Messi Biology states that the hallmark of blister disease in Macrobrachium rosenbergii (giant freshwater prawn) is the formation of transparent blisters measuring 3 to 8 millimeters under the carapace, containing a light-yellow turbid fluid. This condition is frequently accompanied by symptoms such as prawns gathering at the pond edges, reduced feed intake, pale hepatopancreas, and soft shells. The pathogen responsible is Citrobacter freundii. Its optimal breeding conditions are precisely a water temperature of 30–32°C and a low-salinity, weakly acidic environment with a pH of 6.0–7.0. Ponds with dirty bottom sludge, excessive uneaten feed, and low dissolved oxygen are particularly prone to outbreaks. Magnesium hydroxide is not a “miracle drug” for eradicating the pathogen; rather, it is a chemical auxiliary whose core value lies in gently adjusting pH, purifying bottom sediments, and supplementing magnesium, thereby disrupting the survival breeding ground of the pathogens from the environmental source.
Magnesium hydroxide can precisely regulate pH, cutting off the optimal breeding zone for pathogens. As a weak base, magnesium hydroxide is slightly soluble in water. This “limitation” is precisely its key advantage as an environmental remediation auxiliary. Upon entering the water, it continuously and slowly dissociates magnesium ions and hydroxide ions, steadily raising the water pH to the 8.5–9.0 range—the exact window where acidophilic bacteria such as Citrobacter freundii struggle to reproduce, and sulfate-reducing bacteria (SRB) cannot survive. Once SRB are inhibited, the production chain of hydrogen sulfide in the bottom sludge is severed, reducing the risk of “bottom poisoning” at the source. More importantly, magnesium hydroxide features a natural pH buffering ceiling; even if applied in excess, the pH will not surge to levels that burn the gills or irritate gill filaments, unlike quicklime or caustic soda. In professional terms, it is a “non-hazardous, non-corrosive pH regulator with natural buffering capacity,” rather than a bactericidal drug.
Magnesium hydroxide can adsorb harmful substances in bottom sludge, purifying the “hiding soil” for bacteria. Bottom sludge is the true “stronghold” of the pathogens causing blister disease. After magnesium hydroxide particles are introduced into the pond, they act on one hand through electrostatic adsorption to capture suspended organic particles in the sludge and water column, promoting flocculation and sedimentation. On the other hand, they can adsorb free hydrogen sulfide and further oxidize it into odorless, non-corrosive magnesium sulfate, achieving a transformation of “replacing toxicity with salt.” It also possesses complexation and precipitation capabilities for ammonia nitrogen, excess phosphates, and heavy metal ions such as copper, lead, cadmium, and mercury. Studies show that its total phosphorus removal rate in shrimp aquaculture wastewater can reach over 96%. Treated sediment gradually shifts from “dirty, acidic, and toxic” to “clean, alkaline, and stable,” depriving pathogens of the organic matter and anaerobic environment they depend on for growth. This is a comprehensive bottom-remediation process based on physicochemical actions, rather than any form of bactericidal treatment.
Magnesium hydroxide can supplement magnesium ions, enhancing the shrimp’s own resistance. Magnesium is a key element for shrimp shell hardening, osmotic pressure regulation, and enzymatic metabolism. A deficiency in magnesium directly leads to molting difficulties and an increased proportion of soft-shelled shrimp, providing an opportunity for opportunistic pathogens. The magnesium ions slowly released by magnesium hydroxide can be indirectly utilized by the shrimp to work synergistically with sodium and potassium ions in maintaining intracellular and extracellular osmotic pressure balance, alleviating high-temperature heat stress, increasing feed intake during high-temperature periods, and lowering the disease incidence from a physiological level. During high-temperature seasons, calcium and magnesium ions in the water are prone to precipitation and loss due to vigorous algal photosynthesis. At this time, using magnesium hydroxide as an external magnesium source supplementation provides effective support for feed formulations and mineral nutritional regulation.