Scientists from Mansoura University in Egypt report that APS was associated with a specific growth rate that was 0.2% greater per day, and the fish gained an average of 9 grams more body weight after six weeks of feeding, compared to the control group.
A better feed conversion ratio was also reported by the researchers, led by Eman Zahran from the university’s Department of Internal Medicine, Infections and Fish Diseases.
In addition, increases in several immune measures variables were also recorded, according to findings published in the journal Fish & Shellfish Immunology.
“Herbal dietary supplementation can improve the fish health and thereby reducing the management expenses,” wrote the researchers. “APS is one of the important herbal plants that can be used as an alternative to antibiotics or as a fish vaccine adjuvant in order to develop a new strategy in fish immune-modulation; contributes to the enhancement of fish welfare and economic growth for sustainable aquaculture.
“Based on our findings, it can be concluded that APS dietary supplementation has a potential immune-modulatory and growth promoting effect in Nile tilapia.”
Tilapia is the third most important fish in aquaculture after carp and salmon in dollar value, according to the FAO: In 2011 3,957,949 tonnes of tilapia were produced in aquaculture globally, worth an estimated $6.7 billion. In comparison, 25,157,502 tonnes of carp (worth $36 billion) and 2,773,639 tonnes of salmon (worth $15.2 billion) were produced.
As can be seen from the figure below, China is the leading producer of tilapia, according to FAO data. Nile Tilapia (Oreochromis niloticus) is the leading species.
The Egyptian researchers investigated the effects of supplementing the diet of Nile tilapia with APS, a commercial product purchased from the El-Ahmadeya company, Egypt.
Sixty fish were divided into two groups: One group received only the basal diet, while the second group received the basal diet with APS at a level of 1500 mg per kg of diet for six weeks.
Results showed that APS was associated with significant increases in growth parameters, including weight, weight gain, feed intake, feed conversion ratio, and specific growth rate, compared with the control group.
In addition, APS supplementation was associated with an upregulation of phagocytic activity, bactericidal activity, and activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), and amylase.
“Our results are in agreement with previous investigations on juvenile yellow catfish (Pelteobagrus fulvidraco), Pacific white shrimp (Litopenaeus vannamei), and sea cucumber, which demonstrated the ability of the APS and Chinese herbal mixture; including Astragali supplementation, to improve the growth performance,” wrote the researchers.
“This could be attributed to many factors, either to the APS immunostimulating effect, thus reducing the bacterial and viral infections or its direct bactericidal effects on pathogenic gut microflora.
“Furthermore, we have found that APS supplementation increased the level of the amylase enzyme that could be correlated in part to its growth promoting effect. Such increase can result in digestibility improvement and availability of nutrients from feed stuffs.”
Source: Fish & Shellfish Immunology
Volume 38, Issue 1, May 2014, Pages 149–157, doi: 10.1016/j.fsi.2014.03.002
“Effects of dietary Astragalus polysaccharides (APS) on growth performance, immunological parameters, digestive enzymes, and intestinal morphology of Nile tilapia (Oreochromis niloticus)”
Authors: E. Zahran, E. Risha, F. Abdelhamid, H.A. Mahgoub, T. Ibrahim