Indian Shrimp Pathology Compendium

White Gut Syndrome (WGS) and White Feces Syndrome (WFS) represent one of the most commercially devastating gastrointestinal pathologies in Indian Litopenaeus vannamei culture. Characterized by the progressive detachment and aggregation of transformed microvilli (ATM) from the hepatopancreatic tubule epithelial cells, the disease leads to chalky white fecal strings floating on feeding trays, feed collapse, and secondary vibriosis.

Enterocytozoon hepatopenaei (EHP) is an intracellular microsporidian parasite that replicates exclusively within the tubule epithelial cells of the penaeid shrimp hepatopancreas. Unlike acute viral pathogens that cause rapid catastrophic mortality, EHP causes severe nutrient absorption failure, leading to profound growth stunting, size disparity (coefficient of variation > 35%), elevated FCR (> 1.8), and extreme vulnerability to secondary White Feces Syndrome and bacterial vibriosis.

Acute Hepatopancreatic Necrosis Disease (AHPND), historically termed Early Mortality Syndrome (EMS), is an acute virulent bacteriosis caused by specific strains of Vibrio parahaemolyticus (and related species) acquiring the 70-kb pVA1 conjugative plasmid encoding the PirA^vp and PirB^vp binary pore-forming toxins. It typically strikes within the first 10 to 35 days of culture (DOC), causing massive acute mortality up to 100% within 48 to 72 hours if left unmanaged.

Ammonia ($NH_3$) and Nitrite ($NO_2^-$) toxicity represent the primary environmental asphyxiation emergency in semi-intensive and intensive shrimp aquaculture. While ionized ammonium ($NH_4^+$) is relatively non-toxic, un-ionized ammonia ($NH_3$) diffuses freely across gill membranes, inducing branchial hyperplasia, osmoregulatory collapse, and blood pH alteration. Simultaneously, nitrite oxidizes hemocyanin copper ($Cu^{2+}$), rendering hemolymph incapable of oxygen binding, leading to suffocation even under saturated dissolved oxygen conditions.

Luminescent Vibriosis is an acute to sub-acute bacterial infection caused primarily by bioluminescent Vibrio harveyi (and related Vibrio campbellii). Characterized by quorum sensing-mediated expression of luciferase enzymes ($luxCDABE$ operon), infected moribund shrimp and nursery larvae glow with a greenish-blue luminescence in total darkness. The bacteria produce potent extracellular proteases, hemolysins, and chitinases that dissolve cuticular membranes and hepatopancreatic tubules, leading to widespread systemic septicemia and Red Disease.

Running Mortality Syndrome (RMS) is a distinct clinical manifestation predominantly documented in intensive Litopenaeus vannamei farming across coastal Andhra Pradesh (West Godavari, Krishna, Bapatla, and Nellore districts). Unlike acute WSSV or AHPND which cause total pond wipeout in 72 hours, RMS is characterized by continuous, low-grade, persistent daily mortalities (10 to 50 dead shrimp per check tray or 5–15 kg/day) persisting over 15 to 30 days between DOC 35 and DOC 70, gradually eroding 30% to 60% of crop biomass.

Black Gill Disease is an inflammatory branchial pathology characterized by brown, dark brown, or jet-black discoloration of the shrimp gill lamellae. Unlike a single pathogen disease, black gill represents an advanced hemocytic melanization response (prophenoloxidase-activating system) triggered by three primary etiologies: fungal hyphal invasion (Fusarium solani), severe benthic organic sludge and silt accumulation, or chronic exposure to toxic heavy metals and un-ionized hydrogen sulfide ($H_2S$). As melanized hemocyte nodules occlude the branchial micro-vessels, shrimp suffer severe hypoxia, respiratory suffocation, and secondary mortality during molting.

Loose Shell Syndrome (LSS) and Soft Shell Syndrome (SSS) are chronic osmoregulatory pathologies characterized by failure of the shrimp exoskeleton to sclerotize and calcify post-ecdysis. In LSS, an abnormal fluid-filled space develops between the soft, flaccid cuticular exoskeleton and the underlying abdominal musculature. In SSS, the cuticle remains paper-thin, soft, and wrinkled for days post-molt. The condition is triggered by ionic mineral imbalances (especially $Ca:Mg:K$ ratios in low-salinity borewell waters), severe calcium/phosphorus metabolic failure, and chronic sub-clinical nutritional exhaustion.

Benthic black soil accumulation and Hydrogen Sulfide ($H_2S$) toxicity constitute the primary stealth killer of benthic-feeding penaeid shrimp. Uneaten feed, fecal casts, and dead plankton settle on the pond bottom, creating a dense anaerobic organic sludge blanket. Obligate anaerobic sulfate-reducing bacteria (Desulfovibrio spp.) reduce sulfate ($SO_4^{2-}$) to highly toxic un-ionized hydrogen sulfide ($H_2S$). Even trace concentrations ($> 0.01 ext{ mg/L}$) damage shrimp mitochondrial cytochrome c oxidase, paralyze branchial respiration, and cause instantaneous mortality when shrimp burrow into bottom sediments.

White Spot Syndrome Virus (WSSV) is a large, rod-shaped, enveloped, double-stranded DNA virus belonging to the Nimaviridae family. It represents the single most destructive viral pathogen in penaeid shrimp culture worldwide. Characterized by pathognomonic 0.5 to 2.0 mm calcified white spots on the inner surface of the cephalothorax carapace and cuticular abdominal somites, WSSV causes acute systemic destruction of ectodermal and mesodermal tissues, resulting in 100% mortality within 3 to 5 days of onset.

Infectious Myonecrosis Virus (IMNV) is a non-enveloped, double-stranded RNA virus belonging to the Totiviridae family. It causes extensive focal to confluent coagulative muscle necrosis primarily within the striated abdominal musculature and tail fan of Litopenaeus vannamei. Affected muscle tissue becomes opaque, chalky-white, and milky, frequently followed by secondary reddish discoloration in advanced stages. Acute mortalities are heavily provoked by sudden environmental shocks, including rapid temperature swings, salinity drops, and low dissolved oxygen.

Zoothamnium, Epistylis, and Vorticella are sessile, colonial peritrichous ciliated protozoans that attach ectocommensally to the exoskeleton, eyes, appendages, and branchial lamellae of cultured penaeid shrimp. While these protozoans do not invade internal host tissues directly, dense colonies form a thick, fuzzy, moss-like carpet over the gills and cuticle. This fouling traps suspended organic detritus, severely impairs branchial gas exchange, impedes swimming motility, and prevents successful ecdysis molting, leading to widespread suffocation during low-DO periods.