Evaluation of nano-ZnOs as a novel Zn source for marine fish: importance of digestive physiology

2017-10-20T08:09:04Z (GMT) by Jian Wang Aili Wang Wen-Xiong Wang
<p>Waterborne nanotoxicology of zinc oxide nanoparticles (nano-ZnOs) has been extensively studied over the past decade, whereas their potential dietary toxicity and applications were seldom investigated. In the present study, we systematically investigated both short-term bioavailability and chronic effects of nano-ZnOs to two marine fish (marine medaka <i>Oryzias melastigma</i> and red drum <i>Sciaenops ocellatus</i>). At normal supplementary level (80 mg Zn/kg), red drum (with a stomach) had similar assimilation efficiencies of nano-ZnOs and ZnCl<sub>2</sub>. Correspondingly, <i>in vitro</i> digestion experiments showed the continuous dissolution of nano-ZnOs in acid environment. In contrast, nano-ZnOs were more bioavailable than ZnCl<sub>2</sub> to medaka (stomach-less) at 80 mg Zn/kg supplementary level. There results were further validated by using bulk-ZnOs. Chronic dietary exposure to nano-ZnOs (80 mg/kg) significantly enhanced the antioxidative defenses in medaka, with no negative effect on fish growth. Beneficial effects disappeared in the high dietary nano-ZnOs (300 mg/kg) treatment. For the first time, we provided direct evidence that nano-ZnOs was more bioavailable than ZnCl<sub>2</sub> and bulk-ZnOs to stomach-less fish at normal dietary Zn inclusion level (<80 mg/kg), with potential benefits on antioxidative defenses. It is also necessary to pay attention to the dietary nano-ZnOs toxicity on stomach-less fish due to the presence of real ‘nano-effects.’</p>