Elsevier

Fish & Shellfish Immunology

Volume 108, January 2021, Pages 53-62
Fish & Shellfish Immunology

Full length article
Dietary Azomite, a natural trace mineral complex, improved the growth, immunity response, intestine health and resistance against bacterial infection in largemouth bass (Micropterus salmoides)

https://doi.org/10.1016/j.fsi.2020.11.016Get rights and content

Highlights

  • The dietary supplementation of Azomite improved the growth and nutrient utilization of largemouth bass.

  • The efficiency of immune was enhanced by dietary Azomite.

  • Dietary Azomite promoted the resistance against Aeromonas hydrophila.

Abstract

Azomite is a hydrated calcium sodium aluminosilicat rich in rare earth elements. To investigate the dietary effects of Azomite on growth, intestine microbiota and morphology, immunohematological changes and disease resistance, seven diets with Azomite supplementation of 0 (the control), 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 g/kg (A0, A1, A2, A3, A4, A5, A6), were prepared and fed to largemouth bass, Micropterus salmoides (7.96 ± 0.19) for 60 days. The results revealed that the weight gain (WG) increased first and then decreased with the increasing dietary Azomite, and the A2 group presented the highest WG and lowest feed conversion ratio among all the groups. The supplementation of 2.0 g/kg Azomite significantly increased the intestine protease activity, the crude protein of whole body and protein retention (P < 0.05), and high inclusion of Azomite (6.0 g/kg) significantly reduced the lipid retention (P < 0.05). The amounts of red blood cells in A5, A6 groups, white blood cells in A3, A5, A6 groups and lymphocyte in A2-A6 groups were all significantly higher than those in the control group (P < 0.05). In addition, serum superoxide dismutase and catalase activities in A5, A6 groups, and serum alkaline phosphatase and lysozyme activities in A2-A4 groups showed significantly higher values than the control group (P < 0.05). Intestinal microbiota analysis indicated that the Tenericutes abundance was increased, whereas Proteobacteria abundance was decreased in all Azomite supplemented groups. The villus height in A2-A4 groups, and the villus width in A2 group were significantly higher than those of the control group (P < 0.05). The cumulative mortality was reduced by the addition of 2.0–5.0 g/kg Azomite after challenging with A. hydrophila (P < 0.05). In conclusion, proper addition of Azomite in diets improved the growth, intestine morphology, immune response and disease resistance in largemouth bass, and the optimal inclusion was estimated to be 2.0–3.0 g/kg diet.

Introduction

Largemouth bass (Micropterus salmoides) is an important freshwater carnivorous species native to North America [1]. Due to its rapid growth and tender flesh without intermuscular spines, largemouth bass has become one of the fastest growing farmed fish in China, and the culture production reached 477808 tons in 2019 (China Fishery Statistical Yearbook, 2020). However, diseases problems are becoming more and more serious in largemouth bass farming. Although antibiotics are generally successful in treating bacterial disease, the accumulation of antibiotics residues either in the environment or in fish tissues and the emergence of antimicrobial resistant strains are likely to cause human health problems, so the use of antibiotics is increasingly restricted [[2], [3], [4]]. It has become the focus of global aquaculture industry to use effective immune stimulants instead of antibiotics to improve resistance to diseases by enhancing innate immune mechanisms in aquatic animals [5].

