RESEARCH ARTICLE Morphological specializations of the epidermis of an angler catfish Chaca chaca (Siluriformes, Chacidae) in relation to its ecological niche: A scanning electron microscopic investigation Arup Mistri | Usha Kumari | Swati Mittal | Ajay Kumar Mittal 1 Skin Physiology Laboratory, Centre of Advanced Study, Department of Zoology, Institute of Science, Banaras Hindu University, Varanasi, Uttar Pradesh, 221 005, India Correspondence Swati Mittal, Skin Physiology Laboratory, Centre of Advanced Study, Department of Zoology, Institute of Science, Banaras Hindu University, Varanasi, 221 005, India. Email: drsmittal73@gmail.com Present addresses Usha Kumari, Assistant Professor, Zoology Section, Mahila Mahavidyalaya, Banaras Hindu University, Varanasi, 221 005, India Ajay Kumar Mittal, Retired Professor and Former Head of the Department of Zoology, Banaras Hindu University, 9, Mani Nagar, Kandawa, Near Chitaipur Crossing, Varanasi, 221106, India Funding information University Grants Commission, Grant/ Award Numbers: F1-17.1/2013-14/RGNF- 2013-14-SC-WES-36992 Review Editor: Prof. Paul Verkade Abstract The present work was undertaken with the aim to deduce morphological adaptations in skin of an angler catfish Chaca chaca by means of scanning electron microscopy. The fish is nocturnal, bottom dwelling, sluggish, ambush predator, lives in sand, mud, or soft substrates often buried and camou- flaged for protection and to feed. The surface of the epidermis is covered with polygonal epithelial cells, each having surface relief of microridges forming intricate patterns. In between epithelial cells irregularly distributed mucous cell openings, randomly distributed epidermal specialized structures, taste buds, and neuromasts are discernible. The epidermal specialized structures are keratinized. These are either irregularly the rounded elevated plaque like or the cone shaped structures. The superficial keratinized cells could frequently be discernible exfoliated at the surface. At intervals, characteristic epidermal projections could be observed. Surface of these projections at intervals is differentiated into short stumpy protuberances, each bearing a taste bud at its summit. Further, near the basal portion of these epidermal projections, conical, or rounded plaque like epidermal specialized structures are also discernible. The surface sculpture of the skin of Chaca chaca is asso- ciated with the structural and functional significance and physiological adaptations of the epidermis with respect to its ecological niche. KEYWORDS Chaca chaca, epidermis, SEM, surface organization 1 | INTRODUCTION Fish skin is involved in providing protection against physical and chemi- cal agents as well as pathogens in the external hostile environment. As the external organs are in direct contact with the environment, ultra- structural, and cytohistochemical characteristics of skin of healthy fish can be used as comparative controls to stress responses in aquaculture and natural systems (Arellano, Storch, & Sarasquete, 2004). A review of literature reveals a wealth of work on histological, histochemical, and functional aspects of fish skin (for review of literature see Arellano et al., 2004; Chang & Hwang, 2011; Glover, Bucking, & Wood, 2013; Guerra et al., 2006; Mittal & Banerjee, 1980; Mittal, Ueda, Fujimori, & Yamada, 1994a,b; Park, 2002; Saadatfar, Shahsavani, & Fatemi, 2010; Suzuki, 1992; Whitear, 1986; Zaccone, Kapoor, Fasulo, & Ainis, 2001; Zhang, Taniguchi, Takita, & Ali, 2003; Zhang, Deng, Zhang, Li, & Li, 2006). Nevertheless, information on the surface architecture of fish skin as seen under scanning electron microscope is, however, hitherto sporadic and scantly. Scanning electron microscopy provides a means for observing and surveying the details of surface architecture of tissues to an extent not possible by other procedures. Some of the articles on scanning electron microscopy of fish skin that deserve mention are of the authors who documented surface folds in superficial epidermal cells of three species of teleost fish (Hunter & Nayudu, 1978); 43 species of freshwater and marine teleosts (Fishelson, 1984) and unculi, an adaptive features of the epidermis of variety of Ostariophysan fishes (Roberts, 1982a). Whitear (1990) gave an account of causative aspects of microridges on the free surface of the superficial layer epithelial cells of several fish species. Whitear and Mittal (1986) investigated the skin of a teleost Agonus cataphractus by scanning electron microscopy. Mittal, Garg, and Microsc Res Tech. 2018;1–10. wileyonlinelibrary.com/journal/jemt V C 2018 Wiley Periodicals, Inc. | 1 Received: 25 October 2017 | Revised: 12 December 2017 | Accepted: 9 January 2018 DOI: 10.1002/jemt.22996