Vol.:(0123456789) 1 3 Environmental Science and Pollution Research https://doi.org/10.1007/s11356-022-24253-5 RESEARCH ARTICLE Immunoprotective role of aloin and disease resistance in Labeo rohita, infected with bacterial fsh pathogen, Aeromonas hydrophila Ayan Srivastava 1  · Usha Kumari 2  · Swati Mittal 3  · Ajay Kumar Mittal 4 Received: 19 July 2022 / Accepted: 13 November 2022 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2022 Abstract The efect of aloin on mucosal immune response and disease resistance was elucidated in Labeo rohita infected with the bacterial fsh pathogen, Aeromonas hydrophila. Fishes were divided into four groups: (i) control, (ii) vehicle control, (iii) bacteria infected and (iv) bacteria infected and aloin treated. Fish were intraperitoneally injected with A. hydrophila suspen- sion at the dose of 2 × 10 6  CFU/fsh at 0 day (d). Following bacterial injection at 0 d, fsh were treated with aloin at a dose of 1 mg/kg body weight intraperitoneally at an interval of 24 h for 4 consecutive days. Mucus collected from fsh of each group was analyzed at 2 d, 4 d, 6 d, 8 d and 10 d. In bacteria-infected fsh, a signifcant decrease (P < 0.05) in the activity of certain enzymatic and non-enzymatic immune parameters was observed. The activity of these immune parameters showed a gradual recovery on administration of aloin in bacteria-infected fsh. Cumulative mortality was also found to be low in the aloin-treated group as compared to that in the infected group. Thus, aloin could act as an immunostimulant and play a protective role against disease caused by bacteria. Keywords Labeo rohita · Aeromonas hydrophila · Mucus · Immune parameters · Disease resistance · Aloin Introduction Aeromonas hydrophila, an important bacterial pathogen iso- lated frequently from a wide variety of diseased freshwater fsh species, is responsible for several disease epidemics throughout the world that is a limiting factor in aquaculture production (Swain et al. 2010; Sahoo et al. 2011; Yilmaz et al. 2022). The bacterium has been associated with lesions on the body surface, tail and fn rot, haemorrhagic septi- caemia, epizootic ulcerative syndrome and necrosis in the kidney, spleen and liver in infected fsh species (Abd-El- Rhman 2009; Ardó et al. 2010; Crumlish et al. 2010; Hos- sain et al. 2011; Ramesh and Souissi 2018; Palanikani et al. 2020). It is extremely heterogeneous, and currently, there is no commercially available vaccine that is efective against A. hydrophila strains (Poobalane et al. 2008). The mucosal immune system of fshes is still poorly understood, and defined models for studying natural host–pathogen interactions are lacking. Mucosal tissues are points of contact between the host and environmental pathogens and are considered to be the main entry points for infection (Evenhuis and Cleveland 2012). Mucus has evolved to have a robust barrier mechanism that can trap and immobilize pathogens before they can contact epithelial Responsible Editor: Diane Purchase * Swati Mittal drsmittal73@gmail.com Ayan Srivastava ayan2025@gmail.com Usha Kumari usha.kanak@gmail.com Ajay Kumar Mittal profakmittal@gmail.com 1 Department of Zoology, MSM Samta College (BR Ambedkar Bihar University), Jandaha Road, Vaishali 844505, Bihar, India 2 Zoology Section, Mahila Mahavidyalaya, Banaras Hindu University, Varanasi 221005, Uttar Pradesh, India 3 Skin Physiology Laboratory, Centre of Advanced Study, Department of Zoology, Institute of Science, Banaras Hindu University, Varanasi 221005, Uttar Pradesh, India 4 Department of Zoology, Banaras Hindu University, 9, Mani Nagar, Kandawa, Near Chitaipur Crossing, Varanasi 221106, Uttar Pradesh, India