Azomite is a hydrated calcium sodium aluminosilicate originating from a volcanic ash and an ancient seabed deposit with a large amount of plant and animal residues and minerals. Especially, it contains over 70 minerals and trace elements, including copper, iodine, iron, magnesium, manganese, selenium, zinc and some rare earths, such as lanthanum, cerium and rubidium [6], and it has been used as a soil re-mineralizer for plants and feed additive for animals. Trace minerals are known as crucial component of hormones and enzymes, which serve as cofactors and activators of numerous enzymes, as well as take part in widely variety of biological processes [7]. Integrating trace minerals into feeds has important roles in protein synthesis, nutrients digestion, feed utilization and immune response [8]. Organic Materials Review Institute (OMRI, Eugene, OR, USA) has approved Azomite as a natural mineral that can be used in organic agriculture. Emerson and Hooge [9] summarized 13 experiments concerning Azomite in chicken production and found that adding 3–5 g/kg Azomite to the diet improved breast meat yield from 17.9% to 18.7%. Mattewset et al. [10] reported that dietary Azomite (5.0 g/kg) improved pork quality score as color in finishing pig. In aquaculture, dietary Azomite has been reported to promote the growth performance of tilapia (Oreochromis niloticus aureus) [11,12], catfish (Pangasius hypophthalmus) [13], enhance the digestive enzymes activities and non-specific immune function in grass carp (Ctenopharyngodon idellus) [14], white shrimp (Litopenaeus vannamei) [15], koi carp (Ciprinus carpio) [16], tilapia and shrimp [17], and improve the disease resistance in tilapia [18] and white shrimp [15]. Besides, rare earth minerals have been demonstrated some antibacterial properties [19,20] and can stimulate the digestive micro-organism or enzymes and increase the proteolytic activities [[21], [22], [23]].

Since 2020, the use of antibiotics as additives in feed has been strictly banned in China [24]. Therefore, it is particularly urgent to find green additives for promoting growth and health of cultured animals. Based on the results from other animals, Azomite was expected to have the ability to improve the growth, immune function and disease resistance of largemouth bass. Besides, no investigation has been conducted to exploit the potential efficacy of Azomite on intestine microbiota in fish. So, this study was conducted to evaluate the effects of dietary Azomite on growth performance, body composition, immune response, intestine health, resistance against A. hydrophila infection in largemouth bass.

Section snippets

Ethical statement

All procedures of fish manipulation were observed the criterions and recommendations established by Ministry of Science and Technology of the People's Republic of China for care and use of scientific animals (Publication No.85–23, revised 1985). All experimental animal care protocols were approved by the Institutional Animal Care and Use Committee (IACUC) of Shanghai Ocean University (Shanghai, China).

Experimental diets and design

Seven diets were formulated by adding Azomite into basal diet at levels of 0 g/kg (control

Growth performance and morphometric parameters

As shown in Table 2, no mortality was recorded during the feeding period. Fish fed 2.0 g/kg Azomite diet showed the highest WG, SGR and lowest FCR among all the groups. Compared to the control group, the WG of 2.0 g/kg Azomite group was increased by 11.2% (P < 0.05), while FCR was decreased by 0.1 (P < 0.05). WG tended to increase in 1.0, 3.0, 4.0 and 5.0 g/kg Azomite groups, while decrease in 6.0 g/kg Azomite group (P > 0.05). CF was increased in 3.0 and 4.0 g/kg Azomite groups (P < 0.05), and

Growth performance and feed utilization

Azomite is a natural mineral product with a broad spectrum of over 70 minerals and trace elements, which may play important roles in the physiology of organisms and positively affect the growth performance of animals. A study by Liu et al. [11] showed that weight gain was increased by 12.7% and 9.9% by adding 2.5 and 5.0 g/kg Azomite in diet of tilapia. In grass carp [14] and white shrimp [15], the dietary supplementation of 2.0 g/kg Azomite enhanced the growth performance and feed utilization.

Conclusion

In summary, the appropriate addition of Azomite in the diet is beneficial for fish by improving the growth performance, feed utilization, non-specific immune function, intestinal morphology and resistance against A. hydrophila in largemouth bass. The proper inclusion of Azomite is suggested to be 2.0–3.0 g/kg of diet.

Declaration of competing interest

The authors declare no conflict of interest.

CRediT authorship contribution statement

Xiaoying Xu: Project administration, Data curation, Formal analysis, Methodology, Software, Writing - original draft. Xiaoqin Li: Funding acquisition, Conceptualization, Investigation, Writing - review & editing. Zhen Xu: Methodology, Formal analysis, Validation. Wenxiang Yao: Methodology, Formal analysis, Validation. Xiangjun Leng: Funding acquisition, Conceptualization, Investigation, Writing - review & editing.

Acknowledgements

This work was financially supported by the grants from Shanghai Lytone Biochemicals, Ltd. (Shanghai, China).

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    The first author is Xiaoying Xu, and the co-first author is Xiaoqin Li. Both authors contributed equally to this work.

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