Particularities of the Shrimp Immune System: What are the Impacts on Overall Stress Resistance in Shrimp Farming?

Shrimp do not have the same immune system as vertebrates. This characteristic has a significant impact on shrimp farm management: it prevents these crustaceans from becoming immune to disease through vaccination. Since shrimp lack an adaptive immune system, innate immunity is their essential form of defense. This immunity acts as first-line protection from the disease and mortality threats that can potentially affect prawn stocks. How does the shrimp immune system function?  How can its defenses be stimulated for reducing the overall impact of stress on shrimp farms?

Shrimp are animals whose immune system differs considerably from that of vertebrates. This specificity has a direct impact on shrimp farming. Indeed, shrimp cannot be vaccinated. Therefore, new disease outbreaks such as the White Spot Syndrome Virus, the Taura virus, the Yellow Head Virus or, more recently, the Early Mortality Syndrome, are always considered to be major events in the industry.
 

Particularities of the shrimp immune system

Animals are endowed with various types of defense systems, as follows: physical barriers such as skin, mucus, the exoskeleton, and the microflora; innate immunity: this form of immunity is common to vertebrates and shrimp. It is generic, non-specific, reactive, and oriented towards what is the 'non-self', i.e. external aggressions. It acts as a first line of defense; acquired immunity: this form of immunity is highly specific of a given pathogen. Crustaceans are devoid of it.

The very principle of vaccination consists in inoculating a pathogen that has been rendered harmless into a healthy animal. This pathogen aims to stimulate the organism’s natural defenses (the immune system). This primary immunitary reaction triggers a memory that allows the organism to defend itself more effectively in the event of ensuing infection by the same pathogen. This reaction is impossible in shrimp due to their lack of immune memory.
Recent research has shown that shrimp and other decapods are nevertheless able to develop an immune response close to that of specific higher vertebrates. Yet, a large-scale application of these results would be premature.

How to compensate for the lack of acquired immunity in shrimp?

In aquaculture, both farming practices and environmental conditions subject shrimp to stressful situations that impact them strongly.These stressors (pollution, low level of oxygen, temperature variations, sorting and transfer, osmotic shock) can directly cause death or favor the development of opportunistic pathogens and mortal infections. As with all livestock species, the best way to reduce these impacts on farmed shrimp is by erecting a number of barriers so as to prevent the development of pathogens. In this respect, physical and sanitary barriers are the most effective means of prevention.
Given the lack of real specific immunity in shrimp, it is essential to resort as much as possible to the expression of their non-specific immunity.
Yet, a state of zero risk does not exist: aquaculture facilities are regularly contaminated by bacteria, viruses, or parasites. In this respect, certain substances with immunostimulatory effects can help prepare the shrimp’s body against the risk of disease outbreaks.The term "immunostimulant" generally encompasses all components that have demonstrated their ability to improve one or more measurable responses stemming from the shrimp’s nonspecific system. Immunostimulants aim to keep the immune system of shrimp alert by triggering a response from their non-specific immune system. In this respect, Βeta glucans and Manno-oligosaccharides (MOS) are particularly known to improve the resistance to bacterial and viral infections by activating the immune system and the function of phagocytic cells. Furthermore, antioxydants such as Vitamin C and Vitamin E can help increase stress resistance. Trace elements, such as selenium, also have anti-oxidant properties and can limit the effects of free radicals.
It is important to ensure that these immunostimulatory substances are provided in sufficient amounts through feed or directly in the context of rearing, especially during stressful or pivotal periods: sorting and transfer, osmotic shock, etc.

Would you like to find out more about stress management in shrimp and the available solutions to reduce its effects in farms? Thanks to its thorough knowledge of shrimp nutritional requirements, the TECHNA Group can provide you with support in conceiving and manufacturing your shrimp feed.
Please contact our experts!