Red Tide Algal Toxin-Induced Intestinal Injury in Marine Fish: Mechanisms, Gut Microecology, and Aquaculture Health Risk Assessment

Harmful algal blooms (HABs) can cause rapid, extensive mortality in exposed marine fish, often before fish-level diagnostic sampling can guide an emergency response. This review compares the toxin-specific evidence for intestinal injury caused by paralytic shellfish toxins, okadaic acid and Dinophysistoxins, brevetoxins, and fish-killing blooms, while distinguishing direct evidence in marine fish from evidence in other models. Intestinal barrier disruption, inflammation, and microbiome changes are valuable for explaining sublethal exposure, survivor recovery, and post-event attribution. They are not proposed as operational triggers during an acute fish kill. Practical management instead depends chiefly on site-specific environmental surveillance before exposure, predefined emergency actions when a bloom approaches, and longer-term reduction in avoidable nutrient and waste inputs where these contribute to local bloom risk. A four-stage framework links environmental hazard, fish exposure, biological effects, and production or food-safety outcomes with quantitative indicators and explicit uncertainty at each transition. This revised scope places mechanistic intestinal toxicology within the ecological time scale and operational limits of marine aquaculture.