Green alga found on turbot skin lesions in chronic aeromoniasis case
Bottom line
A newly published case report in Veterinary Pathology describes what the authors say is the first documented instance of Ulva spp., a green marine alga, growing as an epibiont on the skin of turbot with chronic aeromoniasis. The report centers on a turbot farm in Galicia, Spain, where a February 2024 storm damaged infrastructure and left tanks uncovered, exposing already-injured fish to several days of intense solar irradiation. Afterward, staff noticed green tufts on affected fish. Necropsy of two turbots linked the lesions to chronic Aeromonas salmonicida infection, with exposed dermal tubercles colonized by Ulva and a biofilm that also contained A. salmonicida DNA. The authors concluded the algae were acting as surface colonizers rather than causing a new invasive infection. (eurekamag.com)
Why it matters: For veterinary professionals working in aquaculture, the case is a reminder that chronic skin lesions can become ecological niches after environmental disruption, creating unusual host-pathogen-environment interactions. In this report, the algae didn't appear to trigger additional host tissue responses beyond the underlying aeromoniasis, but the colonization may have mechanically delayed re-epithelialization, while the associated biofilm could function as a reservoir for the pathogen. That has practical implications for lesion monitoring, post-storm husbandry, tank protection, and biosecurity in marine fish systems, especially where A. salmonicida is already a concern in turbot production. (eurekamag.com)
What to watch: Whether additional farms or case series show similar algal colonization of chronic fish lesions, and whether management guidance evolves around post-weather-event surveillance and wound recovery. (eurekamag.com)
A case report in Veterinary Pathology details an unusual finding in farmed turbot: green tufts on the skin of fish with chronic aeromoniasis were identified as Ulva spp. growing as an epibiont on exposed dermal lesions. According to the report, the fish came from a farm in Galicia, northwestern Spain, after a February 2024 storm severely damaged the facility and left tanks uncovered. Farm staff then observed the algal growth on fish that already had chronic cutaneous disease linked to Aeromonas salmonicida. The authors say this is the first reported case of Ulva epibiosis on fish. (eurekamag.com)
The backdrop matters here. Chronic aeromoniasis in turbot can produce skin lesions severe enough to expose dermal tubercles, creating abnormal surfaces that may be colonized by other organisms. The storm appears to have changed the exposure conditions further by removing tank cover and allowing several days of intense sunlight, which likely altered the local environment around already-damaged skin. That combination, preexisting bacterial disease plus acute environmental disruption, seems to have created the conditions for an uncommon colonization event rather than a straightforward new infectious process. (eurekamag.com)
In the reported cases, two affected turbots were submitted for necropsy. Based on morphology, the surface growth was identified as Ulva spp. The algae were coated by a biofilm in which A. salmonicida DNA was detected by real-time PCR. Importantly, the authors reported that the algal presence did not induce additional host responses beyond the lesions already associated with chronic aeromoniasis, supporting the interpretation that this was true epibiosis, not tissue invasion by the alga. Even so, the colonization may have mattered clinically because the algae physically obstructed re-epithelialization and may have prolonged lesion chronicity. (eurekamag.com)
There isn't much published commentary yet on this specific case, but the broader disease context is well established. A. salmonicida remains an important pathogen in turbot and other aquaculture species, and recent transcriptomic work in turbot has continued to focus on host resistance and susceptibility, underscoring how significant this bacterium remains for fish health and production. That makes this report notable not because Ulva is suddenly a primary pathogen, but because it highlights how chronic bacterial disease can open the door to unexpected secondary colonizers in production settings. (pubmed.ncbi.nlm.nih.gov)
Why it matters: For veterinarians, diagnosticians, and aquaculture health teams, this is a useful reminder not to dismiss unusual surface growths as incidental contamination, especially after storms or other infrastructure failures. The practical lesson is that lesion ecology can shift quickly when fish with chronic skin disease are exposed to new light, water, or fouling conditions. If algae and biofilm are physically interfering with healing, then case management may need to focus not only on the primary bacterial disease, but also on environmental correction, wound progression, and whether colonized lesions are serving as pathogen reservoirs within the system. (eurekamag.com)
The report also has biosecurity implications. Because the Ulva was associated with a biofilm containing A. salmonicida DNA, the lesion surface may represent more than a cosmetic change. While the case report doesn't prove onward transmission from that biofilm, it raises a plausible concern that chronic lesions could help maintain pathogens in the farm environment. That's especially relevant for operations managing recurring aeromoniasis, where infrastructure damage, tank exposure, or delayed recovery after extreme weather could complicate control efforts. This is an inference drawn from the authors' findings rather than a demonstrated transmission pathway. (eurekamag.com)
What to watch: The next step is whether this remains a one-off pathology curiosity or becomes a recognized complication of chronic ulcerative disease in marine aquaculture. Follow-up reports could clarify how often epibiotic algae appear on chronic lesions, whether certain environmental triggers make colonization more likely, and whether farms should add targeted post-storm skin surveillance to standard health monitoring in turbot systems. (eurekamag.com)