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Frontiers in Veterinary Science
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This study evaluated the immunotoxic effects of thallium (Tl) in Nile tilapia fingerlings
and the recovery role of dietary Astragalus membranaceus polysaccharides (ASs). An
8-week experiment was designed where 180 fishes were randomly and equally assigned
in triplicates into the six groups: the control group (CNT) was reared in unpolluted
water and fed a commercial diet, two groups were fed a well-balanced commercial
diet plus 1.5 and 3.0 g AS/kg diet (AS0.15 and AS0.30), respectively, the fourth group
was exposed to a sublethal dose of Tl (41.9 μg l−1) [equal to 1/10 of 96-h lethal
concentration 50 (LC50)], and the last two groups were fed 0.15 and 0.3% AS,
respectively, and concurrently exposed to Tl (41.9 μg l−1) (AS0.15+Tl and AS0.30+Tl).
Fish hematobiochemical parameters, serum immunity [nitric oxide, total immunoglobulin
M (IgM) levels, and lysozyme activity], transcription of hepatic interferon-g (IFN-g),
interleukin-1b (IL-1b), and tumor necrosis factor-a (TNF-a), and resistance to Aeromonas
hydrophila (A. hydrophila) were assessed. Hematobiochemical parameters and serum
immune indices were significantly decreased in the fish group exposed to sublethal
Tl concentration compared to the CNT group. Furthermore, Tl exposure significantly
induced overexpression of IL-1b, TNF-a, and IFN-g genes (4.22-, 5.45-, and 4.57-fold
higher, respectively) compared to CNT values. Tl exposure also increased the cumulative
mortality (%) in Nile tilapia challenged with A. hydrophila. Remarkably, the groups fed
AS0.15+Tl and AS0.30+Tl significantly ameliorated all the aforementioned parameters,
but did not reach CNT values. Our findings suggest the possible immunomodulating roles
of dietary AS in recovering the immunotoxic effects of Tl in Nile tilapia. We can conclude
that dietary AS would be useful for maintaining the immunity of Nile tilapia fingerlings.
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