Effects of dietary supplementation with apple peel powder on the growth, blood and liver parameters, and transcriptome of genetically improved farmed tilapia (GIFT, Oreochromis niloticus).

Jun Qiang,Yi Fan Tao,Pao Xu,Zhe Ming Cao,Omyia Ahmed Mohamed Khamis,Jie He,Huo Jin Jiang,Jin Wen Bao,Juan J Loor

doi:10.1371/journal.pone.0224995

Jun Qiang, Yi Fan Tao + Show 7 more

Open Access

https://doi.org/10.1371/journal.pone.0224995

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Abstract

High-density aquaculture and nutritional imbalances may promote fatty liver in genetically improved farmed tilapia (GIFT, Oreochromis niloticus), thus reducing the gains achieved by breeding. In this study, apple peel powder (APP) was used as a feed additive for GIFT. A control group (fed on a diet without APP) and five groups fed on diets supplemented with APP (at 0.05%, 0.1%, 0.2%, 0.4%, or 0.8% of the diet, by weight) were established to investigate the effects of APP on GIFT growth performance and physiological parameters, and on gene expression as determined by transcriptomic analysis. Dietary supplementation with APP at 0.2% promoted GIFT growth, reduced total cholesterol and triacylglycerol levels in the serum and liver, and decreased alanine aminotransferase and aspartate aminotransferase activities in the serum. Gene expression profiles in the liver were compared among the control, 0.2% APP, and 0.8% APP groups, and differentially expressed genes among these groups were identified. Annotation analyses using tools at the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases showed that the differentially expressed genes were mainly involved in the regulation of immunity and fat metabolism. The results showed that excessive supplementation with APP in the diet significantly inhibited the expression of insulin-like growth factor 2 and liver-type fatty acid-binding protein, and stimulated the expression of fatty acid desaturase 2, heat shock protein 90 beta family member 1, and nuclear factor kappa B. This resulted in disordered lipid metabolism and increased pro-inflammatory reactions, which in turn caused liver damage. Therefore, APP has good potential as an environmentally friendly feed additive for GIFT at levels of 0.1%–0.2% in the diet, but excessive amounts can have adverse effects.

Highlights

The use of immunostimulants in aquafeeds improves the defense responses of fish when they are exposed to pathogens, and provides an alternative to antibiotics and chemotherapeutics for treating fish diseases [1,2,3,4]
The weight gain (WG) and specific growth rate (SGR) were significantly lower in 0.4%–0.8% apple peel powder (APP) groups than in the control group and the 0.05%–0.2% APP groups (P
The broken-line regression model of SGR indicated that 0.17% APP was the optimal amount for GIFT to achieve optimal growth (Fig 1)

Summary

Introduction

The use of immunostimulants in aquafeeds improves the defense responses of fish when they are exposed to pathogens, and provides an alternative to antibiotics and chemotherapeutics for treating fish diseases [1,2,3,4]. Food waste has traditionally been viewed as an undesirable material to be disposed of, at considerable expense, via landfill or incineration, or used as animal feed. Such wastes are increasingly considered to be a promising source of valuable nutraceuticals [5,6]. Apple peel extract (APE) was shown to have an inhibitory effect on insulin resistance-related obesity and type II diabetes in mice fed on a high-fat diet [9] In those mice, dietary supplementation with APE resulted in significantly improved glucose tolerance and insulin sensitivity, reduced cytokine levels in the early phase of pro-inflammation, and decreased oxidation levels in adipose tissue [9]. Li et al [10] found that hyperlipidic mice fed on a diet supplemented with 4% apple dietary fiber showed significant reductions in blood glucose and blood fat

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