Inclusion of duckweed (Lemna minor) in the diet improves flesh omega-3 long-chain polyunsaturated fatty acid profiles but not the growth of farmed Nile tilapia (Oreochromis niloticus)

Abstract

A 12-week experiment was conducted to determine the effect of dietary duckweed (Lemna minor) on growth performance, body composition and fatty acid profiles of juvenile Nile tilapia (Oreochromis niloticus). Five isonitrogenous (30 % crude protein) diets were prepared with the inclusion of dry ground L. minor at 0 %, 5 %, 10 %, 15 % and 20 % of diet dry weight. Each diet was randomly allocated to triplicate tanks stocked with juvenile tilapia that had an initial mean weight of 2.00 ± 0.01 g. The juvenile tilapia were reared in a flow-through system with each diet fed twice a day at a total ratio of 5 % body weight per day. While weight gain and specific growth rate (SGR) were generally higher, and food conversion ratio (FCR) generally lower in fish fed the control diet than fish fed L. minor, there were no significant differences in these performance parameters between tilapia fed L. minor at 15 % inclusion and fish fed the control diet. Survival ranged from 80 % to 96 % and was significantly higher in fish fed the control diet. Dietary L. minor significantly reduced whole-body total lipid contents and increased moisture contents. The dietary inclusion of L. minor significantly increased the proportions of omega-3 long-chain polyunsaturated fatty acids (LC-PUFA) in muscle, with eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids increasing by over 10-fold from 0.5 % each of total fatty acids, respectively, in fish fed the control diet to 5 % each in fish fed 20 % L. minor. Since the inclusion of L. minor increased the contents of 18:3n-3, but not EPA and DHA in the diets, this indicates that the increased proportions of EPA and DHA in the muscle of tilapia fed L. minor was due to endogenous biosynthesis of LC-PUFA with the conversion of dietary 18:3n-3 to EPA and DHA. Therefore, the present study indicated that dietary inclusion of 15–20 % L. minor in feeds for Nile tilapia can significantly improve the omega-3 fatty acid profile of muscle for human consumers, with only minor effects on growth and feed utilization. These findings demonstrated the potential for the utilization of L. minor as an ingredient to increase omega-3 LC-PUFA, EPA and DHA, contents of farmed tilapia while reducing the use of fish oil and fish meal in tilapia feeds.