Partial Replacement of Fishmeal with Duckweed (Spirodela polyrhiza) in Feed for Two Carnivorous Fish Species, Eurasian Perch (Perca fluviatilis) and Rainbow Trout (Oncorhynchus mykiss)

Two four-week feeding trials were conducted with fingerlings of Eurasian perch (Perca fluviatilis, 3.52 ± 0.08 g) and rainbow trout (Oncorhynchus mykiss, 1.49 0.05 fed graded levels dried (DWD) fermented (DWF) duckweed meal (Spirodela polyrhiza). The purpose these two was to evaluate DWD DWF as replacements for fishmeal. Fishmeal protein substituted by 12%, 24%, 35% compared control diets containing 40% (for perch) trout) fishmeal no duckweed. performance the fish (growth, feed conversion, lipid utilization) their whole-body composition evaluated control. While even lowest inclusion level, regardless its form (dried or fermented), resulted in significantly reduced perch, able utilize considerably well. Compared control, at a 12% showed an equal comparable percent weight gain (PWG; DWD: 377%, DWF: 373%), specific growth rate (SGR; 4.37%/day, 4.33%/day), conversion ratio (FCR; 1.11, 1.12), productive value (PPV; 21.5%, 21.2%). Increasing above both trout, most pronounced effects observed DWD35 group. All experimental diets, including affected whole body notably reducing content initial fish. initial, increased protein, lipid, ash contents. In conclusion, S. polyrhiza appears be promising ingredient when used maximum level while it should not considered ingredient.