Abstract
This study investigated the effects of dietary Flos populi extract (FPE) on the growth, antioxidation capability, innate immune response, and disease resistance in gibel carp. A total of 480 fish were fed with five different diets containing 0, 0.5, 1.0, 1.5, or 2.0 g kg−1 FPE (designated as control, D0.5, D1.0, D1.5, or D2.0 groups) for 45 days. The fish were challenged with A. hydrophila after the feeding trial. Compared with the control, the feed efficiency (FE), weight gain (WG), final body weight (FBW), and specific growth rate (SGR) were significantly improved in groups D1.0 and D1.5. Dietary FPE significantly increased serum superoxide dismutase (SOD), glutathione peroxidase (GPx), and catalase (CAT) activities, as well as glutathione (GSH) content. The contents of protein carbonyl (PCC) and malondialdehyde (MDA) in serum decreased significantly. Additionally, FPE supplementation in diets resulted in significant improvement in serum lysozyme (LZM) and myeloperoxidase (MPO) activities, as well as immunoglobulin M (IgM) and complement 3 (C3) concentrations. The hepatic antioxidant enzymes (CAT and SOD) activities increased, whereas content of MDA decreased in fish treated with dietary FPE than those of control both pre- and post-challenged. After 12 h-challenge, an obvious downregulation of hepatic Kelch-like-ECH-associated protein 1 (Keap1), splenic tumor necrosis factor-α (TNF-α), interleukin (IL)-8, IL-1β, and toll-like receptor 2 (TLR2) mRNA levels was observed in fish treated with dietary FPE, whereas hepatic Nrf2 transcription level was upregulated compared to the control. Furthermore, compared to group D0.5, higher relative percent survival (RPS) was observed in gibel carp fed dietary 1.0–2.0 g/kg FPE. Our results reveal that FPE supplemented diet has a stimulatory effect on antioxidant capacity and nonspecific immune response, along with improved growth performance and enhanced resistance against A. hydrophila infection in juvenile gibel carp.
Highlights
Gibel carp (Carassius auratus gibelio) is considered one of the most important cultivated freshwater fish species in China
Our results reveal that Flos populi extract (FPE) supplemented diet has a stimulatory effect on antioxidant capacity and nonspecific immune response, along with improved growth performance and enhanced resistance against A. hydrophila infection in juvenile gibel carp
No significant difference (P > 0.05) of FI and PRE in gibel carp was found among the five groups
Summary
Gibel carp (Carassius auratus gibelio) is considered one of the most important cultivated freshwater fish species in China. The rapid expansion of its production has brought about many serious problems, e.g., the development of the highdensity culture and lack of the efficiency disease prevention strategy As a result, such intensification may cause stressful conditions, which suppress the immune system, along with increase the susceptibility of fish to infectious diseases (Lueke et al 2019; Harikrishnan et al 2011; Cabello 2004). Fish are often challenged by various stressors, which are originated from environmental changes and human activities (Conte 2004) These stressors result in poor antioxidation capability and lower immunity of gibel carp, leading to breeding failure and even catastrophic economic loss (Abdel-Tawwab et al 2020). Plant-derived supplements are used as exogenous antioxidants and immunoprophylactics in aquaculture (Tan et al 2018; Harikrishnan et al 2011; Hai 2015)
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