I would like to add a few more comments regarding making sinking vs floating fish feed.
1. Floating or sinking pellets are dependent on the formulation. Both the type of starch and inclusion rate of starch will make a shaped fish feed float. Generally, sinking pellets incorporate less starch and higher fat, with post-fat application likely.
2. Additionally, the type of die plate used will help with expansion (for floating) and gelatinization (binding) of the fish feed. For floating fish feed, a longer land length can assist with more expansion, hence, floating characteristics of the pellet. Alternatively, a shorter land length and more back pressure at the die plate can generate sinking characteristics due to less room for expansion. The type of starch used will affect the amount of gelatinization (or cook) of the fish feed. If a high quality starch is used then the sinking pellets will hold together better. Post-extrusion handling is also important to sort fines (especially with small diameter feeds < 2 mm) that may interfere with the ability of the feed to float vs sink.
3. Extrusion is an adaptable technology for generating shaped products, such as fish feed. Small changes in the formulation of the feed can affect pellet characteristics such as binding, size, shape, and sinking/floating. It is important to work with someone that has experience developing different types of fish feeds to match your application. It is possible to produce aquatic feed with small scale production (about 1 ton per hr), which results in a smaller investment in equipment. This also leaves potential to expand by adding more equipment as the business grows.
To summarize, final desired product will influence what type of extruder (single vs twin screw), scale of production, and types of ingredients you will use in your operation. Feel free to reach out if you have any further questions about the use of extrusion for developing fish feed.
Thank you, Joe Kearns, for starting and continuing the discussion on how extrusion can be used to produce high-quality fish feed.
If you are interested in learning more about the extrusion process and how it can be applied to the aquaculture industry, check out this short course in aquaculture hosted at Texas A&M by PERDC (https://perdc.tamu.edu/event/aquaculture-feed-extrusion-nutrition-and-feed-management-short-course/).