New bacterial culprits uncovered in Brazilian aquaculture
Researchers in Brazil have identified a suite of harmful bacteria that can trigger a severe disease known as columnaris in fish raised for human consumption. The investigation, recently published in the journal Microbial Pathogenesis, marks the first time several bacterial species have been linked to this condition within the country. Samples were taken from Nile tilapia, the most widely cultivated species, as well as from native fish such as piranhas, carp‑salmon and members of the antenna‑catfish group.
Understanding columnaris and its impact
Columnaris manifests as white lesions on the skin and fins, and can cause rapid deterioration of the gills, often leading to death within days. Although sometimes called “mouth fungus,” the disease is bacterial, not fungal. The pathogens feed on cells that line the exterior of the fish, a process that is especially lethal for larvae and juveniles.
Diverse bacterial lineup
The team isolated eleven bacterial strains from diseased specimens. Six of them belonged to Flavobacterium oreochromis, a bacterium previously reported only in Nile tilapia. The same organism was now detected in piranhas and carp‑salmon, expanding its known host range. In addition, the scientists recorded the presence of Flavobacterium davisii in antenna‑catfish for the first time, indicating that the pathogen can cross taxonomic boundaries. Molecular analyses also revealed F. indicum and F. inkyongense, species that until now had been documented mainly in Asia and the United States.
Why detection is tricky
Some of the colonies are almost invisible on standard growth media because the bacteria glide across the surface, leaving only faint traces. The researchers warn that laboratory technicians must scrutinize plates carefully, adjusting the type of agar to improve visibility.
Temperature, biofilm formation and farm‑level consequences
Experiments conducted at 20 °C, 28 °C and 35 °C showed that many isolates produce abundant biofilm at 28 °C. Biofilm creates a protective matrix that shelters the microbes until conditions become favorable again. In fish farms, these slimy layers can coat trays, nets and other equipment, allowing the bacteria to persist despite routine cleaning. The study therefore underscores the necessity of rigorous disinfection protocols to prevent long‑term colonisation of production infrastructure.
Heat‑loving strains raise concerns
One isolate, F. indicum, grew most vigorously at 35 °C, suggesting that rising water temperatures could give it a competitive edge. Conversely, F. davisii showed reduced motility at the same high temperature, highlighting the varied thermal preferences among the pathogens.
Overall, the findings broaden the known spectrum of fish species vulnerable to columnaris and reveal how adaptable these bacteria are to Brazil’s warm aquatic environments. For aquaculture operators, the message is clear: vigilant monitoring, temperature management and thorough sanitation are essential tools to curb the spread of these emerging threats.
Source: https://scientias.nl/ziekmakende-bacterien-verspreiden-zich-onder-braziliaanse-kweekvissen/