CCD and RSM optimization approach for antioxidative activity and immune regulation in head kidney of yellow catfish (Pelteobagrus fulvidraco) based on different lipid levels and temperatures

Highlights

• Optimization is used by the response surface method and central composite design.

• Temperature or lipid diet markedly mediates on oxidative and immune regulation.

• Quadratic effect of temperature or lipid diet notably affects oxidation and immunity.

• High temperature-high lipid diet markedly inhibit antioxidative and immune response.

• Optimal temperature/lipid diet (26.9°C/7.7%) stimulates immune regulation.

Abstract

Yellow catfish (Pelteobagrus fulvidraco) is an important economic cultured fish in China. Here we report antioxidative activity and immune regulation in head kidney using a central composite design based on water temperature (20–34 °C) and dietary lipid (2–17%). Response values were optimized using response surface methodology to maximize the immune response and relieve oxidative stress. The experiment was conducted under laboratory conditions and lasted for seven weeks. The results showed that the linear effects of lipid level on superoxide dismutase (SOD, and lysozyme (LYZ) activity, and malondialdehyde (MDA) content in head kidney, respiratory burst activity (RBA) of head kidney macrophages, and cumulative mortality of fish infected by Streptococcus iniae (S. iniae) were significant (P < 0.05). Similarly, the linear effects of water temperature on SOD activity, MDA content, and cumulative mortality were significant (P < 0.05). In addition, the quadratic effects of water temperature and lipid level on all experimental response values were significant (P < 0.05), and no interactive effect was found between water temperature and lipid level (P > 0.05). High water temperature and high lipid diet significantly reduced the antioxidative activity and immune response in head kidney, and increased MDA content, which caused increased mortality of the S. iniae-infected fish. The adjusted R² values for SOD activity, MDA content, LYZ activity, RBA, phagocytic activity, and cumulative mortality regression models were 0.76, 0.85, 0.87, 0.79, 0.64, and 0.87, respectively. The optimal combination of water temperature and lipid level was 26.9 °C and 7.7%, at which good antioxidative activity and immune regulation were achieved, with reliability of 0.878. This combination was close to the optimal combination of water temperature and lipid level for growth performance (27.5 °C and 9.2%) reported previously. Thus, the optimal combination may not only promote growth, but also enhance antioxidant and immune levels.

Introduction

Head kidney is not only an important hematopoietic tissue in fish, but is also important for the occurrence, differentiation, and proliferation of immune cells such as macrophages, granulocytes, and lymphocytes [1], [2]. Head kidney is extremely sensitive to changes in the external environment, and therefore has been used as an important target organ for stress response and environmental monitoring [3], [4]. Previous studies have found that the stress response can cause significant increases in plasma cortisol levels, can regulate phagocytic activity (PA) as well as the number of phagocytic cells of head kidney, and suppress a variety of immune functions. For example, acute low temperature stress (9 °C) caused a significant decrease in the number of kidney granulocytes in common carp (Cyprinus carpio) [5]. Transport and confinement stresses inhibited the respiratory burst activity (RBA) of head kidney phagocytic cells and cytotoxicity of eosinophils in the abdominal cavity in sea bass (Dicentrarchus labrax) [6]. High temperature stress inhibited the RBA of phagocytic cells in head kidney of Japanese medaka (Oryzias latipes) [7]. Additionally, 2-h short-term crowding stress inhibited the PA of head kidney leukocytes in gilthead seabream (Sparus aurata), but had no effect on RBA [8]. Li et al. [9], [10] found that chronic or acute ammonia nitrogen stress reduced lysozyme (LYZ) activity in yellow catfish (Pseudobagrus fulvidraco), and inhibited the PA and RBA of head kidney macrophages. Sea lice (Lepeophtheirus salmonis) parasitic on Atlantic salmon (Salmo salar L.) caused significantly increased plasma cortisol levels in the host, and the PA and RBA in head kidney macrophages were significantly decreased [11].

Nutritional intervention in fish can stimulate or inhibit the immune activity of head kidney, and regulate antioxidant capacity. For example, Wu and Chen [12] found that phagocytosis and RBA in head kidney of the juvenile grouper Epinephelus malabaricus increased with an increased ratio of linolenic acid tolinoleic acid (from 0.4 to 3.3) in feed. The supplementation of 0.04% glycyrrhizic acid in the diet significantly increased the PA of the macrophages in large yellow croaker (Larimichthys crocea) [13]. Additionally, dietary arginine or isoleucine stimulated the immune response of Jian carp, and regulated the antioxidant status and cytokines of head kidney [14], [15]. In head kidney macrophages isolated from large yellow croaker, high concentrations of eicosapentaenoic acid (200 and 1000 μM) significantly inhibited the percentage of phagocytosis in macrophages and increased the malondialdehyde (MDA) content [16]. Lack or excess of dietary lipid reduced the RBA of head kidney leukocytes in largemouth bass (Micropterus salmoides) and grouper [17], [18], inhibited the activity of antioxidant enzymes and expression of immune genes, and caused oxidative damage and apoptosis in grass carp (Ctenopharyngodon idella) [19].

Yellow catfish is an important economic cultured fish in China. It is distributed widely in the Yangtze River and the Pearl River. The muscle of yellow catfish contains many essential amino acids and has the advantage of no muscular spines, which has been well received by consumers. According to the data published in the “China Statistical Yearbook 2016”, in 2015, yellow catfish production in China reached 355.725 million tons, an annual increase of more than 15%, making yellow catfish one of the major freshwater aquaculture species [20]. Water temperature is an important environmental factor for fishes. Appropriate water temperature can promote the digestion, absorption, and utilization of dietary nutrients, to maximize fish growth [21]. In a previous study, we used a central composite experiment design (CCD) with response surface methodology (RSM) to study the water temperature and dietary lipid for yellow catfish, and established the optimal combination for growth and feed efficiency [22]. Whether the same optimal combination can help to improve the immune and antioxidant capacity of yellow catfish is the main problem explored in this study.

First, we assumed that an optimal combination of water temperature and dietary lipid would help to improve the antioxidant status and immunological activity in head kidney. To verify this hypothesis, we used a CCD to study superoxide dismutase (SOD) and LYZ activity as well as MDA content in the head kidney of yellow catfish under different water temperature–dietary lipid combinations. Macrophages were isolated from head kidney, and the PA and RBA of the macrophages were measured. Finally, the cumulative mortality of fish was assessed after infection with the exogenous bacteria Streptococcus iniae (S.iniae). Multiple experimental results were optimized simultaneously using RSM. The results of this study will provide a reference for optimizing the culture conditions of yellow catfish, and promote healthy and efficient culture. This study is of significance in achieving cross-disciplinary applications.