Trial results show herb’s potential to improve shrimp growth and survival, but assessing the appropriate dose is important
The susceptibility of farmed shrimp, such as the Pacific white shrimp (Litopenaeus vannamei), to the pathogenic marine bacterium Vibrio alginolyticus may be heightened when the water quality is suboptimal, resulting in high mortality and considerable economic losses to shrimp farmers. In order to support the health of shrimp during the grow-out period, shrimp farmers are utilising a variety of dietary immunostimulants. Herbal immunostimulants represent a promising alternative, not only because their antimicrobial properties are cost-effective and eco-friendly, with negligible side effects, but also because they can improve the animal’s growth performance.
Moringa, or drumstick tree (Moringa oleifera), is a fast-growing, drought-resistant plant native to the Indian subcontinent and is widely known for its nutritional value. Moringa is a rich source of dietary fibres, proteins, vitamins, minerals and lipids. Additionally, it possesses a multitude of beneficial pharmacological properties, including anticancer, antidiabetic, anti-inflammatory, antioxidant, antifungal and antibacterial properties. These properties are attributed to the presence of bioactive compounds, including phenolic acid and flavonoids.
A number of studies on aquatic animals, including giant freshwater prawns, Pacific white shrimp, Nile tilapia, grass carp and common carp, rainbow trout and others, have indicated that the incorporation of extracts of moringa leaves into the animals’ diets could result in improvements in their growth and physiology, as well as the upregulation of immune-related gene functions. Nevertheless, moringa is also known to possess certain concentration-dependent toxicological properties, which can be determined through a dose-response relationship. Some studies have investigated the effect of moringa extracts on fish and shrimp. However, there is an inadequate body of research on the effect of moringa extracts in diets as in vitro and in vivo immunostimulants for Pacific white shrimp.
This article has been adapted and summarised from the original publication [Abidin, Z. et al. 2022]. The aqueous extract of Moringa oleifera leaves has been demonstrated to enhance nonspecific immune responses, resistance against Vibrio alginolyticus, and growth in whiteleg shrimp (Penaeus vannamei). [42] Animals 2022, 12(1) The study presents the results of an investigation into the effect of the moringa leaves’ water extract on several immune responses, growth and resistance of L. vannamei against V. alginolyticus.
Study setup
The shrimp utilised in this study were sourced from the Aquatic Animal Centre, National Taiwan Ocean University (NTOU), Taiwan. The shrimp were acclimated to laboratory conditions at a temperature of 28 degrees Celsius ± 1 degree Celsius and a salinity of 32 ± 1 practical salinity units (psu) for a period of two weeks. During the acclimation period, the shrimp were fed a commercial diet three times a day. Only shrimp that exhibited healthy characteristics, including no signs of disease, normal feeding behavior, and a hard carapace, were selected for use in the experimental treatments.
The leaves of the moringa plant, which is commercially available in a dry state, were obtained from the organization Rumah Kelor, which is based in Blora, Indonesia. The dried leaves were then milled into a fine powder and mixed with hot distilled water at a ratio of 1:9. The mixture was subsequently left for 24 hours at room temperature. The resulting solution was filtered to separate the solids, and the liquid was subsequently dried in a freeze dryer for three days to yield extract powder. The recovery rate of the dry leaves was 13.1%, and the powder extract was stored at minus 20 degrees Celsius until further use.
For detailed information on the experimental design, animal husbandry, moringa extraction and diet preparation; in vitro study of viability and immune response; in vivo study of the immune response; immune-related gene expression; shrimp growth performance; challenge with V. alginolyticus; and statistical analyses, please refer to the original publication.
Results and discussion
The results of the in vitro assessment of viability and immune response demonstrated that there was no significant difference in the viability of hemocytes (cells found in the hemolymph, or blood, of shrimp and involved in the animal’s immune response) when treated with 25–250 ppm of the moringa leaf extract in comparison to controls. When hemocytes were treated with 500–2,000 ppm of the moringa extract, their viability was found to decrease. However, the viability was found to be over 80 percent for all treatment concentrations evaluated.
The results demonstrated that the viability of the hemocytes treated with up to 250 ppm of the moringa extract was comparable to that of the control group. However, a tendency towards decreased viability was observed in hemocytes treated with a dosage exceeding 250 ppm. Consequently, the moringa extract is deemed to be safe for hemocytes at a low dosage of up to 250 ppm. However, toxicity assessment will continue to be a crucial aspect. In vitro studies, such as the present one, represent a cost-effective alternative to the selection of new immunostimulant candidates for aquaculture. This is because they may yield more repetitive results under a highly controlled experimental environment.
With regard to the growth performance of shrimp, the results of the 60-day rearing period indicated that the shrimp fed diets containing the moringa extract exhibited a higher growth rate than the control shrimp. The ME2.5 group exhibited a notable increase in weight, specific growth rate, and a reduction in feed conversion rate (FCR) in comparison to the control diet. However, this was not significantly different from the ME1.25 and ME5.0 groups. There was no significant difference in survival rate among the treatment groups.
The presence of antinutrients in moringa can significantly impede the absorption of nutrients in the diet. A high concentration of moringa extract in the diet may inhibit digestive enzymes and complex dietary proteins due to the presence of tannins, saponins and other secondary metabolites, which do not provide nutrition when present in excess. Nevertheless, when present in appropriate quantities, the incorporation of herb extracts into the diets of aquatic animals has been observed to stimulate the secretion of digestive enzymes and function as an appetiser, thus improving growth and diet utilisation.
The results of the challenge test demonstrated that the unchallenged control group exhibited a 100% survival rate, whereas the survival rate of the other treatment groups exhibited a significant decline from six to 48 hours following the injection of V. alginolyticus. The survival rates of the shrimp in the challenged treatments ranged from 43.3 to 50 percent. One day of diet administration had no effect on the survival rate of all the treatment groups. Following a two-day period of diet administration, the survival rate of the ME5.0 group was found to be significantly higher than that of the control group. After four days of diet administration, the survival rate of the ME2.5 and ME5.0 groups was found to be higher than that of the control group. After seven and 14 days of diet administration, the survival rates of the ME5.0 and ME2.5 groups were found to be significantly higher than that of the control group. Overall, 72 hours after the bacterial injection, the survival rate was significantly higher in the ME2.5 group fed the treatment diet for four and seven days (73.3 percent) compared to the control group, followed by the ME5.0 group fed the treatment diet for seven days (66.7 percent).
Perspectives
The results demonstrated that dietary supplementation with moringa at a dose of 2.5 grams per kilogram resulted in the most favourable improvement of various non-specific immune responses and growth performance in L. vannamei shrimp. Furthermore, the administration of a diet containing moringa leaf extract at this dose for four and seven days was found to be effective against V. alginolyticus infection.