溶氧和饲料脂肪水平的交互作用对罗非鱼生理机能的影响

Effects of the interaction between dissolved oxygen content and lipid level on the physiological functions of Nile tilapia

中文关键词: 罗非鱼  溶氧  脂肪水平  交互作用  肝功能  免疫指标

英文关键词: Oreochromis niloticus  Dissolved oxygen  Fat level  Interaction  Liver function  Immune index

中文摘要:

      本研究旨在探究溶氧含量和脂肪水平的交互作用对罗非鱼的生长性能、肝脏抗氧化能力、免疫指标以及肝组织结构的影响。试验以初始体重(7.62±0.29) g罗非鱼为研究对象,设置低氧(2.0±0.1 mg/L,A组)和高氧(5.0±0.1 mg/L,B组)养殖环境,并分别饲喂五种脂肪水平(1~5组：1.57 %、4.41 %、7.61 %、10.51 %、13.01 %)的饲料,每组3个重复,养殖60 d。结果显示：随着脂肪水平升高,A组与B组的增重率(WGR)、特定生长率(SGR)和饲料效率(FE)呈先上升后下降趋势,分别在A2组、B3组达到最大值；同一脂肪水平下,B组WGR和SGR显著高于A组(P < 0.05)。肝组织中过氧化氢酶(CAT)、总抗氧化能力(T-AOC)、谷草转氨酶(AST)、热休克蛋白-90(HSP-90)活性和丙二醛(MDA)、己糖激酶(HK)、丙酮酸激酶(PK)、甘油三酯(TG)、肝脂酶(HL)含量均显著受溶氧含量和脂肪水平交互作用的影响(P < 0.05),而两种因素对腺苷三磷酸酶(ATPase)活性不存在交互作用(P ＞ 0.05)；A组免疫指标免疫球蛋白M(IgM)、干扰素-γ(IFN-γ)、肿瘤坏死因子α(TNF-α)、白细胞介素(IL-1β)含量均显著低于B组(P < 0.05),且不受脂肪水平的影响。随着脂肪水平升高,B组肝脏组织脂滴空泡逐渐增多,A2组肝细胞形态结构正常,A3组、A4组和B5组均有大量的脂滴空泡、细胞核溶解和偏移的现象。综上,在本实验范围内,投喂脂肪水平为4.41%左右的饲料有利于缓解罗非鱼由低氧环境造成的氧化应激,而高氧环境中投喂脂肪水平为7.61%左右的饲料有利于促进罗非鱼的生长。

英文摘要:

      Oreochromis niloticus, known as Nile tilapia, has the advantages of boasts rapid growth, versatile feeding habits, absence of intermuscular thorns, and robust stress resistance. Moreover, it is abundant in essential amino acids and unsaturated fatty acids, rendering it highly nutritious. Since 1976, the Food and Agriculture Organization of the United Nations (FAO) has recognized tilapia as a fish suitable for cultivation worldwide. Currently, the farming model for Nile tilapia is gradually shifting from traditional flowing water systems towards high-density factory farming in China. However, oxygen deficiency is a common factor leading to fish mortality in high-density intensive farming settings. Therefore, close attention needs to be paid to the dissolved oxygen (DO) status in the aquaculture environment. DO is essential for maintaining normal metabolic activities in aquatic organisms and has a significant impact on their growth, immunity, and energy metabolism. Studies have found that fish can cope with low oxygen environments through a series of physiological mechanisms. Under hypoxic conditions, fish utilize stored energy reserves (carbohydrate and lipid) to maintain life activities. Due to the low utilization rate of carbohydrates in fish, utilizing lipids to provide energy is the optimal choice for them to adapt to low oxygen environments. Due to the low utilization rate of carbohydrates in fish, utilizing lipids to provide energy is the optimal choice for them to adapt to low oxygen environments. Tilapia subjected to prolonged hypoxia will utilize more lipids in response to hypoxic stress, suggesting that supplementing diet with appropriate lipid levels can enhance fish survival. However, the precise underlying mechanisms remains unclear. This study aims to investigate the interactive effects of DO contents and fat levels on the growth performance, hepatic antioxidant capacity, immune parameters, and liver tissue structure in Nile tilapia. The experiment was conducted using tilapia with an initial weight of (7.62±0.29) g as the subjects. Two DO contents: low DO (2.0±0.1 mg/L, Group A) and high DO (5.0±0.1 mg/L, Group B) and five fat levels: (Groups 1-5: 1.57 %, 4.41 %, 7.61 %, 10.51 %, 13.01 %) were installed, including three replicates per group. The culture period lasted for 60 days. Results showed that as fat levels increased, the weight gain rate (WGR), specific growth rate (SGR), and feed efficiency (FE) of Groups A and B increased firstly and then decreased, reaching maximum values in Groups A2 and B3, respectively. At the same fat level, WGR and SGR were significantly higher in Group B than in Group A (P < 0.05). Hepatic enzyme activities and content of various parameters, including catalase (CAT), total antioxidant capacity (T-AOC), aspartate transaminase (AST), cytochrome c oxidase (CCO), caspase-9, heat shock protein-90 (HSP-90), malondialdehyde (MDA), hexokinase (HK), pyruvate kinase (PK), triglycerides (TG), and hepatic lipase (HL), were significantly affected by the interaction between oxygen levels and fat levels (P < 0.05), while there was no interaction effects on adenosine triphosphatase (ATPase) activity between the two factors. With the increase of lipid level, the activities of CAT and T-AOC in group B and T-AOC in group A were firstly increased and then decreased, and the T-AOC activity in group A was lower than that in group B, and the B3CAT activity was significantly higher than that in other groups (P < 0.05). MDA content in group B increased gradually with the increase of fat level, MDA content in group A decreased first and then increased, and MDA content in group A was higher than that in group B. Under the same lipid level, the activities of CCO and ATPase in group B were significantly lower than those in hypoxia group A (P < 0.05), AST, T-AOC activities and MDA contents in group A were higher than those in group B, while caspase9 activities and HK, PK and HSP90 contents in group B were significantly lower (P < 0.05). Immune indicators including immunoglobulin M (IgM), interferon-gamma (IFN-γ), tumor necrosis factor-alpha (TNF-α), and interleukin-1 beta (IL-1β) were significantly lower in Group A compared to Group B (P < 0.05), and were not affected by fat level. DO content and dietary fat level had significant effects on complement C3 (C3) in liver of Tilapia (P < 0.05). In group A, C3, content first decreased and then increased with the increase of fat level, and was significantly lower in groups A3 and A4 than in other groups (P < 0.05). With increasing fat levels, the number of hepatic lipid vacuoles gradually increased in Group B, while the cell morphology in Group A2 was normal. Groups A3, A4, and B5 showed large amount of lipid vacuoles, nuclear dissolution, and displacement. In summary, both low oxygen and excessive dietary lipid level lead to more severe liver oxidative damage, fat accumulation, lipid metabolism dysfunction, and reduced immune capacity. Within the scope of this experiment, feeding a diet with fat content of approximately 4.41% during low oxygen conditions promotes the growth of Nile tilapia and alleviates hypoxic stress, while feeding a diet with fat content of around 7.61% in high oxygen environments benefits the growth of Nile tilapia.