The seafood industry has been rapidly moving toward high-intensity aquaculture to prevent the exploitation of wild stocks and address ever-growing demands. However, disease outbreak is an inevitable outcome of intense aquaculture. Farmers attempts to control diseases using antimicrobial drugs which is the main cause for concerns about development of drug-resistant organisms. Probiotics and natural immunostimulants are alternatives to combat disease occurrence in a more sustainable aquaculture practice. However, application of these beneficial bioactives are complicated due to ineffective delivery methods such as immersion and injection. These methods are often inefficient due to lack of control over the stability and dosage of delivered bioactives and possible environmental contamination.
This study used encapsulation techniques to develop a controlled release system for delivery of probiotics and nutrients to black-footed abalone (Haliotis iris). A multi-layer bead structure was developed to immobilise three probiotic bacteria (Vibrio sp., Exiguobacterium sp. and Enterococcus sp.). The release of the encapsulated probiotics in seawater was measured using a fluorescence microscope. A feeding trial was performed to assess the effect of the encapsulated probiotic food on growth and health of juvenile abalone. Health parameters including reactive oxygen species (ROS) and viability of hemocytes were measured using flowcytometry. A metabolite profiling study of abalone foot muscle was carried out using gas chromatography-mass spectrometry (GC-MS).
The probiotics were successfully encapsulated in the developed beads with the encapsulation efficiency of 50-90%. The encapsulated probiotic beads showed high stability in seawater with less than 1% matrix erosion after 72 hr. Additionally, low bacterial release in seawater and high probiotic bacterial load (108 CFU) within the GIT of abalone demonstrated the successful delivery of viable probiotic bacteria to abalone using the developed beads. An improved growth performance observed in abalone fed with the encapsulated probiotic food compared to control animals. Flowcytometric analysis revealed lower level of ROS and high hemocyte viability (> 90%) which indicate better health parameters in encapsulated-probiotic fed abalone. Metabolomics study revealed significant variations in the profile of organic acids in encapsulated-fed abalone compared to control animals. In conclusion, this study demonstrated that encapsulation techniques can be used to design efficient carriers for delivering bioactives in aquaculture to enhance the production in a sustainable manner.