Enrichment effects of fermented by-product of Shochu distillery on Brachionus plicatilis sp. rotifer and larviculture performance in Japanese flounder (Paralichthys olivaceus)

Abstract

The effective use of distillery by-products of the shochu sweet potato has long been considered as a rich source of protein, fiber, amino acids, fatty acids, probiotics with a great potential as a functional feed for animals. This study applied fermented by-product of Shochu distillery (FBPSD) and salmon roe emulsion oil for rotifer enrichment to evaluate its effects on the: (i) nutritional composition of rotifers and (ii) feeding responses of Paralichthys olivaceus larvae when fed with enriched rotifers. The salmon roe oil enrichment was set as a control diet and FBPSD was supplemented at different doses (1, 5 and 10 % based on the salmon roe oil amount). The results showed that the rotifers supplemented with FBPSD at 5 and 10 % significantly enhanced protein, carbohydrate, and HUFA content. Similarly, the activity and expression profiles of targeted enzymes including trypsin, chymotrypsin, lipase and amylase effectively responded at early and middle-metamorphosis of the larvae to 5 and 10 % enrichment regiment. These two treatments were also found to be better supported in energy metabolism evidenced by Cytochrome-C-Oxidase (cox) and ATPase-pk (atp) gene expression in the larvae. Moreover, the expression levels of immune-related genes (IL-10, IL-1β, TNF-α, P2Y6) and antioxidant-related genes (SOD, CAT) were significantly improved at 5 and 10 % of FBPSD. Cessation of feeding and delay in growth during the metamorphic process was also molecularly demonstrated. Larvae suffered low survival (24.5–25.3 %) in control and 1 % supplementation of FBPSD, but significantly improved at 5 and 10 % (36.4–38.7%). However, the growth performance of larval fish was not remarkable after 40 days of culture. The results of this study revealed that FBPSD could be considered as a potential supplementary enrichment for live feed in fish larviculture, especially at 5 and 10 % rotifer enrichment dosage.