Chitosan as a Fish Feed Additive: Enhancing Aquaculture Performance and Sustainability

From insects to schools: chitosan‑powered feed boosts growth, immunity and stress resilience for healthier, more sustainable aquaculture

Introduction

The global aquaculture industry faces persistent challenges in meeting the escalating demand for seafood while ensuring sustainable practices. As production intensifies, fish farmers grapple with issues such as disease outbreaks, environmental stressors, and the need for efficient feed utilisation. In this context, the exploration of novel, natural feed additives has become a priority. Chitosan, a versatile biopolymer derived from chitin, has emerged as a promising solution with remarkable potential to enhance fish health, growth, and overall aquaculture sustainability. This article delves into the multifaceted benefits of chitosan as a fish feed supplement, examining its role in improving growth performance, boosting immune function, and increasing stress resilience in farmed fish.

Chitosan: Nature's Versatile Biopolymer

Chitosan is a linear polysaccharide composed primarily of randomly distributed β-(1→4)-linked D-glucosamine and N-acetyl-D-glucosamine units. It is obtained through the deacetylation of chitin, the second most abundant biopolymer on Earth, found predominantly in the exoskeletons of crustaceans, insects, and fungal cell walls. This unique molecular structure, characterised by a positive charge in acidic conditions, enables chitosan to interact effectively with negatively charged molecules, cells, and surfaces. These properties confer a range of biological activities, including biocompatibility, biodegradability, and non-toxicity, making chitosan an ideal candidate for enhancing fish health and performance in aquaculture settings.

Enhancing Growth Performance

Chitosan supplementation in tilapia feed significantly boosts growth rate, feed efficiency and nutrient absorption, helping farmed fish achieve healthier weights and improved productivity

One of the most significant benefits of chitosan supplementation in fish feed is its ability to enhance growth performance. Numerous scientific studies have documented improvements in weight gain, specific growth rate, and feed conversion ratio in various fish species fed with chitosan-enriched diets. For instance, research by Yu et al. (2023) demonstrated that dietary chitosan significantly enhanced weight gain in fish, with optimal results observed at a specific inclusion level. Similarly, Zhang et al. (2024) conducted a comprehensive study on juvenile tilapia (Oreochromis niloticus) and found that dietary chitosan significantly increased final weight, weight gain rate, specific growth rate, and daily growth index. The researchers observed that the optimal dietary chitosan level for juvenile tilapia was approximately 1.42% to 1.45%, which resulted in the most favourable growth outcomes. These growth-promoting effects can be attributed to several mechanisms:

1. Improved Nutrient Digestibility: Chitosan enhances the activity of digestive enzymes such as amylase, lipase, and protease, leading to better nutrient utilisation. Eissa et al. (2024) demonstrated that chitosan nanoparticles significantly increased digestive enzyme activities in white leg shrimp, resulting in improved feed conversion and growth.

2. Enhanced Gut Health: Chitosan acts as a prebiotic, promoting the growth of beneficial gut microbiota while inhibiting pathogenic bacteria. This creates a healthier intestinal environment that facilitates nutrient absorption and reduces energy expenditure on immune responses.

3. Reduced Oxidative Stress: The antioxidant properties of chitosan help neutralise reactive oxygen species that can damage cellular components and impair growth. By reducing oxidative stress, chitosan allows fish to allocate more energy toward growth rather than cellular repair.

4. Hormonal Regulation: Some studies suggest that chitosan may influence the secretion of growth-related hormones, further contributing to enhanced growth performance.

Boosting Immune Function

Chitosan strengthens fish immune defences, enhancing lysozyme production, activating innate immunity, and improving resistance against pathogens, supporting healthier, disease-resilient aquaculture populations

Disease outbreaks represent one of the most significant threats to aquaculture operations, causing substantial economic losses and compromising animal welfare. Chitosan has demonstrated remarkable immunostimulatory properties that can enhance fish resistance to pathogens and reduce disease incidence. The immune-enhancing effects of chitosan have been well-documented in scientific literature. Zhang et al. (2024) reported that dietary chitosan significantly increased the activities of lysozyme and other immune-related enzymes in juvenile tilapia. Lysozyme is an important component of the innate immune system, capable of breaking down bacterial cell walls and providing protection against infections. Abdel-Ghany & Salem (2020) showed that fish fed with chitosan-enriched diets exhibited higher levels of lysozyme and complement proteins, both crucial components of the immune system. This immune enhancement leads to improved survival rates and overall health in aquaculture settings. Chitosan's immunostimulatory effects operate through several pathways:

1. Activation of Macrophages: Chitosan induces the activation of macrophages and other immune cells, leading to increased phagocytic activity and the production of antimicrobial peptides. These peptides play a critical role in innate immunity, enhancing the host's ability to combat infections.

2. Modulation of Cytokine Production: Research indicates that chitosan can influence the expression of cytokines, which are signalling molecules that regulate immune responses. Zhang et al. (2024) found that dietary chitosan significantly down-regulated pro-inflammatory cytokines (IL-6, IL-8, TNF-α) while up-regulating anti-inflammatory cytokines (IL-10), creating a balanced immune environment.

3. Enhancement of Mucosal Immunity: Chitosan strengthens the mucosal barriers in fish, which serve as the first line of defence against pathogens. This includes increased production of mucus and antimicrobial compounds at mucosal surfaces.

