Running Mortality Syndrome (RMS)

Running mortality syndrome describes a chronic production condition of farmed shrimp, especially Litopenaeus vannamei, characterized by low-level daily deaths (often 0.5 to 2 percent of biomass per day) that continue for weeks and do not respond to the usual emergency measures. Affected ponds show sluggish swimming, empty guts, pale or shrunken hepatopancreas, and poor feed response, while cumulative mortality can reach 30 to 60 percent of the crop over a cycle. RMS is considered multifactorial rather than a single-pathogen disease: contributing drivers include chronic Vibrio (especially V. parahaemolyticus) pressure, microsporidian infection such as Enterocytozoon hepatopenaei, mycotoxins in feed, high organic load, and sustained sublethal stress from poor water quality, low dissolved oxygen, or overcrowding. Diagnosis requires lab work (PCR for known agents, histology, bacterial isolation) because gross signs overlap with several other syndromes. Management focuses on stress reduction and load control: pond probiotics, sludge removal, moderate stocking densities, high-quality low-mycotoxin feeds, immunostimulants, and, where legal and prudent, targeted antimicrobial therapy under veterinary guidance. Prevention beats treatment; once a pond enters a running-mortality pattern, economics usually favor early partial harvest.