From feed to immunity: a focus on fish and shrimp health

Nucleotide Supplementation: Boosting Immunity and Recovery in Aquaculture

During disease states and injury, the rapid cell proliferation required for cellular immune responses and tissue healing leads to nucleotide depletion. Nucleotides are the basic building blocks for the synthesis of DNA, RNA, ATP, and key coenzymes involved in essential metabolic processes. The cells of the immune system and the gastrointestinal tract are those most affected by shortfalls in the supply of nucleotides. Nucleotide synthesis is an energy intensive process that uses multiple metabolic pathways across different cell compartments and requires a variety of carbon and nitrogen sources. Moreover, nucleotide levels in diets have been declining in recent years due to a shift in feed formulations from marine to vegetable ingredients. To address this, dietary supplementation with nucleotides can be beneficial, particularly under conditions of rapid growth, stress, or disease. Nucleotides are the building blocks for essential cellular processes and their supplementation helps spare energy costs and optimize the function of rapidly dividing tissues like the gut and immune system. A highly purified nucleotide source, such as Rovimax®, has been shown to improve gut health, accelerate healing after injuries, and significantly enhance (up to 30%) both innate and adaptive immune responses in fish and shrimp*. This translates to higher survival rates when faced with pathogens. For example, studies have shown that Rovimax® supplementation increases resistance to bacterial diseases by over 20% in seabass against Listonella anguillarum and over 40% in tilapia and shrimp against Streptococcus iniae and Vibrio parahaemolyticus, respectively*.

How Vitamins Support Optimal Immunity in Aquaculture

Vitamins essential for the generation of energy reserves necessary to mount immune responses and play specific and vital functions within the immune cell population. To set the best nutritional foundations for optimal aquaculture production we provide our Optimal Vitamin Nutrition™ guidelines (OVN®).

• B vitamins, including thiamine (B1), riboflavin (B2), niacin (B3), and others, act as co-pilots for numerous enzymes and fuel various metabolic pathways, including energy production. This is especially important for the immune system, which can consume a significant portion of an animal's energy reserves – up to 25% under normal conditions and even more when fighting off infections.
• Vitamin D plays a key role in the proliferation, differentiation, and regulation of immune cells and is also implicated in humoral responses. Immunoglobulins, complement proteins and antimicrobial peptides, including lysozyme, are all influenced by the actions of the vitamin D system. The recruitment of neutrophils to sites of infection or injury also depends on vitamin D. Recent in vitro studies have shown that D3 reduces the attachment and invasion of gram-negative bacteria to Atlantic salmon macrophages. In shrimp, the increased expression of antimicrobial peptides with D3 reduces the colonisation of Vibrio parahaemolyticus in the digestive tract. Recent dsm-firmenich studies showed improved resistance to bacterial pathogens by using ROVIMIX® HyD®, a more potent form of vitamin D.
• Vitamin E plays a fundamental role in the cellular component of the immune system by its antioxidant protection of cell membranes against oxidation. The potency of this antioxidant is increased by a synergy with the selenium-containing enzyme glutathione peroxidase. This protective effect is evidenced by the decrease of red blood cell fragility in fish with higher levels of plasma α-tocopherol, the active form of vitamin E in ROVIMIX® E50. Vitamin E also functions in the modulation of cell signalling, particularly those regulating immune antioxidant responses. Humoral responses also depend on dietary supplies of vitamin E. Responses of both the specific and innate immune systems are enhanced by increased supplementation of vitamin E. Several studies across a diversity of aquatic species have demonstrated a reduced disease resistance with vitamin E deficiency. On the contrary, higher levels of dietary vitamin E have been shown to enhance resistance to infectious diseases. Vitamin E supports the production of lysozyme with benefits on survival against bacterial infections. Enhancing feed levels of vitamin E in aquatic species has been shown to increase white blood cell counts, respiratory burst capability, and the activity of the alternative complement pathway.

Astaxanthin (active component in CAROPHYLL® Pink is well known for its role in the pigmentation of both salmonids and shrimp, but its functions in the immune system are less well recognised. The molecular structure of astaxanthin gives it unique properties that make it the most potent antioxidant known for the protection of cell membranes. It is no surprise that dsm-firmenich studies have detected the presence of astaxanthin in the innate immune cells. The highest concentration of astaxanthin is in the macrophages, which are typically first responder cells performing their functions in highly oxidised tissues. The protection of macrophages by astaxanthin in these challenging environments has positive impacts on their phagocytic capability. The presence of astaxanthin in immune cells increases resistance to both viral and bacterial disease. In juvenile salmonids, astaxanthin increases resistance to both bacterial and viral pathogens and in Penaeus vannamei shrimp astaxanthin improves resistance to Early Mortality Syndrome (EMS) caused by Vibrio parahaemolyticus.

• Vitamin C (ascorbic acid) is also known for its role in the immune function of both fish and shrimp. The reduced disease resistance associated with vitamin C deficiency has been documented in several aquatic species. For extruded feeds, ascorbic acid phosphate, the active form in STAY-C® 50 offers the best combination of stability and bioavailability. Vitamin C performs antioxidant functions in hydrophilic cellular environments and is also known for its regeneration of membrane-bound vitamin E. In the innate immune system, vitamin C is involved in the cellular component for leucocyte proliferation, phagocytosis & chemotaxis. Humoral responses including lysozyme & complement proteins also rely on an optimal dietary supply of vitamin C. Vitamin C is also required for immunoglobulin production by the adaptive immune system.

Conclusion

Immunity is a complex topic, but it is key to supporting a robust animal against a range of biological, physiological, and environmental stressors. Ensuring optimum vitamin level with OVN® is fundamental and even suboptimal levels can lead to reduced health*, performance, and welfare. During periods of stress or increased disease risk, aquatic animals need additional nutritional support to maximize survival and growth performance. For this extra boost, Rovimax® delivers biologically available nucleotides quickly and directly to the gut with minimal energy investment, for maximum benefits in aquatic animals. Acting in concert, an optimal vitamin intake ensures production animals have a robust immune function that enables performance and survival in challenging conditions.

*According to dsm-firmenich in vivo feeding trials.