Novel Bacterial Shell Disease Syndrome in the Mud Crab Scylla serrata (Forskål, 1775) from the Pichavaram Mangrove Ecosystem, Southeast Coast of India
Silambarasan Durai
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
Keerthika Ganesan
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
Vasanthan Koothan
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
Ayyaru Gopalakrishnan
Department of Biotechnology, School of Basic Sciences, Takshashila University, Ongur-604305, Tindivanam Taluk, Villupuram District, Tamil Nadu, India.
Deepa John
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
Anirban Kundu
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
Sibiraj Yuvaraj
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
Vijayanand Packiaraj *
Centre of Advanced Study in Marine Biology, Faculty of Marine Sciences, Annamalai University, Parangipettai 608 502, Tamil Nadu, India.
*Author to whom correspondence should be addressed.
Abstract
Shell disease syndrome is characterised by progressive alterations of the crustacean cuticle and may involve interactions among the host, microorganisms, and environmental conditions. This study aimed to (i) characterize the morphological and histopathological changes associated with shell lesions in the wild mud crab Scylla serrata and (ii) characterize lesion-associated Aeromonas through 16S rRNA gene sequence analysis. A crab exhibiting conspicuous rust-brown to dark-brown lesions on the appendages and ventral body surface was collected from Mudasalodai Fishing Harbour adjacent to the Pichavaram mangrove ecosystem, southeast coast of India. Gross pathological observations were recorded, and tissue samples were fixed, processed by routine histological procedures, sectioned, and examined microscopically to assess tissue and cellular alterations. For molecular characterisation, DNA from lesion-associated material was subjected to PCR amplification and sequencing of the 16S rRNA gene, followed by sequence comparison and phylogenetic analysis with reference Aeromonas sequences. Histological examination revealed disruption of the gill cuticle and underlying epithelium, infiltration of eosinophilic granular haemocytes, and formation of haemocyte plugs or nodules. The hepatopancreas showed an increased abundance of B-cells around the basal lamina and the tubular lumen. Two 16S rRNA gene sequences obtained from lesion-associated material, designated AH01 and AH02, occupied different positions within the Aeromonas sequence dataset, with bootstrap support values of 64% and 79%, respectively, and were provisionally identified as Aeromonas hydrophila. The findings demonstrate an association between external shell lesions, internal tissue responses, and lesion-associated Aeromonas DNA in the examined crab. However, because the study was restricted to a single specimen and bacterial causality was not experimentally established, further sampling, bacterial isolation, and molecular confirmation are required to determine the potential role of Aeromonas in shell disease of wild S. serrata.
Keywords: Scylla serrata, mud crab, Pichavaram mangroves, shell disease syndrome, cuticular lesions, histopathology, gill epithelium, hepatopancreas, haemocyte nodules, Aeromonas hydrophila, 16S rRNA gene sequencing