Indian lotus, Nelumbo nucifera (Gaertn.) is a valued medicinal plant that exhibits several pharmacological properties. The present work aimed to investigate the effect of Indian lotus as a feed supplement on the growth performance, haematological and biochemical indices, and intestinal histo‐morphology of Nile tilapia (Oreochromis niloticus L.). The fish were randomly distributed into four groups and fed on a basal diet containing Indian lotus leaf powder at different concentrations (0, 0.1, 0.2 and 0.4%) for up to 60 days. The results elucidated that Indian lotus supplemented diets (0.2% and 0.4% followed by 0.1%) significantly improved weight gain, specific growth rate (%) and feed conversion ratio (p < .05). The feed intake was significantly increased in the fish fed on the Indian lotus supplemented diets in a dose‐dependent manner (p < .05). However, Indian lotus had no significant effect (p > .05) on survival rate, total erythrocytes (RBCs) count, haemoglobin (Hb) and hematocrit value (PCV, %) except a significant reduction on Hb content of the fish fed on 0.2% Indian lotus and a significant increase in PCV (%) in the fish fed on 0.1% Indian lotus (p < .05). The total leucocytes (WBCs), neutrophils and lymphocytes counts displayed significant elevations in the fish fed on the Indian lotus diets especially at 0.2% and 0.4%, whereas significant reduction in neutrophils count in the fish fed on 0.1% Indian lotus (p < .05) was observed. The serum glucose was significantly decreased in the fish fed on Indian lotus (0.1% and 0.2%), whereas cholesterol and triglycerides were markedly increased in the fish fed on the Indian lotus supplemented diets (p < .05). Moreover, the intestinal villous heights and the numbers of goblet cells and intraepithelial lymphocytes (IEL) were significantly boosted in all parts of the intestine in all Indian lotus diet groups as compared with the control group. However, as an exception, villous heights in the middle part of the intestine in the fish fed on 0.1% and 0.4% diets (p < .05) were not affected. In the proximal part, the villous heights and the numbers of goblet cells were markedly increased in fish fed on 0.2% and 0.4% diets followed by 0.1% diet. The fish fed on 0.2% lotus supplemented diet followed by 0.1% and 0.4% supplemented diets exhibited significant elevations in villous heights in the distal part and the numbers of goblet cells in the middle part of the intestine. There were no significant differences between the fish fed on the supplemented diets in the numbers of goblet cells in the distal part and the numbers of IEL in the proximal and middle parts (p > .05). In the distal part, the numbers of IEL revealed a significant elevation in 0.4% lotus supplemented diet followed by 0.1% and 0.2% lotus supplemented diet groups (p < .05). Therefore, this study indicates the advantageous effect of the Indian lotus leaves as a natural feed additive for improving growth, intestinal structure and hence, health status of Nile tilapia.

This study assessed the immune response of Nile tilapia (Oreochromis niloticus L.) after feeding on different levels (0.1%, 0.2% and 0.4%) of dietary Indian lotus (Nelumbo nucifera) leaf powder for 45 days. We evaluated both the nonspecific immune response at the end of the feeding period and the resistance to Aeromonas hydrophila. Exposure to Indian lotus resulted in a significant elevation in serum total globulins, serum lysozyme activity, serum killing percentage and the phagocytic activity (p < 0.05). Total serum protein and albumin showed no remarkable variation between tilapia fed on 0.1% Indian lotus and the control group (p > 0.05). In addition, the relative expressions of immune-related genes, namely interleukin-1β and tumour necrosis factor-α were significantly up-regulated in tilapia fed on 0.4% Indian lotus as compared to the control group; their expressions were down-regulated in the other tested groups (p < 0.05). The survival rate of Nile tilapia postchallenge to A. hydrophila reported a significant and dose-dependent increase in the Indian lotus-supplemented groups (p < 0.05). Therefore, dietary incorporation of Indian lotus leaves (0.4%, 0.2% and 0.1%) could strengthen the immunity of Nile tilapia and improve its resistance to A. hydrophila infection. Therefore, Indian lotus leaves could serve as potential feed supplements for Nile tilapia. K E Y W O R D SAeromonas hydrophila, Indian lotus, interleukin-1β, Nile tilapia, tumour necrosis factor-α

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Aquaculture has become a worldwide economically important industry which requires continuing research with scientific and technical developments and innovations (Bektaş et al., 2017).To cover the increasing need of food in the World, an intensive production in fisheries has been a must which ended with the occurrence of diseases (FAO, 2016). The fact that aquaculture sector is the fastest growing food-production industry in the world is plagued by diseases. The annual economic loss in the aquaculture industry due to diseases is estimated to be billions of US dollars worldwide (Klesius and Pridgeon, 2011). The development of intensive aquaculture has led to the emergence of various bacterial diseases (Pridgeon and Klesius, 2012). Infectious disease outbreaks in fish farms might be caused by single or multiple pathogens; however, little is known about the association of different microorganisms causing coinfections and its consequences (Dong et al., 2015a , 2015b).

The influences of Boswellia serrata resin extract (BSRE) as a feed additive on the growth performance, immune response, antioxidant status, and disease resistance of Nile tilapia, Oreochromis niloticus L. were assessed. One hundred-forty four fingerlings (initial weight: 21.82 ± 0.48 g) were randomly allotted into four groups with three replicates where they were fed on one of four treatments with four levels of Boswellia serrata resin extract 0, 5, 10, or 15 g kg−1, BSRE0, BSRE5, BSRE10, BSRE15, respectively for eight weeks. After the end of the feeding trial, the fish were challenged with Staphylococcus aureus, and mortalities were noted. The final body weight, total body weight gain, and the total feed intake were quadratically increased in BSRE5 treatment (p < 0.01). The protein productive efficiency (PPE) was linearly and quadratically increased in all BSRE supplemented treatments (p < 0.01). Dietary addition of BSRE raised the fish crude protein content and reduced the fat content in a level-dependent manner (p < 0.01). The ash content was raised in the BSRE15 group (p < 0.01). Dietary BSRE supplementation decreased the serum levels of glucose, total cholesterol, triglycerides, and nitric oxide. It increased the serum levels of total protein, albumin, total globulins, α1 globulin, α2 globulin, ß globulin, ɣ globulin, Catalase, and SOD (superoxide dismutase) activity, GSH (reduced glutathione), lysozyme activity, and MPO (myeloperoxidase) in a level-dependent manner (p < 0.05). The BSRE15 diet increased the serum level of ALT (alanine aminotransferase) and decreased creatinine serum level (p < 0.05). Dietary BSRE supplementation increased the relative percentage of survival % (RPS) of S. aureus challenged fish. The histoarchitecture of the gills and kidney was normal in the BSRE5 treatment and moderately changed in BSRE10 and BSRE15 treatments. The splenic lymphoid elements were more prevalent, and the melano-macrophage centers (MMC) were mild to somewhat activated in BSRE supplemented treatments. Dietary BSRE supplementation improved the intestinal histomorphology. It can be concluded that BSRE addition can enhance the antioxidant activity, immune status, and disease resistance of O. niloticus to S. aureus infection. The level of 5 g kg−1 BSRE can improve fish growth without causing harmful effects on fish health. The highest levels of BSRE are not recommended as they badly affected the histoarchitecture of many vital organs.