Beneficial roles of feed additives as immunostimulants in aquaculture: a review

The use of antibiotics in the feeds of cultured aquatic animals to mitigate infectious diseases or to boost growth performance is commonly practised. In recent years, the prophylactic use of antibiotics has been criticized which eventually led to their ban in animal production by many countries. In view of the current restrictions on antibiotic use, there is a critical need to evaluate alternatives. One potential substitute for antibiotic growth promoters in aquafeeds is organic acids and/or their respective salts. The use of dietary organic acids in the culture of aquatic animals has been the focus of much research and commercial interest recently. This review provides a comprehensive compilation of the current knowledge on the use of organic acids in aquafeeds, with emphasis on its impacts on growth, nutrient utilization, mineral availability, gut microbiota and disease resistance. Many studies have reported that some organic acids can significantly enhance the growth performance and health status of fish. Contradictory results have also been reported, which seems to depend on the aquatic animal species, type and concentrations of organic acids and the culture conditions used. Recent research indicating the beneficial impact of dietary organic acids on shrimp growth and health is highlighted. Possible mechanisms of action of these functional feed additives are discussed. Strategies for enhancing the effectiveness of dietary organic acids are given. This review aims to contribute to the sustainability of global aquaculture production by providing a viable alternative to harmful antibiotics, thereby meeting the growing consumer demand for antibiotic-free seafood products.

The utilization and mode of action of organic acids in the feeds of cultured aquatic animals

Isolation of fucoidan from Sargassum polycystum brown algae: Structural characterization, in vitro antioxidant and anticancer activity.

A rapid and novel microwave-mediated protocol was established for extracellular synthesis of metallic silver (Ag) and zinc oxide (ZnO) nanoparticles using the extracts of macro-algae Gracilaria edulis (GE) and also examined its anticancer activity against human prostate cancer cell lines (PC3). The formation of silver nanoparticles (GEAgNPs) and zinc oxide nanoparticles (GEZnONPs) in the reaction mixture was determined by ultraviolet-visible spectroscopy. The synthesized Ag and ZnO nanoparticles were characterized by X-ray diffraction, Fourier transform infra-red spectroscopy, energy dispersive X-ray, and field emission scanning electron microscopy. The silver and zinc oxide nanoparticles were spherical and rod-shaped, respectively. Cell viability assays were carried out to determine the cytotoxic effects of AgNPs and ZnONPs against PC3 and normal African monkey kidney (VERO) cell line. The inhibitory concentration values were found to be 39.60, 28.55, 53.99 μg/mL and 68.49, 88.05, 71.98 μg/mL against PC3 cells and Vero cells for AgNPs, ZnONPs, and aqueous G. edulis extracts, respectively, at 48 h incubation period. As evidenced by acridine orange/ethidium bromide staining, the percentage of the apoptotic bodies was found to be 62 and 70 % for AgNPs and ZnONPs, respectively. The present results strongly suggest that the synthesized ZnONPs showed an effective anticancer activity against PC3 cell lines than AgNPs.

Microwave-Mediated Extracellular Synthesis of Metallic Silver and Zinc Oxide Nanoparticles Using Macro-Algae (Gracilaria edulis) Extracts and Its Anticancer Activity Against Human PC3 Cell Lines

Fucoidan is comprised of a fucose backbone with sulphate groups, whose variation is important to the functionality of the polysaccharide. The structure of fucoidan has been reported to vary according to species, season, location and maturity; however there is currently little published data to support this. Understanding the seasonal variation of fucoidan is important for industrial applications to identify optimum harvesting times and ensure consistent product composition. This study explores the seasonal variation of three species of brown macroalgae, Fucus serratus (FS), Fucus vesiculosus (FV) and Ascophyllum nodosum (AN), harvested monthly off the coast of Aberystwyth, UK. Average fucoidan content is 6.0, 9.8 and 8.0 wt% respectively for FS, FV and AN, with highest quantities extracted in autumn and lowest in spring. Fucose content, varied between 18 and 28, 26–39 and 35–46 wt% and sulphate content between 30 and 40, 9–35 and 6–22 wt% for FS, FV and AN respectively, with both fluctuating inversely to the total fucoidan content. Size exclusion chromatography (SEC) has provided insight into the structural differences between the species. Based on the molecular weight (MW) distribution, and in line with previous research, it is hypothesised that fucoidan in FS has a more complex structure, with a higher degree of associated sulphate ions than in FV and AN which have a simpler, linear structure with less associated sulphate ions.

