“With only around one percent of our calcium silicates and silicon dioxides in the raw material formulations, we succeeded in manufacturing stable fish feed pellets with a total fat content of up to 37 percent. The total fat amount can be added as early as the extrusion stage,” comments Carolina Schillinger, Technical Market Manager 
Silica at Evonik. “And even at lower fat contents of between 11 and 37 percent, silica significantly increased the mechanical stability of the pellets under the applied extrusion conditions – by up to 60 percent depending on the fat level and silica type.” 

One reason for this is the tremendous absorption capacity of silica within its pores and interparticle spaces. As such, silica absorbs the oils like a sponge during extrusion. This enables an increased mechanical energy input and thus a good starch gelatinization even at higher fat contents. In turn, a high degree of starch gelatinization brings about a stable pellet structure and makes the starch easy to digest. “Moreover, we believe that fumed silicas (e.g. AEROSIL® 200 F) in particular interact with the starch polymers during gelatinization due to their network-forming properties. This immediately stabilizes the starch network,” explains Schillinger

Salmonoid feed manufacturers are not the only ones to benefit from this new silica application: In feed pellets for crustaceans, tropical freshwater fish and carnivorous marine fish such as sea bass, too, the ideal fat content can be adjusted quickly and easily by adding silica. In addition, the mechanical stability of the pellets is a relevant factor for all forms of aquaculture.

The development of balanced fish feed formulations for different species and pellet design are extremely complex due to the interplay of biochemical and mechanical factors, as the Leibniz Institute of Freshwater Ecology and Inland Fisheries describes on the website aquakulturinfo.de: “The basic mixture and extrusion determine the properties of the pellets when feeding. The most important factors are properties such as sinking behavior, durability in water, digestibility, size and taste.”

“With only around one percent of our calcium silicates and silicon dioxides in the raw material formulations, we succeeded in manufacturing stable fish feed pellets with a total fat content of up to 37 percent.” Carolina Schillinger, Technical Market Manager Silica at Evonik

The quality of the feed has a direct impact on the water quality. Firstly, pellets need to be stable enough not to disintegrate too early upon contact with the water. Secondly, they should taste good and be easily digestible in order to minimize the amount of feed residue and excrement left in the sea water (or in the closed water circuit in RAS facilities). Fish feed specialist Alltech®Coppens makes the following statement on this: “A RAS feed is characterised by high digestibility, leading to minimal amounts of faecal matter, and high protein retention characterised that minimises ammonia excretions so that the filters can work more efficiently. Next to that, high palatability is required for good feed intake and a composition that allows optimal growth. In trout, for example, this means a high-energy feed with a rather low ratio between digestible protein and digestible energy.”

Silica also allows the physical und the physiologically relevant properties of feed pellets to be optimized. This is relevant for the entire value chain from production to feeding: Solid, stable pellets are easier to store, transport and use. Moreover, adding silica reduces the amount of fat leakage when they are stored at higher temperatures. The pellets are more resistant to abrasion during transport and when passing through the feed system, in turn reducing dust, dirt and the amount of feed lost. The water stability and species-dependent sinking speed of the pellets also play a decisive role in a good feed intake and for water hygiene.