Tilapia processing byproduct treated with enzymatic hydrolysis and Rhodopseudomonas palustris is feasible for live feed culturing: Pathogen inhibition in vitro, live feeds microbiota, and Bidyanus bidyanus larviculture

Abstract

Fish processing byproducts are conventionally used in live feed production for larviculture because of their low cost and high productivity. However, waste-generated bacteria may cause pathogen proliferation, and antibiotics are widely used to reduce the bacterial loads of live feeds. In this study, tilapia processing byproducts were hydrolyzed into fish protein hydrolysate (FPH). Subsequently, the FPH was used to culture Rhodopseudomonas palustris, a photosynthetic bacterium (PSB), as a nutritional source for live feed. The results of the in vitro pathogen inhibition assay indicated that R. palustris significantly inhibited the growth of Aeromonas hydrophila, Edwardsiella tarda, Lactococcus garviae, and Streptococcus iniae in the FPH supernatant (p < 0.05). In practical live feed culture, untreated minced tilapia byproduct (control group) or FPH+PSB were used as nutritional sources for the live feeds. The V3-V4 region of the 16 S rRNA gene was amplified and sequenced for microbiota analysis. In the FPH+PSB group, Flavobacteriaceae and Alteromonadaceae were notably enriched. The Aeromonadaceae and Chitinophagaceae were reduced relative to the control group. Burkholdweiaceae, Rhodobacteraceae, Mor-axellaceae, and Pseudomonadaceae were the dominant bacterial families in both groups. To examine the effects of different live feed culturing methods on larviculture, the cultured live feed was fed to Bidyanus bidyanus larvae at 5 days posthatch (DPH). After 25 days of larviculture, the growth performance and survival rate of the FPH+PSB group were significantly higher than those of the control group (p < 0.05). These results indicated that treating tilapia byproducts with hydrolysis and R. palustris to culture live feed exerted a positive effect on B. bidyanus larviculture.