by Yechiam Shapira, Senior Researcher, Phibro Animal Health, Isnreal
Over the last decade, we have seen a significant growth of the global shrimp industry. Total imports in 2022 were 3,248,338 tonnes (Van der Pijl, 2023), with additional production in China estimated at 1,487,501 tonnes (Fu-Chi, 2023). China and Vietnam (total 945,791 ton) and the US (837,622 tons) absorbed most of the growth in shrimp production. Ecuador has seen a compound annual growth rate (CAGR) of 17 percent from 2012 to 2019 and a very significant CAGR of 25 percent from 2020 to Q2 2023 (Villarrea, 2023).
Today, shrimp production is challenged by several problems that affects its’ growth worldwide. A Global Seafood Alliance 2022 survey that was presented to industry stakeholders mentions the most relevant challenges as: feed cost, market prices, diseases, and broodstock quality (Nikolik, 2022). Therefore, understanding the main environmental, nutritional, and operational factors that affect shrimp health may support the global efforts for promoting sustainable shrimp aquaculture.
Among the challenges mentioned above, shrimp health has the dramatic effect on the global industry. Asche (2021) evaluated the impact of disease outbreaks on the shrimp industry and concluding that the presence of disease increases the breakeven price significantly, and thereby increases the probability of losing money as well as increasing the risk.
To meet the growing consumption demands of the future, the focus on shrimp health is increasing, and more specifically how optimizing the functions of the gut can produce a more healthy, robust and profitable shrimp.
What is a healthy gut?
The shrimp digestive tract, and the digestive tract of that of all Crustacea, is made up of three sections (Holt, 2021). The foregut, containing the oesophagus and the two chambered stomach; the midgut; which begins at the junction of the hepatopancreas and traverses the length of the cephalothorax and the majority of the abdomen; and finally; the hindgut, containing the rectum and anus. These regions of the gut differ in their cell structure and function (Ceccaldi, 1989).
For shrimp, a healthy gut comprises various elements which include a robust intestinal structure and morphology, and efficient production of digestive enzymes. This allows optimal digestion and absorption of important nutrients. Also, an active non-specific immune response will promote the ability to eliminate invading pathogens such as viruses, bacteria and fungi, improving survival rates and productivity. A balanced intestinal microbiota can support the shrimps’ ability to survive, grow, and develop.
The benefits of a healthy gut in shrimp aquaculture:
1) Digestion and absorption of nutrients
The digestive tract is responsible, for many animals, and crustaceans in particular, for the nutritional function (Ceccaldi, 1989). This function includes ingestion, transit of nutrients, mechanical digestion, chemical and biochemical hydrolysis, cellular absorption, and transfer of excreta in the digestion tract. The lumen of the digestive tract is considered to be exposed to the external environment. The lateral wall of shrimp digestion tract is covered, in its fore and hind parts, with complexes of chitin and proteins which are removed at each molt with the exoskeleton. Another original aspect of the shrimp digestive tract relies on the fact that most reserves of the animal are accumulated here, and they are utilised at each inter-molting cycle. Optimal digestion and absorption of nutrients can lead to improved Feed Conversion Ratio (FCR), yield and better growth performance.
2) A balanced immune response
The shrimp non-specific immune system employs several hemolymph-borne factors in its fight against infection (Sis, 1992). Most of these factors are inducible, although they have no specific activity or memory. These factors serve to immobilise and agglutinate invaders as well as to sensitise them to phagocytosis. Both hemagglutinins and bactericidins have been identified in shrimp hemolymph. The agglutinins are protein molecules which play a role similar to that of antibodies. They also serve as opsonins and display some degree of binding specificity. Studies have also identified lectins involved in the immune response. These inducible hemolymph components are absorbed onto the surface of gram-negative bacteria where they enhance phagocytosis and the production of bacteriolysins and agglutinins. The carbohydrate receptors to which they bind are common ones, explaining their nonspecific response. Optimising the non-specific immune response in shrimp can reduce the impact of disease challenges and ultimately improve survival rates, and therefore, production yield.
