Ragworms can utilise Chitosan-treated aquaculture wastewater, enabling sustainable recycling and production of aquafeed ingredients
Creators: name: Mackie, Blair Alexander
Publisher: name: The University of Edinburgh
Year: 2024
Subjects: ragworms
wastewater treatment
chitosan
water pollution
sustainability
aquaculture
fish food

description: Aquaculture facilities are highly dependent on sources of high-quality ingredients from conventional capture fisheries (fish meal and fish oil), which have stagnated in production in recent decades. In addition, wastewater from aquaculture facilities requires specific treatment and disposal. Both issues are possibly limiting the potential of the aquaculture industry. An approach to increase resource efficiency in aquaculture is to utilise nutrientdense wastewater from aquaculture to grow biomass that could be returned to and applied in aquaculture systems as high-quality ingredients by inclusion in aquafeeds. It has been shown in previous research that ragworms (Hediste diversicolor) can recycle nutrients found in aquaculture wastewater with good growth rates, as well as favourable nutritional profiles that are suitable for many species of marine animals that are typically reared in aquaculture systems. However, the aquaculture wastewater must be treated in some way before it can be fed to ragworms as they cannot be cultured in the wastewater directly. One way to do this that has not been investigated before is by coagulating and flocculating the aquaculture wastewater using chitosan before feeding it to ragworms. Chitosan is a natural biopolymer derived from chitin, which is a major component of the exoskeletons of crustaceans and insects. Chitosan is generally accepted as non-toxic and has many other benefits over metal-based coagulants (e.g., alum) including biodegradability and environmental friendliness. Therefore, the objective of this thesis was to investigate technical aspects related to utilising ragworms to recycle nutrients contained in aquaculture wastewater that have been coagulated and flocculated by chitosan. To do this, growth rates, mortality rates and the nutritional suitability of ragworms as a feed resource for fish species reared in aquaculture after being fed chitosan coagulated and flocculated aquaculture wastewater were assessed. A series of cultivation experiments were carried out on juvenile ragworms in the laboratory. The results indicated that ragworms can successfully be cultivated on aquaculture wastewater that has been coagulated and flocculated by chitosan. In addition, the ragworms had nutritional compositions (amino acid and fatty acid profiles) that met the requirements for a variety of fish species. However, it was determined that a high concentration of chitosan v in aquaculture wastewater can have detrimental effects on ragworms when it is fed to them. Furthermore, aquaculture wastewater can contain toxic contaminants, such as heavy metals, which chitosan was demonstrated to decrease ragworm exposure to toxic aluminium when feeding. Ultimately, it was demonstrated that ragworms can efficiently utilise and incorporate nutrients contained within chitosan-coagulated and flocculated aquaculture wastewater to produce aquafeed that is high in protein and contains essential fatty acids and amino acids.