In Southeast Asian nations, cultured hybrid groupers are facing serious infestation by the marine parasitic leech Zeylanicobdella arugamensis (Annelida, Hirudinea). They attach to the hybrid groupers by sucking and biting on the surface of the skin, paving the way for secondary infection upon the fish. The objective of the study is to utilize the locally available seaweed to control the infestation of parasitic leeches. The methanol extracts of the brown alga Sargassum polycystum C. Agardh, 1824 (Phaeophyceae) from Sabah were prepared and investigated for antiparasitic efficacy against Z. arugamensis through in vitro bioassay. A total of 126 adult leeches from the host hybrid groupers were obtained from the fish hatchery. The parasitic leeches were treated with the methanol extracts of S. polycystum for 180 min by preparing five different dosages at concentrations of 100, 50, 25, 12.5, and 6.25 mg/mL. The brown alga was found to have high antiparasitic efficacy, resulting in 100% leech mortality over a short period of time. It showed the highest antiparasitic efficacy (total mortality of leeches) in a short time limit of 0.96 ± 0.44 min, for 100 mg/mL of the extract. Observations on leech behavior in the positive control and the seaweed extract treatments showed vigorous swimming before mortality. LC-MS/MS analysis was used to reveal the phytochemical composition of the extract to understand the nature of the main components responsible for its antiparasitic activities. A total of 29 metabolites were identified via Q Exactive HF Orbitrap mass spectrometry, including two flavonoids (ephedrannin A and hinokiflavone), two organoarsenics (1-dimethylarsinoyl-heptadecane and cacodylic acid), four heterocyclic compounds, and two chlorophyll breakdown products. The presence of bioactive compounds could increase the mortality rate of parasitic leeches. Thus, this study concludes that the brown alga showed high efficacy in its antiparasitic activities and can be effectively applied for treatment in grouper aquaculture farms for sustainable aquaculture.

The increased development of aquaculture has resulted in increased demand for high-protein aquafeed. An increased demand for high-protein aquafeed means an increase in exploitation of unsustainable protein sources such as fishmeal for aquafeed production. Thus, alternative protein sources such as fermented macroalgae is explored. Fermented macroalgae had been tested as aquaculture diets in some studies, but with limited coverage in relation to aquaculture. Therefore, this review provides a new perspective regarding their nutritional qualities as aquaculture diets, and their impacts on growth performances of aquaculture animals.

The gastrointestinal (GI) microbiota is a group of complex and dynamic microorganisms present in the GI tract of an organism that live in symbiosis with the host and benefit the host with various biological functions. The communities of GI microbiota are formed by various aerobic, anaerobic, and facultatively anaerobic bacteria in aquatic species. In spiny lobsters, common GI microorganisms found in the GI tract are Vibrio, Pseudomonas, Bacillus, Micrococcus, and Flavobacterium, where the structure and abundance of these microbes are varied depending on the environment. GI microbiotas hold an important role and significantly affect the overall condition of spiny lobsters, such as secreting digestive enzymes (lipase, protease, and cellulase), helping in digesting food intake, providing nutrition and synthesising vitamins needed by the host system, and protecting the host against infection from pathogens and diseases by activating an immune mechanism in the GI tract. The microorganisms in the water column, sediment, and diet are primarily responsible for altering, manipulating, and shaping GI microbial structures and communities. This review also highlights the possibilities of isolating the indigenous GI microbiota as a potential probiotic strain and introducing it to spiny lobster juveniles and larvae for better health management.

Vibriosis and parasitic leech infestations cause the death of various farmed fish, such as groupers, hybrid groupers, sea bass, etc., in Malaysia and other Southeast Asian countries. In the absence of natural control agents, aquaculture operators rely on toxic chemicals to control Vibrio infections and parasitic leeches, which can have a negative impact on the environment and health. In the present study, we investigated the antivibrio and antiparasitic activities of the aqueous extract of giant sword fern (GSF) (Nephrolepis biserrata, Nephrolepidaceae, locally known as “Paku Pedang”) against four Vibrio spp. and the parasitic leech Zeylanicobdella arugamensis, as well as its metabolic composition using the ultra-high-performance liquid chromatography–high-resolution mass spectrometry system (UHPLC-HRMS). The data show that the aqueous extract of GSF at a concentration of 100 mg/mL exhibits potent bactericidal activity against V. parahaemolyticus with a zone of inhibition of 19.5 mm. In addition, the extract showed dose-dependent activity against leeches, resulting in the complete killing of the parasitic leeches within a short period of 11–43 min when tested at concentrations ranging from 100 to 25 mg/mL. The UHPLC-HRMS analysis detected 118 metabolites in the aqueous extract of GSF. Flavonoids were the primary metabolites, followed by phenolic, aromatic, fatty acyl, terpenoid, vitamin and steroidal compounds. Notably, several of these metabolites possess antibacterial and antiparasitic properties, including cinnamaldehyde, cinnamic acid, apigenin, quercetin, cynaroside, luteolin, naringenin, wogonin, 6-gingerol, nicotinamide, abscisic acid, daidzein, salvianolic acid B, etc. Overall, our study shows the significant antibacterial and antiparasitic potential of the GSF aqueous extract, which demonstrates the presence of valuable secondary metabolites. Consequently, the aqueous extract is a promising natural alternative for the effective control of Vibrio infections and the treatment of parasitic leeches in aquaculture systems.

Modern technology has been evolving towards nanotechnology due to the materials that can be transformed and manipulated on micro and nanoscales. In terms of detection, nanomaterials offer substantial sensing advantages, particularly in terms of enhanced sensitivity, synergistic effect, stability and selectivity. The immobilization of nanoparticles could alter the physicochemical properties of the electrode’s surface depending on the type of materials synthesized and employed. This research examined the synthesis of multiwalled carbon nanotubes (MWCNTs) and chitosan (CS), as well as the immobilization of Prussian blue (PB) on the surface of a bare gold electrode (AuE). These materials have been reported to have strong electrical conductivity and nanomaterial compatibility. In contrast, aluminum has been described as a replacement for traditional water quality treatment processes, such as chlorination and ozonation. Aluminum concentrations must be monitored despite the use of chemical treatment for water quality. Hence, excessive levels of exposure frequently result in neurotoxic effects including Alzheimer’s and Parkinson’s disorders. In this experiment, the optimal conditions for f-MWCNTs, CS, PB, and AuE for the detection of Al³⁺ are phosphate-buffered saline (PBS) (0.1 M, pH 2) with 5 mM Prussian Blue; scan rate = 0.25 Vs⁻¹; accumulation duration = 25 s; and volume = 10 mL (ratio of 4:6). The performance of f-MWCNTs, CS, PB, and AuE was measured between 0.2 and 1 ppm with a correlation coefficient of R² = 0.9853 (y = 0.0387x + 0.0748). The limit of detection (LOD) of the modified electrode was determined to be 0.002 ppm, with a recovery of 98.66–99.56%. The application of nanoparticles resulted in various advantages, including high conductivity, a simple, less time-consuming preparation technique, and enhanced sensitivity and stability for detecting the lowest concentration of Al³⁺ in drinking water.