4. Complement System Activation: Some studies suggest that chitosan can activate the complement system, a part of the immune system that enhances the ability of antibodies and phagocytic cells to clear pathogens.

By boosting immune function through these mechanisms, chitosan helps reduce the reliance on antibiotics in aquaculture, addressing concerns about antibiotic resistance and promoting more sustainable farming practices.

Increasing Stress Resilience

Stress is an inevitable aspect of intensive aquaculture systems, arising from factors such as high stocking densities, handling, transport, poor water quality, and temperature fluctuations. Chronic stress can suppress immune function, impair growth, and increase susceptibility to diseases, ultimately affecting production outcomes. Chitosan has shown promising results in enhancing stress resilience in farmed fish, helping them cope better with challenging environmental conditions. El-Naggar et al. (2021) demonstrated that chitosan supplementation enhanced the immune response in fish, helping them to better cope with stressful conditions. Furthermore, chitosan has been shown to act as an antioxidant, reducing oxidative stress in aquatic species. By administering chitosan in feed, aquaculture operators can improve fish resilience to environmental stressors, promoting overall welfare and productivity. The stress-mitigating effects of chitosan can be attributed to several mechanisms:

1. Antioxidant Defence: Chitosan enhances the activity of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GSH-Px), which neutralise reactive oxygen species generated during stress. Zhang et al. (2024) observed that dietary chitosan significantly increased the activities of SOD and CAT while decreasing malondialdehyde (MDA) levels, indicating reduced oxidative damage.

2. Osmoregulatory Support: Chitosan has been shown to improve osmoregulatory capacity in fish exposed to salinity stress by enhancing the activity of Na+, K+-ATPase and other ion-transporting enzymes. This helps maintain ionic balance and reduces the metabolic cost of adaptation to changing environments.

3. Cortisol Regulation: Some studies suggest that chitosan may modulate cortisol levels, the primary stress hormone in fish. By preventing excessive cortisol secretion during stress, chitosan helps minimise the negative impacts of stress on growth, reproduction, and immune function.

4. Cellular Protection: The bioactive properties of chitosan provide protection to cellular components against stress-induced damage, maintaining tissue integrity and function under challenging conditions.

Practical Applications in Aquaculture

The benefits of chitosan for fish feed supplementation extend beyond laboratory findings to practical applications in commercial aquaculture. Incorporating chitosan into fish feed formulations can be accomplished through various methods, depending on the specific requirements and constraints of the operation. Chitosan can be added directly to feed formulations during the manufacturing process, ensuring uniform distribution and stability. Alternatively, it can be applied as a coating on feed pellets, which may enhance palatability and protect the active compounds from degradation. Recent advancements in nanotechnology have led to the development of chitosan nanoparticles, which offer improved bioavailability and efficacy compared to conventional forms.

The optimal inclusion rate of chitosan in fish feed varies depending on the species, life stage, and specific objectives. Based on scientific studies, inclusion rates typically range from 0.5% to 2% of the diet, with most beneficial effects observed around 1.5%. Zhang et al. (2024) determined that the optimal dietary chitosan level for juvenile tilapia was approximately 1.42% to 1.45%, which provides a useful reference point for feed formulation. When implementing chitosan supplementation in aquaculture operations, several factors should be considered:

1. Quality and Source: The quality of chitosan can vary significantly depending on the source material and production process. High-quality chitosan with a defined degree of deacetylation and molecular weight is essential for consistent results.

2. Cost-Benefit Analysis: While chitosan supplementation incurs additional feed costs, these are often offset by improved growth performance, reduced mortality, and decreased medication expenses. A comprehensive cost-benefit analysis should be conducted to determine the economic viability for specific operations.

3. Integration with Existing Practices: Chitosan supplementation should be integrated with good management practices, including proper water quality maintenance, appropriate stocking densities, and regular health monitoring, to maximise its benefits.

4. Regulatory Considerations: Aquaculture operators should ensure compliance with local regulations regarding feed additives and supplements when incorporating chitosan into their feeding regimes.

Chitosan can be directly incorporated into commercial fish feed or used as a biodegradable coating for pellets, supporting efficient nutrient delivery and improved water quality, making it ideal for large-scale aquaculture operations

By carefully considering these factors, aquaculture producers can effectively harness the benefits of chitosan to enhance their operations' productivity, sustainability, and profitability.

Conclusion

Chitosan stands as a transformative biopolymer with immense potential to revolutionise the aquaculture industry. Its proven ability to enhance growth performance, bolster immune function, and improve stress resilience in farmed fish offers a sustainable and economically viable solution to many of the challenges facing modern aquaculture. By integrating chitosan into feed formulations, producers can achieve healthier fish, reduce reliance on antibiotics, and improve overall productivity and profitability.

Entoplast, as a leading manufacturer of high-quality chitin and chitosan, is at the forefront of this innovation. Our commitment to sustainable production and rigorous quality control ensures that our chitosan products are of the highest standard, tailored to meet the specific needs of the aquaculture sector. We invite scientists, academics, and industry experts to partner with Entoplast to explore the full potential of chitosan and drive forward the next generation of sustainable aquaculture solutions. Contact us today to discuss potential collaborations or investments in our cutting-edge product lines.