Protective efficacy of Azomite enriched diet in Oreochromis mossambicus against Aeromonas hydrophila

Abstract

The effect of dietary supplementation with Azomite, a natural mineral of volcanic ash, on growth performance, innate immune response, and disease resistance in Oreochromis mossambicus against Aeromonas hydrophila is reported. On being fed with 4gkg−1 and 6gkg−1 enriched diets in infected fish the survival rate, weight gain (WG), protein efficiency ratio (PER),specific growth rate (SGR), feed conversion rate (FCR), and feed efficiency (FE) increased significantly from weeks 1 to 4; the complement activity registered a significant increase from weeks 1 to 4; however the phagocytic activity increased significantly between weeks 2 and 4. With any supplementation diet the respiratory burst activity significantly increased between weeks 2 and 4. The lysozyme activity significantly increased the infected fish fed with 4gkg−1 and 6gkg−1 Azomite diets from weeks 1 to 4. The cumulative mortality was lower in fish fed with 4gkg−1 and 6gkg−1diets (10% and 15%) than with2gkg−1diet (20%). The present results suggest that Azomite enriched diet at 4gkg−1 and 6gkg−1positively enhance the innate immunity and disease resistance in O. mossambicus against A. hydrophila. Statement of relevanceAeromonas hydrophila is one among the most common bacterial pathogens in freshwater habitats throughout the world (Larsen and Jensen, 1977) affecting fish species including carps both in farms and field. The traditional use of chemotherapeutics and antibiotics to combat fish disease has the risk of generating resistant pathogens, alter gut microbiota, bioaccumulation, and environmental pollution. Commercial vaccines are expensive for fish farming practices and are specific against particular pathogens. Azomite is a mineral ore that occurs in natural state prior to being ground is the registered trademark for a complex silica ore (hydrated sodium calcium aluminosilicate, HSCAS) and contains over 70 minerals and trace rare elements, including calcium, phosphorus, magnesium, iron, selenium, copper, zinc, and manganese. Undersea volcanic sediment of Azomite was mixed with a large amount of plant and animal residues and minerals. It was especially rich in rare earth elements. The growth performance was enhanced with dietary supplementation of rare earth elements at low concentrations in various farming animals, including beef cattle, sheep, pigs, rabbits, ducks, chickens, shrimps, and fish (Shen et al., 1991; Rosewell, 1995; Duan et al., 1998; Tang et al., 1998; Liu, 2005; Yang and Chen, 2000; Yang et al., 2005). Dietary supplementation of rare earth elements in aquaculture increases in output and survival rate of several fish species including grass carp, blunt-snoup carp, black carp, common carp, silver carp, and prawn (Tang et al., 1998; Tang et al., 1997). Liu et al. (2009) have been reported that 2.5 and 5.0gkg-1 Azomite supplementation in the diets improve the growth, pepsin activity, and nutrient digestibility in tilapia (Oreochromis niloticus × O. aureus). Dietary supplementation with 2.0gkg-1 Azomite in grass carp (Ctenopharyngodon idellus) improved the efficiency of feed utilization, activities of intestinal digestive enzymes, and serum non-specific immune function (Liu et al., 2011). Based on the above information, Azomite was anticipated to have the ability to promote growth, innate immune function, and disease resistance in fish culture. So far, there was no study reported on the impact of Azomite on innate immune response and diseases resistance in fish against bacterial diseases. Therefore, the present study investigated dietary supplementation with Azomite on growth performance, innate immune response, and disease resistance in Oreochromis mossambicus against A. hydrophila.