis-related genes (stebp-1 and Δ9 fad) and upregulated lipolysis genes (caat, tgl, cpt-1a, cpt-1b, and cpt2), thereby improving the utilization of high-fat diets. These findings provide a theoretical basis for soybean isoflavones as functional additives in crustacean aquaculture.

Dietary hormonal additives can directly regulate the physiological state of aquatic animals and play an important role in their growth, metabolism, and immunity [13]. In this Special Issue, Liang et al. (article 8) found that triiodothyronine (T3), thyroxine (T4), and propylthiouracil (PTU) altered gut microbiota and short-chain fatty acid (SCFA) metabolism in little yellow croaker (Larimichthys polyactis). T4 treatment enhanced gut microbiota α-diversity, reduced Proteobacteria abundance, and increased Bacteroidota abundance. Acetic acid (AA) levels rose in the T3/T4 groups, whereas isobutyric acid (IBA) decreased in the T4 group. Notably, Vibrio abundance negatively correlated with AA but positively with IBA content, suggesting SCFAs modulate pathogen colonization. This work pioneers the “thyroid-gut microbiota axis” model in aquatic species, offering novel strategies for metabolic disease prevention. Melatonin, an endogenous rhythm regulator, shows promise in crustacean health management. Chen et al. (article 9) reported that dietary melatonin (50 mg/kg) in crayfish (Procambarus clarkii) synchronously enhanced diurnal non-specific immunity (lysozyme and ALP) and antioxidant capacity (CAT and GPx), while significantly upregulating mRNA expression of circadian clock genes (clock, bmal1, and per1). This study is the first to elucidate melatonin’s molecular mechanism in maintaining physiological rhythms via circadian gene regulation, providing a theoretical basis for precision feeding strategies in intensive aquaculture.

Physiological functions of trace elements: At present, the demand of largemouth bass for selenium (Se) [14], iron (Fe) [15], and zinc (Zn) [16] in feed has been reported, but the dietary appropriate level of copper (Cu) has not been reported. Cu, as an essential trace element, plays a pivotal role in antioxidant defense and immune regulation in aquatic animals. In this Special Issue, Kayiira et al. (article 10) found that dietary appropriate supplementation of Cu (3.00–3.66 mg/kg) could enhance antioxidant capacity and influence relative Nrf2 and NF-κB signaling pathways, hence improving the health and immunity of largemouth bass. Notably, excessive copper (>5.72 mg/kg) elevated plasma triglyceride (TG) content and disrupted glucose metabolism, underscoring the need for strict dosage control. This study provides essential data for standardizing copper requirements in carnivorous fish.

Dietary supplements have become an important tool for improving the health and productivity of aquatic animals by regulating growth metabolism, antioxidants, and immune pathways. This Special Issue presents a series of original research results, focusing on the latest findings in the application of aquatic animal additives, providing a theoretical basis for the precise formulation design of aquafeed, which will promote the healthy and sustainable development of the aquaculture industry.