Enrichment of Daphnia magna with Canola Oil and its Effects on the Growth, Survival and Stress Resistance of the Caspian Kutum (Rutilus frisii kutum) Larvae

In freshwater larviculture, Daphnia species have received considerable attention as live food. This study examined the use of canola oil to enrich Daphnia magna as a function of enrichment duration. The experiment compared four enrichment durations (3, 6, 9, and 12 h) with a non-enriched control group. An enrichment time up to 6 h resulted in the highest amounts of polyunsaturated fatty acids (PUFAs) in the fatty acid profile of D. magna. Afterward, D. magna enriched within 6 h was fed to Rutilus frisii kutum larvae (initial weight of 52.62 mg) for 14 days in order to compare performance of these larvae with those fed non-enriched D. magna and also with larvae fed a commercial dry feed (Biomar). Specific growth rates (SGR) showed significant differences (P <= 0.05) between larvae fed enriched D. magna and Biomar-fed fish. Larvae fed enriched and non-enriched D. magna presented total weight and length (173.1 mg and 31.3 mm) and (150.1 mg and 27.5 mm, respectively), and the lowest values (138.4 mg and 25.8 mm) were recorded in larvae fed Biomar. Survival rates during the larval culture period and resistance of larvae against salinity (25 parts per thousand) stress were not statistically different (P >= 0.05) among the treatments. However, a salinity stress of 13 parts per thousand led to significant differences (P <= 0.05) with highest survival (93.33%) in fish fed 6-h-enriched D. magna. Enrichment of D. magna with canola oil can be applied as a useful method to increase the stock enhancement of such valuable species as R. frisii kutum.