Title : First report of ocular pathology in Litopenaeus vannamei attributed to a novel Aeromonas species from the Kovalam Coast, India
Abstract:
Litopenaeus vannamei (whiteleg shrimp) is a cornerstone of global aquaculture, especially in India, due to its rapid growth and salinity tolerance. However, sustainability is increasingly challenged by multifactorial disease outbreaks linked to climate variability, antimicrobial misuse, and environmental degradation. While several pathogens of L. vannamei have been characterized, non-traumatic ocular infections remain undocumented.
During a routine epidemiological survey on March 17, 2025, in Kovalam, India, 6 out of 21 market specimens (28.6%) of L. vannamei exhibited conspicuous, milky-white ocular opacities. Histopathological examination of affected tissues revealed epithelial desquamation, focal necrosis, and leukocytic infiltration. Aerobic culturing yielded a consistent Gram-negative bacillus, which was identified by 16S rRNA gene sequencing (1,431 bp) as a putative novel Aeromonas species with 96.44% similarity to known taxa. The strain has been provisionally designated Aeromonas kovalamii sp. nov.
To trace its environmental origin and ecological relevance, gut content 18S rRNA-based DNA barcoding was performed. Identified prey included Paracalanus parvus, Microsetella norvegica, and Prionospio cirrifera organisms typical of eutrophic, polluted habitats. The gut metagenomics and microbiota were dominated by Proteobacteria, Bacteroidetes, Firmicutes, and other typical phyla, with opportunistic genera such as Vibrio, Shewanella, and Photobacterium detected. However, A. kovalamii was consistently isolated only from ocular lesions, not from gut or other tissues, suggesting its extrinsic role under stress-induced dysbiosis.
Phylogenetic analysis placed A. kovalamii in a distinct clade adjacent to A. dhakensis. Metabolite profiling via GC-MS identified bioactive compounds, including Pyrrolo[1,2-a] pyrazine-1,4-dione and Nitro-L-arginine. FTIR spectroscopy confirmed characteristic functional groups, while SDS-PAGE demonstrated distinct protein bands (70, 55, and 35 kDa), suggesting unique biosynthetic capabilities.
Diagnostic PCR assays ruled out major shrimp pathogens (WSSV, EHP, VpAHPND, IHHNV, and NHPB) in samples from hemolymph, hepatopancreas, gills, and muscle. This represents the first confirmed case of ocular pathology in L. vannamei caused by a novel Aeromonas species. These findings underscore the need for integrative diagnostics, environmental biomonitoring,
