Nutrient analysis and potential utilization value of Daphnia magna used as aqua-feed raw material

A trial was conducted to determine nutrient composition and heavy metal content of dried Daphnia magna from artificial-cultivation pond in spring, summer, autumn, winter and eutrophic lake sewage in summer, aiming to assess potential utilization value in aqua-feed. The results showed that there was significant seasonal difference in the moisture of artificial cultivated D.magna, and the highest was 5.14% in winter, and the lowest was 2.51% in summer. The moisture content (9.12%) of D.magna in summer sewage was significantly higher than that of artificial cultivation. The content of protein of artificially cultivated D.magna was 30.93% - 50.21% with significant differences in different seasons, and in winter and summer sewage was significantly higher than that of other groups. The total content of 15 amino acids determined markedly differed among groups, with the highest (36.65%) in winter and the lowest in summer (24.74%).In summer sewage, the amino acid content was 41.79%, and 9 essential amino acids accounted for 22.15%, lysine content reached 3.4 %, methionine 1.14 %, and threonine 2.45 %. The fat content was also significantly different with seasonal variation, the highest fat content was observed in winter (18.88%), while the lowest in autumn (4.19%), and no significant difference on the fat content was found in winter and summer sewage. The essential fatty acids were the highest in autumn and the summer sewage (17%), and the arachidonic acid and linolenic acid were not detected in all samples. The highest levels of heavy metal chromium, copper, zinc and lead appeared in summer sewage and artificial-cultivation pond in autumn, spring and summer, respectively, and no lead was detected in summer sewage and winter, no cadmium in all groups. Except for chromium, the lowest concentrations of copper, lead, arsenic and zinc were found in the summer sewage. All the results indicated that the D.magna was rich in protein and fat with lower potential toxicity of heavy metals, and both the essential amino acid and essential fatty acid nutrient values in summer sewage were generally higher than those of artificial cultivation, so it is more feasible to use D.magna in summer sewage as the feed protein source.