Abstract
The greater duckweed Spirodela polyrhiza (Lemnaceae) is a free-floating freshwater macrophyte. The effect of dietary inclusion of duckweed in the feed of common carp Cyprinus carpio fry was evaluated. The control feed (SP0) contained soybean meal as the primary protein source. In four experimental feeds, greater duckweed was incorporated at levels of 5% (SP5), 10% (SP10), 15% (SP15), and 20% (SP20) replacing soybean meal. Broken-line regression showed that incorporation of greater duckweed at 10 and 13.4% levels were the breakpoint for final weight and specific growth rate (SGR) of fish, respectively. The final weight and SGR of common carp fed diet SP20 were significantly higher compared with those of others. The feed conversion ratio was lowest in SP20 treatment. The inclusion of greater duckweed in the fish feeds showed linear relationships with amylase, trypsin, chymotrypsin, and lipase activities. The content of crude protein was significantly higher in SP10, SP15, and SP20 treatments compared with that of others. Significantly higher crude lipid and ash contents were found in SP20 diet-fed fish compared with other diet-fed fish. The essential amino acids composition was similar in five different diet-fed fish. The greater duckweed supplemented feeds influenced the fatty acid contents of fish. The monounsaturated fatty acids (MUFA) showed an inverse relationship with the inclusion level of greater duckweed in the feed. The highest MUFA content was found in fish fed SP0 diet. The highest level of linoleic acid was found in SP20 diet fed fish. The n-3 PUFA contents of fish showed an increasing trend with the increasing inclusion of greater duckweed, and a significantly higher level was found in SP20 compared with that of others. A significantly higher expression of fas was found in SP5 and fads2d6 in SP5 and SP10 compared with that of others. The expressions of elovl2 and elovl5 were significantly higher in SP5, SP10, and SP15 diet-fed fish compared with other diet-fed fish. The incorporation of greater duckweed in diets improved the growth performance and nutritional value of common carp.
Highlights
The application of freshwater macrophytes as fish feed ingredients is an emerging area of research
The control feed (SP0) contained soybean meal as the only primary source of protein, while in the four experimental feeds, greater duckweed was incorporated at the levels of 5%, 10%, 15%, and 20% of total feed at the expense of soybean meal, wheat flour, corn meal, and sunflower oil to produce feeds SP5, SP10, SP15, and SP20
The soybean meal was replaced in a graded manner, which resulted in changes in the proportions of amino acids in the feeds
Summary
The application of freshwater macrophytes as fish feed ingredients is an emerging area of research. The nutritional value (e.g., amino acid and fatty acid compositions, fiber content, and flavorings) of ingredients should be considered during fish feed formulation (Gatlin et al, 2007; Glencross et al, 2020). Meals and other products of soybean are the most commonly used plantbased ingredients in the aqua feed industry. There is a need to find other, non-conventional ingredients that have less or no use in other feed sectors, but that still have high-quality nutritional profiles with all the required amino acids and fatty acids. The greater duckweed Spirodela polyrhiza (family: Lemnaceae) is a free-floating freshwater macrophyte that has been considered as a suitable feed ingredient for both fish and livestock (FAO, 2001; Hasan and Chakrabarti, 2009; Cruz-Velásquez et al, 2014; Chakrabarti, 2017)
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