Gut health can influence shrimp immunity
A function of gut epithelial cells is to act as a physical barrier against pathogens, and a healthy gut is composed of epithelial cells that are tightly joined together to form a protective layer.
A healthy gut microbiome plays a crucial role in shrimp immunity by competing with pathogenic bacteria for space and nutrients, producing antimicrobial compounds, and modulating the immune system mainly by stimulating the production of antimicrobial peptides, enhancing phagocytosis, and regulating inflammatory responses.
The gut-associated lymphoid tissue (GALT) contains immune cells, such as lymphocytes and macrophages, which are responsible for detecting and eliminating pathogens.
The gut plays a multifaceted role in shrimp immunity, encompassing physical, microbial, and immunological aspects. Maintaining gut health through proper nutrition, environmental management, and disease prevention strategies is essential for promoting shrimp health and productivity.
The role of functional feeds in optimizing the gut health of shrimp
In response to the global increase of intensive shrimp farming, the shrimp feed industry has been developed using several strategies (Mansour, 2022). Among these strategies, feed additive supplementation is one of the most important industries that has gained great importance for several shrimp species as growth promoters, immunity enhancers, and an alternative strategy for fighting disease (Sharawy, 2022). Common feed additives are astaxanthins (Goulin, 2024), β-glucans (Huifeng, 2019), organic acids (Wangquan, 2017), probiotics (Bacillus subtilis) (Zokaeifar, 2012) and many other natural herbs like rosemary, oregano and essential oils.
Among the natural feed additives, saponins are one of the major groups that are used in the last decades of shrimp culture. Saponins, widely found in plants, contain either a steroid or triterpenoid aglycone to which one or more sugar chains are attached (Oda, 2003). In addition, saponins have the potential to act as prebiotics by influencing gut microbiota and promoting the growth of beneficial bacteria (Hierro, 2008).
Saponins as beneficial additives
Saponins from the Quillaja saponaria tree and Yucca schidigera plant have been shown to have immunomodulatory, anti-inflammatory and antioxidant properties and may help to modulate the intestinal microflora. In addition, these specific saponins can increase cell membrane permeability, activate digestive enzymes and improve protein retention. Bo-Kun (2008) showed that Pacific White Shrimp (Liptopanaeus vannamei) that had been immersed in seawater containing 0.5 mg/l saponin showed increased resistance against Vibrio alginolyticus with a concomitant increase in phagocytic activity and clearance efficiency to V. alginolyticus. Martínez -Cordova (1998) evaluated the effects of Pacific white shrimp fattening rations containing Yucca schidigera extract, concluding that the additive has a positive effect in the quality of the water as well as in the production of the shrimp.
In addition, Hernandez-Acosta (2016) tested the inclusion of Yucca schidigera and Quillaja saponaria extracts in juvenile shrimp (L. vannamei) feeding with up to 2.0 g of saponins per kg of feed. The final average body weight and feed conversion ratio from shrimp feeding with 1.0 and 2.0 g of saponins per kg of feed had a significant improvement compared to other treatments.
PAQ-ProtexTM –a natural feed additive
Sourced from specific species of Quillaja saponaria trees and Yucca schidigera plants, PAQ-Protex is a hundred percent natural nutritional specialty product, a proprietary blend of triterpenoid and steroid saponins and polyphenols, also known as flavonoids. However, not all saponins are the same. The saponins and polyphenols in PAQ-Protex have been shown to produce meaningful changes in the digestive tract, supporting optimal gut health and immune function in shrimp and fish.
Increasing the gut surface area and activating digestive enzymes such as lipase and protease can lead to increased nutrient absorption, feed efficiency and production yield. Moving to intensive shrimp cultivation requires optimal design of the culture system: origin of the post larvae’s, biosecurity, water quality, operations, feeding, feed quality and functional feed additives. The challenge for the shrimp in these intensive conditions is to maintain optimal health status through good gut health. By adding PAQ-Protex, these goals can be achieved – improving the guts’ ability to function in the digestive track, and in addition, supporting immunity to maintain a good health status.
Published in the April 2024 issue of International Aquafeed.
