Natural plant extracts are widely used in research and production due to their rich resources, low cost, green source, small toxic and side effects to animals, and no harmful drug residues. At present, a large number of studies have shown that plant extracts contribute to the growth of animals. The body composition of fish is affected by the nutritional level of feed, breeding environment, fish species, age, sex and other factors, among which feed is the main factor affecting the body composition of the fish. The protein and fat content in fish is an important factor that reflects the quality of muscle nutrition (Wang ,2024). The high fat content in the feed will cause fat deposition in the liver, abdominal cavity, muscles and other tissues of the fish, affecting the health of the fish (Yang ,2024). Liver ratio and visceral ratio are important indicators reflecting the development of the liver and viscera of fish. Studies have shown that the content of lipids in feed has a significant impact on the viscerosomatic index and hepatopancreas somatic indices of fish (Wang ,2023). When fish consumes too much fat, its viscerosomatic index and hepatopancreas somatic indices will also increase (Mi ,et al,2024 ;Wei ,et al,2024 ;Zhao ,et al,2023). Previous studies of the author's team have shown that when the fat content of grouper exceeds 15%, it will cause liver fat deposition, leading to lipid metabolism disorders, liver damage, and a decline in growth rate, which will also lead to large-scale death (Li ,et al,2018 ;Zou ,et al,2021 ;Zou ,et al,2019). In this test, the viscerosomatic index of grouper fish in the high-fat group fed with high-fat diet was significantly higher than that of other groups, indicating that there was excess fat accumulated in the fish. Adding plant extracts can reduce fish body fat deposition and improve fish quality. The study found that the addition of wolfberry polysaccharides to the feed can significantly reduce the hepatopancreas somatic indices of spotted sea bass (Huang ,et al,2023). The intake of a high-fat diet (HFD) will reduce the muscle mass of aquatic animals, and sanguinarine(sanguinarine) can improve the muscle mass of Ctenopharyngodon Idella(Ctenopharyngodon Idella) by reducing fat deposition and increasing protein content (Shi ,et al,2024). Sun and other learners’ research have found that supplementing 1.12 or 1.18 g/kg Taurine(Taurine) in non-fish meal (NFM) diet can improve the fillet quality and muscle antioxidant capacity of grass carp (Sun ,et al,2024). The research results of this experiment are also consistent with it. After adding grapefruit polysaccharides to high-fat feed, the content of whole grouper fish fat and muscle coarse fat decreased significantly. At the same time, the content of fat droplets was observed by liver oil red O staining. It was found that after adding grapefruit polysaccharides, the content of fat droplets in the high-fat group was significantly reduced, indicating that grapefruit polysaccharides can reduce fat deposition.
The texture characteristics of groupers are affected by many factors, including fish type, growth environment, feed composition, feeding management, growth stage, processing process, preservation and treatment methods, etc. (Wang ,et al,2024). The texture characteristics of fish are generally shown in terms of hardness, adhesion, cohesion, elasticity, adhesiveness and chewiness (Xu ,et al,2022). Usually, if the fish becomes more solid and more elastic, the taste will be better (Wu ,et al,2021). In this experiment, adding grapefruit polysaccharides to high-fat feed can improve muscle elasticity, indicating that grapefruit polysaccharides can improve the taste of fish.
The liver is the center of fish energy metabolism and also an important organ for excretion. When the liver of fish is damaged, hepatocytes will cause vacuolation, nuclear pyknosis offset, fat precipitation and other phenomena (Rhind ,et al,2011). In the pathophysiological process of the liver, the oxygen free radicals produced by lipid peroxidation and biological oxidation are considered to be an important cause of liver damage, while malondialdehyde (MDA) is a lipid peroxidation product of the liver, which can reflect the degree of liver damage. Superoxide dismutase (SOD) can remove superoxide anion free radicals, reflecting the body's ability to remove free radicals (Zhang ,et al,2023). Su Yongteng's research shows that rhubarb anthraquinone extract can significantly improve SOD vitality and reduce MDA content, indicating that rhubarb anthraquinone extract can remove free radicals in the body, improve the body's antioxidant function to a certain extent, and protect the liver from damage (Yang ,et al,2023). Yuan eta. (Yuan ,et al,2018) Studies have shown that SCAP can relieve liver damage caused by ethanol in mice, reduce MDA levels and increase SOD activity. In this experiment, it was observed that the liver tissue of grouper fish fed with high-fat feed was seriously damaged. After adding grapefruit polysaccharide, the phenomenon of hepatocyte vacuolation was reduced, the cell morphology returned to normal, the MDA content of liver tissue decreased significantly, and the SOD activity increased significantly, indicating that grapefruit polysaccharide can effectively remove the harm of free radicals, protect cells from damage and improve the liver health of groupers.
Plant polysaccharides also show immune regulatory activity (Liu ,et al,2011; Güroy ,et al,2022). The study found that polysaccharides extracted from Auricularia heimuer(Auricularia heimuer) can significantly inhibit the secretion of NO, TNF-α and IL-6 (Jen ,et al,2021). Ginger polysaccharide can promote myeloid-derived suppressor cell apoptosis by regulating lipid metabolism (Song ,et al,2023). After adding grapefruit polysaccharides in this test, the expression levels of IL-1β and IL-8 in the TDF2 group were significantly lower than that of the high-fat group. This shows that the addition of grapefruit polysaccharides to the feed has an anti-inflammatory effect, which helps to reduce the inflammatory reaction thus reduce the damage caused by excessive inflammation. The expression level of apoptosis-related genes caspase3 and caspase8 decreased significantly in the TDF2 group, indicating that grapefruit polysaccharide can inhibit the apoptosis process in groupers.
Conclusion
In summary, this test confirms that the addition of grapefruit polysaccharides to the feed can improve the quality of the fish body, reduce the fat content of the liver, muscles and whole fish, reduce the deposition of fat in the fish body, promote the immune function of grouper, and protect the liver from damage. The test results provide reference for plant extracts as feed additives to reduce fish fat deposition and improve seawater fish health.