Abstract
Assessing the availability of dietary micro-minerals is a major challenge in mineral nutrition of fish species. The present article aims to describe a systematic approach combining different methodologies to assess the availability of zinc (Zn) in Atlantic salmon (Salmo salar). Considering that several Zn chemical species can be present in an Atlantic salmon feed, it was hypothesised that Zn availability is influenced by the Zn chemical species present in the feed. Thus, in this study, the first protocol is about how to extract the different Zn chemical species from the feed and to analyze them by a size exclusion chromatography-inductively coupled plasma mass spectroscopy (SEC-ICP-MS) method. Subsequently, an in vitro method was developed to evaluate the solubility of dietary Zn in Atlantic salmon feeds. The third protocol describes the method to study the impact of changing Zn chemical species composition on the uptake of Zn in a fish intestinal epithelial model using a rainbow trout gut cell line (RTgutGC). Together, the findings from the in vitro methods were compared with an in vivo study examining the apparent availability of inorganic and organic sources of Zn supplemented to Atlantic salmon feeds. The results showed that several Zn chemical species can be found in feeds and the efficiency of an organic Zn source depends very much on the amino acid ligand used to chelate Zn. The findings of the in vitro methods had less correlation with that outcome of the in vivo study. Nevertheless, in vitro protocols described in this article provided crucial information regarding Zn availability and its assessment in fish feeds.
Highlights
Fish meal and fish oil were traditionally used in Atlantic salmon feed
The use of the protocols described in this article allowed the sequentially study of the chemical and biological aspects underlying the 'availability' of Zn in Atlantic salmon
This study reported the use of a Zn speciation analysis method
Summary
Fish meal and fish oil were traditionally used in Atlantic salmon feed. The aforementioned shift in feed composition has resulted in low dietary availability and an increased need for improving mineral availability in Atlantic salmon feeds, especially zinc (Zn)[2 ]. The reduced availability might be a result of a change in the Zn level, Zn chemical species or/and antinutritional factors present in the feed matrix. In this scenario, a new array of additives generically considered as 'organic sources' have emerged with potential of being a better available source of dietary minerals to fish. 1. Evaluation of Zn chemical species in the soluble fraction of an Atlantic salmon feed using a SEC-ICP-MS method. Adjust the pH of the solution to pH 8.5 with HCl solution, monitoring the pH change with a pH meter
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