Hideaki Takahashi

Abstract Dietary 1-kestose in rainbow trout was associated with higher Clostridiaceae abundance and descriptively higher survival during natural infectious hematopoietic necrosis exposure. To explore a possible microbial basis, we examined GH32 enzymes from fish-derived probiotic Clostridium butyricum LZK-08. Phylogeny-guided testing of E. coli-expressed GH32s identified plasmid-encoded LZK-GH32-2 (XTP15357.1) as a 1-kestose-degrading enzyme, suggesting strain-specific GH32 repertoires may underlie selective prebiotic responses.

Aims: To evaluate whether dietary co-supplementation with 1-kestose (Kes) and heat-killed Lactiplantibacillus plantarum FM8 (FM8), collectively termed Kes+FM8, affects survival, growth performance, and intestinal microbiota composition in juvenile abalone (Haliotis discus discus). Study Design: A preliminary, large-scale, controlled hatchery feeding trial with two dietary groups, one tank per treatment, and approximately 10 months of post-supplementation follow-up. Place and Duration of Study: Shizuoka Prefectural Thermal Effluent Utilization Research Center, Omaezaki, Shizuoka, Japan. The 60-day intervention was conducted from June 24 to August 23, 2024, followed by approximately 10 months on a standard diet. Methodology: Juvenile abalone (initial shell length approximately 15 mm; approximately 22,500 per group) received either a control diet or a Kes+FM8-supplemented diet containing 1% Kes and 0.1% heat-killed FM8 for 60 days. Survivor numbers were estimated daily, shell length was assessed on Days 0, 20, 40, 60, and 360, and intestinal microbiota was analysed in visceral tissue samples from nine abalone per group at Day 60 by 16S rRNA gene sequencing. Results: Although both groups experienced a marked mortality event coinciding with elevated seawater temperatures, the number of surviving abalone in the Kes+FM8 group remained higher and was approximately 1.5 times that in the control group at Day 360. Shell length did not differ during supplementation but was greater in the Kes+FM8 group at Day 360 (P < 0.001). At Day 60, the Shannon index was higher (P = 0.024), and microbial community composition differed between groups (PERMANOVA, P ≤ 0.001). The relative abundance of the Shewanella algae group was higher in the Kes+FM8 group. Conclusion: These preliminary findings suggest associations between Kes+FM8 supplementation and survival, growth, and microbiota composition; however, dietary and tank effects could not be distinguished. Replicated tank-level trials including Kes-only and FM8-only groups are needed to evaluate efficacy.