Growth, Metabolism, and Flesh Quality in Aquaculture Nutrition

1. Introduction

Global aquaculture stands at a pivotal crossroads. As the fastest-growing food production sector, now supplying over half of all fish for human consumption, its role in global food security is undeniable. Yet, this rapid expansion brings profound challenges: the relentless pressure on finite marine resources like fishmeal and fish oil, environmental impacts of effluents and land use, animal welfare concerns, and the critical need to consistently deliver a high-quality, nutritious, and appealing product to increasingly discerning consumers. Achieving true sustainability in this context demands more than just increasing production volumes; it requires a fundamental rethinking of how we nourish farmed aquatic species. The intricate nexus between nutrition, metabolic function, growth efficiency, and the resultant flesh quality sits at the very heart of this endeavor. This special issue, “Growth, Metabolism, and Flesh Quality in Aquaculture Nutrition,” brings together a collection of cutting-edge research that probes these vital connections, offering innovative strategies and deepening our understanding for the future of responsible aquaculture.

The Special Issue focuses on the core challenges of modern aquaculture, such as optimizing growth efficiency, improving product quality, and reducing reliance on traditional feeds. Through five in-depth research articles, this Special Issue systematically explores the regulatory effects of dietary strategies—including environmental-temperature–feed combinations, alternative plant-based feeds, and functional additives—on aquatic animal growth, metabolic pathways, and flesh quality. By integrating histological, molecular, and physiological analyses, the studies provide actionable insights for precision nutrition and sustainable aquaculture. Below is a synthesis of the key contributions, knowledge gaps addressed, and future research directions.

2. Core Contributions

2.1. Environmental and Dietary Co-Regulation of Muscle Development

Angelakopoulos et al. (Article 1) investigated the interactive effects of rearing temperature and live feed types (rotifers vs. copepods) on white muscle development in greater amberjack (Seriola dumerili). The study identified that a temperature of 24 °C combined with a copepod + rotifer co-feeding scheme significantly promoted axial growth and muscle hyperplasia, as evidenced by upregulated expression of myogenic genes (mylpfb, myog) associated with muscle fiber formation and differentiation. In contrast, larvae reared at 20 °C with rotifers alone showed suppressed growth. This work fills a critical gap in understanding how abiotic and biotic factors synergistically regulate muscle development, providing a solution to growth dispersion—a major bottleneck in amberjack aquaculture.

2.2. Alternative Plant-Based Feeds for Flesh Quality Improvement

Xu et al. (Article 2) evaluated the effects of faba bean (Vicia faba L.) supplementation on GIFT tilapia (Oreochromis niloticus) muscle quality, focusing on the minimum feeding duration and post-withdrawal persistence of crispiness. Their results showed that an 8-week feeding period with a 60% faba bean diet significantly enhanced flesh hardness, chewiness, and shear force by increasing muscle fiber density and regulating genes related to muscle growth (mstn) and collagen synthesis (col1a-2). Notably, the crispy texture persisted for at least 2 months after switching back to a control diet, addressing practical needs for farmers to optimize production cycles and marketing windows. This study demonstrates the potential of plant-based feeds to improve flesh quality without compromising growth or physiological health.

2.3. Functional Additives for Growth and Health Enhancement

Three studies highlight the value of targeted feed additives in addressing aquaculture challenges: Li et al. (Article 3) explored carnosine supplementation in low-fishmeal diets for orange-spotted grouper (Epinephelus coioides). They determined that 195.14 mg/kg carnosine optimized weight gain, enhanced muscle antioxidant capacity (elevated SOD, CAT, GSH-Px; reduced MDA), and improved flesh quality by reducing water loss and enhancing texture. This provides a viable strategy to replace fishmeal while maintaining production efficiency and product quality.

Yang et al. (Article 4) focused on chlorogenic acid (CGA) supplementation for Asian swamp eel (Monopterus albus) during domestication. Using yellow mealworm as a bait carrier, they found that 500 mg/kg CGA promoted growth, modulated lipid metabolism (reduced TG and LDL; increased HDL), and enhanced non-specific immunity (elevated LZM, AKP) and antioxidant defenses (increased GSH-Px, CAT). This addresses the need for effective additives to support domestication and reduce disease risks in intensive systems.

