Screening antioxidant activity of seaweed extracts collected in the Vietnamese Mekong Delta for dietary supplementation of whiteleg shrimp Litopenaeus vannamei

Abstract

This study assessed the yield and antioxidant ability of seaweed extracts harvested from the Vietnamese Mekong Delta for the dietary supplementation of whiteleg shrimp, Litopenaeus vannamei. In the first experiment, a two-factor test was randomly designed, including three seaweed types (Chaetomorpha linum, Enteromorpha intestinalis, and Gracilaria tenuistipitata) combined with three solvent types (100°C hot water, 90% methanol, and 90% ethanol). The results indicate that C. linum extracted in hot water had a relatively high yield, total phenolic content, and the best antioxidant capacity, as illustrated by DPPH free radical scavenging, ferric chelating, and ferrous reducing power assays. In the second experiment, a feeding trial used the crude hot water extract of C. linum for juvenile L. vannamei. This experiment consisted of five treatments in which commercial feed was supplemented with crude extract at levels of 0 (control), 0.3, 0.6, 0.9, and 1.2%. Shrimp (mean weight: 0.65 ± 0.09 g) were raised in a total of 15 containers (volume: 500 L) with a density of 200 ind./m3. After 60 days of culture, shrimp survival showed no significant difference across treatments. Moreover, shrimp fed a 0.6% C. linum hot water extract diet had a significantly higher growth rate, production, feed efficiency, and digestive enzyme activity (trypsin, lipase, and amylase) than the control and other groups. Interestingly, polynomial regression revealed that a 0.52% extract diet gave the optimal feed conversion ratio, which was considered the appropriate supplementation level for L. vannamei.