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Comparative Analysis of Gut Microbiota Between Fast-Growing and Slow-Growing Short-Finned Eels, Anguilla bicolor pacifica, and the Application of Bacillus tropicus FG2 as a Probiotic to Enhance Growth Performance of Eels
1
Department of Aquaculture, National Pingtung University of Science and Technology, Pingtung 912301, Taiwan
2
Department of Biological Science and Technology, National Pingtung University of Science and Technology, Pingtung 912301, Taiwan
*
Author to whom correspondence should be addressed.
†
These authors contributed equally to this work.
Animals 2026, 16(1), 54; https://doi.org/10.3390/ani16010054
Submission received: 28 October 2025
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Revised: 28 November 2025
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Accepted: 19 December 2025
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Published: 24 December 2025
(This article belongs to the Section Animal Nutrition)
Simple Summary
The gut microbiome strongly affects animal growth, physiology, and overall health. A balanced and diverse intestinal microbial community improves feed digestion, nutrient absorption, and gut barrier function, making microbiome stability a key factor in aquaculture performance. This study compares the intestinal microbiota of fast- and slow-growing eels to identify bacterial taxa linked to superior growth. Certain gut commensals may promote growth by enhancing digestion, producing enzymes, or regulating metabolic compounds. By isolating these beneficial strains, we aim to develop physiologically based probiotics for eel culture. The findings provide microbiome insights and functional strains that support evidence-based probiotic applications, offering practical value for improving eel health and farming efficiency.
Abstract
This study aims to investigate the differences in microbial community structure between fast-growing (FG) and slow-growing (SG) short-finned eels, Anguilla bicolor pacifica, using high-throughput 16S rDNA sequencing, and to evaluate the potential probiotic properties of Bacillus tropicus isolated from eel intestinal microbiota to enhance growth performance. High-throughput 16S rDNA sequencing revealed no significant differences in the α-diversity between FG and SG eels. Bacterial genera such as Cetobacterium, Clostridium, and Bacteroides were predominant in both groups, with Edwardsiella, Aeromonas, and Fusobacterium being more abundant in SG eels, suggesting a higher presence of potential pathogens. The analysis of the relative abundance of gut microorganisms revealed that SG eels harbored higher levels of potentially pathogenic bacteria, including Edwardsiella tarda and Aeromonas jandaei. In contrast, FG eels exhibited a greater abundance of the potential probiotic B. tropicus. Six strains of bacteria with relative abundance were isolated from the FG group, displaying superior digestive enzyme activity, including protease, lipase, amylase, cellulase, xylanase, and phytase, particularly strain FG2. Phylogenetic analysis confirmed that FG2 was closely related to B. tropicus. A virulence assessment confirmed the non-pathogenic nature of B. tropicus FG2, supporting its probiotic potential. Furthermore, feeding eels a diet supplemented with B. tropicus FG2 significantly enhanced growth performance, as evidenced by increased final weight percentages of weight gain and total production per tank (p < 0.05), while the proximate composition of the dorsal muscle showed an increase in lipid content (p < 0.05). These findings highlight B. tropicus FG2 as a promising probiotic for aquaculture applications.