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The seasonal variation of fucoidan within three species of brown macroalgae

The effect of fucoidan from brown seaweed Sargassum wightii on WSSV resistance and immune activity in shrimp Penaeus monodon (Fab)

Dietary effect of Sargassum wightii fucoidan to enhance growth, prophenoloxidase gene expression of Penaeus monodon and immune resistance to Vibrio parahaemolyticus

This study was carried out to determine the effect of seaweed polysaccharide, fucoidan from brown seaweed, Sargassum wightii, on Penaeus monodon postlarvae (PL) against white spot syndrome virus (WSSV). The fucoidan was extracted from S. wightii, and the yield was observed as 2.832 ± 0.204%. Artemia franciscana nauplii were enriched with extracted fucoidan at four different concentrations (100, 200, 300, and 400 mg/L) and fed to shrimp P. monodon PL for 20 d. After feeding experiment, the P. monodon PL were challenged with WSSV, and the mortality percentage was recorded daily up to 21 d. During the challenge test, the control PL showed 100% cumulative mortality within 9 d, but the fucoidan-enriched Artemia nauplii fed groups of PL exhibited 60–94% cumulative mortality within 21 d. The reduction in mortality percentage of experimental groups of PL over control PL was ranged between 33.71 and 61.65%. The polymerase chain reaction analysis confirmed the concentration-dependent variation in WSSV infection.

Antiviral Effect of Fucoidan Extracted from the Brown Seaweed, Sargassum wightii, on Shrimp Penaeus monodon Postlarvae against White Spot Syndrome Virus

The present study was carried out to determine the antibacterial effect of caprylic acid in the culture system of Artemia franciscana nauplii inoculated with shrimp pathogens Vibrio harveyi and V. parahaemolyticus. To begin with, the antibacterial effect of different concentrations (1, 10 and 100 mM) of caprylic acid against V. harveyi and V. parahaemolyticus was assessed through bacterial growth study. This indicated that at 100 mM concentration, the growth of the pathogens was completely inhibited within 5 h, whereas, in 1.0 and 10 mM concentrations, effective inhibition was observed with the extension of time. Subsequently, the influence of pH variation on the growth inhibitory effect of 10 mM caprylic acid against V. harveyi and V. parahaemolyticus at different pH (5–7) was also made through bacterial growth study. At pH 5, the pathogen growth was very less, compared with pH 6 and 7. The Artemia nauplii (instar II) reared in 10 mM caprylic acid supplemented medium were challenged with V. harveyi and V. parahaemolyticus, and the mortality was recorded at an interval of 6 h up to 60 h. In this study, the mortality of Artemia nauplii reduced to 20.61 and 16.30% in V. parahaemolyticus and V. harveyi challenged groups, respectively. The present results provide evidence for the potential antibacterial activity of caprylic acid in aquaculture against luminescent vibrios.

Antibacterial effect of medium-chain fatty acid: caprylic acid on gnotobiotic Artemia franciscana nauplii against shrimp pathogens Vibrio harveyi and V. parahaemolyticus

Enhancement of growth, innate immunity, and disease resistance by probiotic Enterococcus faecium MC-5 against Aeromonas hydrophila in Indian major carp Cirrhinus mrigala.

Madasamy Sivagnanavelmurugan

Papers

The effect of fucoidan from brown seaweed Sargassum wightii on WSSV resistance and immune activity in shrimp Penaeus monodon (Fab)

Dietary effect of Sargassum wightii fucoidan to enhance growth, prophenoloxidase gene expression of Penaeus monodon and immune resistance to Vibrio parahaemolyticus

Antiviral Effect of Fucoidan Extracted from the Brown Seaweed, Sargassum wightii, on Shrimp Penaeus monodon Postlarvae against White Spot Syndrome Virus

Antibacterial effect of medium-chain fatty acid: caprylic acid on gnotobiotic Artemia franciscana nauplii against shrimp pathogens Vibrio harveyi and V. parahaemolyticus

Enhancement of growth, innate immunity, and disease resistance by probiotic Enterococcus faecium MC-5 against Aeromonas hydrophila in Indian major carp Cirrhinus mrigala.