Effects of by-products from producing yacon (Smallanthus sonchifolius) juice as feed additive on growth performance, digestive enzyme activity, antioxidant status, related gene expression, and disease resistance against Streptococcus iniae in juvenile black rockfish (Sebastes schlegelii)

Abstract

This study investigated the effects of by-product from producing Smallanthus sonchifolius juice (BPSJ) as feed additives to juvenile black rockfish on growth performance, digestive and antioxidant enzymes activities, gene expression related growth and antioxidant status, and disease resistance against Streptococcus iniae. Five insonitrogenous and isolipidic experimental diets were formulated to contain five levels of BPSJ at 0 (control), 2.5, 5, 7.5 and 10 g kg−1 diet. At the end of 8 weeks feeding trial, compared with to BPJS0 group, we observed significant improvements in the growth performance (weight gain, specific growth rate, feed consumption, feed efficiency and protein efficiency ratio) among fish fed diets with increasing BPSJ level in the diet. Concurrently, plasma digestive enzymes (amylase, trypsin and lipase), lysozyme and antioxidant enzymes activities (superoxide dismutase, catalase and glutathione) were mostly higher in the groups fed with BPSJ supplemented diets. The gene expression related growth (insulin-like growth factor) and antioxidant status (superoxide dismutase, glutathione S-transferase and catalase) were upregulated by the addition of BPSJ in the diets. After challenged with S. iniae, the cumulative mortality was decreased by all levels of BPSJ supplementation. In conclusion, dietary supplementation of BPSJ can improve the growth performance, digestibility, antioxidant ability and disease resistance against Streptococcus iniae of juvenile black rockfish. © 2023 Elsevier B.V.