Submitted to: World Aquaculture Magazine
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/1/2003
Publication Date: 11/1/2003
Citation: Schwertner, M.A., K.K.M. Liu, F.T. Barrows, R.W. Hardy, F.M. Dong. 2003.Performance of Post-juvenile Rainbow Trout Onchorynchus mykiss Fed Diets Manufactured by Different Processing Techniques. World Aquaculture. 34(2):162-174 Interpretive Summary: We evaluated the effect of different processing methods on the physical characteristics of the feed and the growth of rainbow trout fed these feeds. Pellets were produced by cooking extrusion (CE), steam pelleting/compaction pellet (SP), Universal Pellet Cooker (UPC), and expansion (E). Feeds were fed to rainbow trout for 16 weeks at the Hagerman Fish Culture Experiment Station. The method of feed manufacture did affect both the physical characteristics and fish performance. Fish fed the E feed had the lowest weight gain and the highest feed conversion ratio. The degree of starch gelatinization (cooking), sinking rate and percent floating was also affected by processing method. Fish farmers should select the type of pellet processing method based upon specific conditions in their hatcheries.
Technical Abstract: Four different methods of pelleting-extruded (EXT), steam pelleted (STM), using a Universal Pellet Cooker (UPC), and expanded (EXP)—were performed on subsamples of a single batch of mash to determine the effects on feed pellet characteristics, in vivo feed digestibility, and performance of rainbow trout Oncorhynchus mykiss fed the diets for 16 wk. Results indicated that the STM feed was the most (851 g/L) and UPC feed the least (672 g/L) dense, and that UPC feed had the highest % float (8.3%) and, of the pellets that sank, the fastest sink rate (15.1 cm/sec). While some differences occurred among pelleted diets in loss of dry matter (% dry loss) after incubation in a water bath for up to 10 min, the overall % dry loss was only approximately 1-2%. The method of pelleting did not affect fish weight gain, feed conversion ration, or specific growth rate. Measurement of the apparent digestibility coefficient of dry matter of the test diets using Cr2O3 as the marker ranged from 71-89%. While it appeared that the method of pelleting can affect feed characteristics and the amount of feed offered to the fish, fish performance was not affected.