26 MARCH 2025 • WORLD AQUACULTURE • WWW.WAS.ORG is not without risk and might eventually become much more expensive, if (when) technical quality rock bottoms. From above it becomes evident that somewhere in this triad of compromises between nutritional fish requirements, LCF considerations and producing pellets with high technical integrity, lies the competitive edge in sustainable aquaculture. Enhancing Raw Material Flexibility with Advanced Extruder Design Extrusion technology plays a pivotal role in the manufacturing of aquaculture feeds. The raw materials are pasteurized, cooked, shaped and expanded into the wellknown cylindrically shaped feed pellets. The ability to achieve good quality based on upstream choices (raw materials, processing conditions, grinding and mixing) can be termed as the ‘processing window.’ Sometimes this will be wide to allow for several combinations of raw materials and processing conditions, while at other times it could become very narrow. For the reasons discussed above, the extrusion platform that effectively expands the processing window to allow for raw material flexibility — minimizing formulation constraints while delivering acceptable technical quality — will undoubtedly prove to be the most cost-effective production solution in the long term. Traditional single-screw (SX) and twin-screw (TX) extruders have long been employed. Each offers unique benefits while presenting distinct limitations. Recent innovation in twin-screw extrusion (‘AFX’) is specifically targeted to aquatic feeds. It employs fundamentally different screw elements that are more resilient to wear and that modify the energy transfer dynamics within the extruder barrel. This study aims to assess and justify the claims regarding the enhanced performance and processing flexibility of the AFX system compared to traditional TX and SX technologies. Farmed fish have in recent years consolidated a position as one of the most sustainable sources of dietary protein, thanks to their exceptional feed conversion ratios (FCR) compared to terrestrial livestock (Tacon and Metian, 2015). With the rising global demand for high-quality protein and increased emphasis on effective water management policies, aquaculture is confronted with both significant challenges and promising opportunities for sustainable growth (FAO, 2020). As the industry develops, managing production costs — particularly feed formulations and raw materials — remains a critical challenge. The Aquafeed Triad The end game in aquaculture is about promoting fish growth, health and survival at the least possible expense. Feed cost is a large part of the expense, whilst fish growth, -health and -survival entail effects from feed nutritional composition as well as technical feed quality. Technical feed quality involves all the attributes of the feed that effectively allow transport of nutrients to — and uptake in — the fish. Factors include physical qualities like durability, fat retention properties, size uniformity, density/buoyancy and hardness as well as physicochemical factors such as water activity and oxidative stability (Thomas & van der Poel, 1996). In aquafeed manufacturing, raw material and formulation costs make up a substantial part of the operating expenses. Sometimes costs can be further challenged if constraints are put onto the formulations, driven by production to be able to deliver on quality. Examples could include a minimum starch inclusion, a maximum inclusion of soy, beans or another ingredient or — for high fat feeds — a minimum inclusion of hardened oils (which is an expensive component that promotes fat retention but can reduce fish growth). It can be very expensive to specify how the nutrients are put together, straying away from a least cost formulation (LCF) optimum. On the other hand, producing feeds solely considering a LCF perspective Advancements in Twin Screw Technology for Aquafeed Production: A Comparative Study Anders Haubjerg PHOTO 1. Single- or twin-screw extrusion processes utilized for decades to cook, pasteurize, shape and expand raw materials into homogenous aquatic feed pellets. PHOTO 2. A few of the historical steps in extrusion development for the past 75 years.
RkJQdWJsaXNoZXIy MjExNDY=