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

Abstract

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

Partial Replacement of Fish Meal with an Aquatic Macrophyte, Ceratophyllum demersum in the Diet of Common Carp, Cyprinus carpio var. communis Fingerlings

“…The results of the present study are congruent with those of other researchers who have suggested that fish meal can partially be replaced with aquatic macrophytes [8,[44][45][46][47][48][49]. The results of the growth characteristics and feed consumption of C. carpio var.…”

“…In order to reduce the cost of fish feed in aquaculture and to ensure a sufficient supply of nutrients for optimum growth, less expensive protein source from both plant and animal origin have been studied as prospective substitutes for fish meal [7]. The sustainability of aquaculture could be increased by substituting a more sustainable protein source that does not compete with human food for fish meal in the diets of fish fries and fingerlings [8]. Scientists must therefore devise new methods to supply the necessary quantities of high-quality protein in order to satisfy the expanding demand [9].…”

Duckweed production on diluted chicken manure

“…They are among the most rapidly growing vascular plants, making them highly efficient and fast protein producers worldwide, surpassing soybeans several-fold in terms of unit time and area (Xu et al, 2012;Leger et al, 2021;Stadtlander et al, 2022). Duckweeds have been utilised as animal feed for a variety of monogastric animals, including fish (Stadtlander et al, 2023), pigs (Rojas et al, 2014) and poultry (Haustein et al, 1990), and are therefore considered a potential future protein source in animal feed (Sońta et al, 2019).…”