Hu et al. (Article 5) pioneered the use of barley malt (BM) as a feed for grass carp (Ctenopharyngodon idellus). The study showed that BM improved flesh texture (hardness, gumminess) by reducing muscle fiber diameter and decreasing n-6 polyunsaturated fatty acids (PUFAs)—a modification beneficial for human health—with minimal impacts on proximate and amino acid composition. This expands the repertoire of cost-effective, sustainable alternative feeds for grass carp farming.

3. Addressed Knowledge Gaps

Prior to this Special Issue, several critical gaps hindered progress in aquaculture nutrition: limited understanding of how temperature and feed interact to regulate muscle development and growth uniformity in high-value species like greater amberjack; uncertainty regarding the minimum feeding duration for plant-based-feed-induced flesh quality traits (e.g., crispiness) and their persistence post-diet-withdrawal in tilapia; lack of data on functional additives (carnosine, CGA) for low-fishmeal diets and domestication-stage organisms, as well as novel alternative feeds (barley malt) for grass carp; and lastly, insufficient evidence on how dietary interventions modulate muscle microstructure and fatty acid profiles to align with consumer health preferences.

This Special Issue resolves these gaps by providing species-specific, mechanism-driven insights: defining optimal temperature–feed combinations for amberjack, establishing practical feeding windows for tilapia crispiness, validating additives for low-fishmeal diets, and demonstrating BM’s potential to enhance grass carp flesh quality.

4. Future Research Directions

Building on the contributions of this Special Issue, future research should focus on the following areas to advance aquaculture nutrition:

4.1. Mechanistic Deepening of Dietary Regulation

Future research should investigate the molecular pathways linking dietary components (e.g., faba bean bioactive compounds, barley malt vitamins) to muscle fiber remodeling and collagen synthesis, using multi-omics approaches (transcriptomics and metabolomics) to uncover key regulatory networks. Epigenetic modifications induced by temperature–feed interactions in greater amberjack should be explored, particularly regarding myogenic gene expression and size disparity, to develop targeted breeding and feeding strategies.

4.2. Optimization of Feed Formulations and Additive Application

Future research should evaluate the long-term effects of carnosine, CGA, and barley malt on growth, disease resistance, and environmental sustainability across different aquaculture systems (e.g., recirculating aquaculture systems and pond culture); develop blended feed formulations (e.g., faba bean + barley malt) to synergistically enhance flesh quality, reduce feed costs, and minimize environmental impacts (e.g., nitrogen and phosphorus excretion); and determine species-specific optimal dosages and application timings for functional additives, considering developmental stages (e.g., larvae vs. juveniles) and environmental conditions (e.g., temperature, salinity).

4.3. Scalability and Practical Application

Large-scale field trials should be conducted to validate laboratory findings, particularly for barley malt and faba bean diets, to ensure compatibility with commercial production practices and economic viability. Also, user-friendly feeding guidelines need to be developed for farmers, integrating insights into minimum feeding durations, post-withdrawal quality persistence, and additive dosage control.

4.4. Integration of Nutrition with Sustainable Aquaculture

Future research should explore how dietary strategies can mitigate climate change impacts (e.g., temperature fluctuations) on aquatic animals, building on the temperature–feed interaction data gathered for greater amberjack. The role of functional feeds and alternative plant-based diets in reducing antibiotic use by enhancing immune function should be investigated, particularly in intensive production systems.

4.5. Consumer-Centric Quality Traits

Dietary modulation of fatty acid profiles (e.g., reducing n-6 PUFAs and increasing n-3 PUFAs) could be further optimized to meet human health recommendations, and the sensory traits (e.g., flavor, aroma) affected by alternative feeds should be evaluated. Future research should assess the shelf-life and processing stability of flesh quality traits induced by dietary interventions (e.g., tilapia crispiness and grass carp texture) to enhance market competitiveness.

5. Conclusions

This Special Issue provides a comprehensive update on the role of nutrition in regulating growth, metabolism, and flesh quality in aquaculture. The five studies offer practical solutions for producers while advancing our understanding of underlying physiological and molecular mechanisms. As aquaculture continues to expand to meet global food demand, future research should build on these findings to develop sustainable, efficient, and consumer-friendly nutrition strategies. We thank all of the authors, reviewers, and readers for their contributions, and we anticipate that this Special Issue will stimulate further innovation in aquaculture nutrition.