Effects of feed processing method (extrusion and expansion-compression pelleting) on water quality and growth of rainbow trout in a commercial setting

Authors: Welker, Thomas; Overturf, Kenneth - Ken; SNYDER, SCOTT - Clear Springs Foods, Inc; Liu, Keshun; Abernathy, Jason; Frost, Jason; Barrows, Frederic

Submitted to: Journal of Applied Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/24/2018
Publication Date: 2/6/2018
Citation: Welker, T.L., Overturf, K.E., Snyder, S., Liu, K., Abernathy, J.W., Frost, J.B., Barrows, F. 2018. Effects of feed processing method (extrusion and expansion-compression pelleting) on water quality and growth of rainbow trout in a commercial setting. Journal of Applied Aquaculture. 30(2):97-124. https://doi.org/10.1080/10454438.2018.1433095.
DOI: https://doi.org/10.1080/10454438.2018.1433095

Interpretive Summary: The most commonly used feeds for salmonids in commercial aquaculture prior to the late 1980s were steam-compressed pellets. Steam-compressed pelleting, although still used to make fish feeds, has largely been replaced by dry extruded feeds in commercial aquaculture for most fish species. Compared to steam pelleted feed, extruded feeds are exposed to higher temperature and pressure during processing, which makes them more resistant to mechanical damage and stable in water and improves digestibility of carbohydrates in fish. High water stability of extruded feeds prevents rapid disintegration of pellets and the resulting solid waste that can contribute to poor water quality. We examined the effects of feed pellet processing (extrusion and expansion-steam pelleting) on feed quality, fecal stability, water quality, and growth performance in rainbow trout. We fed three types of feed pellets (expansion-steam pelleted [sinking], extruded sinking, and extruded floating) to juvenile rainbow trout at three feed rates (low, medium, and high) for 124 days. All feeds had similar chemical composition, but extruded feeds had a significantly higher degree of starch gelatinization than the expansion-steam pelleted feed, which led to extruded feeds having much higher water stability, fecal durability, and lower phosphorus discharge. Rainbow trout fed the extruded floating feed grew faster than those fed the two sinking feeds. Our work is the first to show that extruded feed pellets are not only more stable in water than pellets made by expansion-steam pelleting, but they also reduce fecal contributions to waste through improved fecal size and durability in water. The use of extruded feeds in commercial rainbow trout culture could improve waste collection and removal and reduce pollution in effluent.

Technical Abstract: To determine the effects of feed pellet processing (extrusion and expansion-steam pelleting) and on feed physico-chemical characteristics, fecal stability, water quality, and growth performance in rainbow trout, three types of trout feed pellets (compressed sinking, extruded sinking, and extruded floating) were prepared, analyzed, and fed to juvenile rainbow trout (initial weight = 285.8±15.2 g) at three feed rates for 124 days. Results showed that all feeds had similar chemical composition and water absorption curves with soaking time, but extruded feeds had a significantly higher degree of starch gelatinization than compressed feed, which led to extruded feeds having much higher water stability, fecal durability, and lower P discharge. Extruded floating feed produced better growth and feed conversion in rainbow trout than the two sinking feeds. Feed rate also contributed to better growth, but the improvements were not seen beyond feed rate 2. The present study is the first to show that the extrusion process not only produces pellets having better quality than the expansion-steam pelleting method but also improves fecal size and durability in water, and therefore, use of extruded feeds has the potential to improve waste collection and removal and reduce contribution to pollution in effluent.