The aquaculture industry is growing rapidly worldwide, and land-based aquaculture is also thriving in Japan. Salmon is currently the most consumed fish in Japan, with particularly high demand for trout salmon, which is suitable for raw consumption in sushi and other dishes. Although most trout salmon is currently imported, domestic trout salmon production is thriving in various regions across Japan. However, the aquaculture industry faces various challenges, including the depletion of fish meal, a key feed ingredient, and the occurrence of fish diseases. For example, salmonid fish such as rainbow trout are known to develop enteritis when fed diets containing soybean meal, a fish meal alternative, leading to restrictions on its use and necessitating countermeasures. Additionally, in terms of disease control, the global spread of antibiotic-resistant genes has made it essential to develop strategies that minimize reliance on antibiotics. One promising approach is to promote "gut health" in fish. In humans, the importance of short-chain fatty acids has been increasingly recognized in recent years. Among these, butyrate serves as an energy source for colon epithelial cells and is known to have anti-inflammatory effects, making it essential for maintaining a healthy intestinal environment. As a result, interest in butyrate-producing bacteria, alongside lactobacilli, has been growing.

The research using Clostridium butyricum, a type of butyrate-producing bacterium used as a probiotic in humans, has begun in the aquaculture field. While certain effects such as growth promotion have been recognized, most Clostridium butyricum strains are of mammalian origin, with an optimal growth temperature of around 37 °C. On the other hand, the optimal growth temperature for fish such as rainbow trout is 18 °C or lower, making it difficult for these microorganisms to establish themselves in the intestines of fish, particularly cold-water fish. As a result, there has been a growing demand for butyrate-producing bacteria derived from fish, which are more suitable with intestinal environment and temperature of aquaculture species.

Researchers at AIST and Shiga Prefectural Fisheries Experiment Station have discovered butyric acid-producing bacteria from fish intestines for the first time in the world.

In recent years, the aquaculture industry has experienced rapid global growth, with land-based aquaculture also becoming active domestically. However, the industry faces various challenges, including the depletion of fish meal, a key feed ingredient, and the occurrence of fish diseases. As a result, research has been conducted on technologies to address these issues through "gut health" in fish, such as disease suppression and growth promotion. Recent findings have shown the beneficial effects of butyrate-producing bacteria on human intestinal health, leading to research on the use of mammalian-derived butyrate-producing bacteria in aquaculture. However, the optimal temperature for mammalian-derived butyrate-producing bacteria differs significantly from the growth temperature of fish, posing challenges in terms of colonization. The discovery of butyrate-producing bacteria in rainbow trout intestines opens the door to new intestinal health technologies for fish using "fish-specific butyrate-producing bacteria." In the future, these bacteria could be utilized as probiotics to improve aquaculture technologies for rainbow trout and other fish, such as trout salmon produced through offshore aquaculture, contributing to reducing economic losses from fish diseases and promoting the use of alternative feed ingredients.

Journal: International Journal of Systematic and Evolutionary Microbiology
Title of paper: Piscibacter tructae gen. nov., sp. nov., an anaerobic butyrate-producing Fusobacteriaceae bacterium isolated from the gut of rainbow trout
Authors：Mio Takeuchi and Kazuhiro Sugahara
DOI: 10.1099/ijsem.0.006877