Phosphorus Nutrition in Songpu Mirror Carp (Cyprinus carpio Songpu) During Chronic Carbonate Alkalinity Stress: Effects on Growth, Intestinal Immunity, Physical Barrier Function, and Intestinal Microflora

Abstract

Carbonate alkalinity is a major environmental stress factor affecting aquatic feed configuration, which easily causes oxidative stress and hypoimmunity for fish. Hence, the purpose of the study is to assess the potential effect of phosphorus on growth, intestinal oxidation resistance, physical barrier function, and microflora for Songpu mirror carp (Cyprinus carpio Songpu) (initial average weight of 2.95 ± 0.21 g) reared at the high-concentration carbonate alkalinity environment. A two-factor, three-level (2 × 3) design was applied, in which diets with three different phosphorus levels (3.6, 7.0, and 10.5 g/kg dry matter) were randomly assigned to 0 and 15 mmol/L carbonate alkalinity groups with three replicate aquariums. After the 8-week trial, we found that weight gain rate (WGR), specific growth rate (SGR), protein efficiency ratio (PER), and lipase and amylase activities in the intestine significantly (p < 0.05) declined with increasing carbonate alkalinity. Carbonate alkalinity of 15 mmol/L significantly reduced glutathione peroxidase (GSHPx) activities in the intestine (p < 0.05). The relative expressions of nuclear factor (erythroid-derived 2)-like 2 (Nrf2), glutathione peroxidase 1a (GPX1a), Clautin3, Clautin11, and tumor necrosis factor β (TNF-β) in the intestine were markedly downregulated by increasing carbonate alkalinity levels (p < 0.05), whilst the relative expressions of interleukin 1β (IL-1β) and tumor necrosis factor α (TNF-α) in the intestine were markedly upregulated (p < 0.05). At the 15 mmol/L carbonate alkalinity treatment, Songpu mirror carp suffer from hypoimmunity status with failed digestion, antioxidant, inflammation, and immune response, thereby inducing impaired growth. Additionally, significant increments in the abundance of Proteobacteria and a significant decrease in the abundance of Fusobacteria and the Firmicutes/Bacteroidetes ratio were caused due to excessively high carbonate alkalinity (15 mmol/L) and excessively low dietary phosphorus supply (3.6 g/kg). Collectively, 7.0 g/kg dietary phosphorus supplementation was effective in promoting intestinal antioxidant enzyme activities and the corresponding gene expression via the Keap1-Nrf2 signaling pathway and in enhancing intestinal immunity by upregulating anti-inflammatory and downregulating pro-inflammatory genes. Appropriate dietary phosphorus supply could promote the formation of beneficial microflora in freshwater, and it has the potential ability to transfer the adverse effect of carbonate alkalinity stress to the structural composition of intestinal microflora. Hence, consideration should be given to suitable phosphorus supply for fish under the chronic carbonate alkalinity stress.

Physiological Response of Spotted Seabass (Lateolabrax maculatus) to Different Dietary Available Phosphorus Levels and Water Temperature: Changes in Growth, Lipid Metabolism, Antioxidant Status and Intestinal Microbiota

“…Similar results were also observed in crucian carp (Carassius auratus) [30], grass carp (Ctenopharyngodon idella) [31], and rainbow trout (Oncorhynchus mykiss) [32]. In addition, a study on Songpu Mirror Carp (Cyprinus carpio Songpu) found that P supplementation in the diet promoted intestinal health and feed utilization [33]. In this study, it was also found that an available P level of 0.71% diet significantly increased the feed utilization of spotted seabass compared to a basal diet with an available P level of 0.35%, which was probably responsible for the improvement in fish growth.…”

H2O2-Induced Oxidative Stress Responses in Eriocheir sinensis: Antioxidant Defense and Immune Gene Expression Dynamics

“…Extensive studies have demonstrated that variations in salinity, alkalinity, dissolved oxygen, temperature, and ammonia nitrogen within the aquatic environment can induce defense responses in organisms, including oxidative stress responses [15][16][17][18]. Under such stress conditions, the continuous production of ROS can disrupt the balance between the oxidative and antioxidant system, inflicting oxidative damage on lipids, proteins, DNA, and carbohydrates.…”

Water physicochemical factors and oxidative stress physiology in fish, a review

“…Carbonate alkalinity, a significant environmental stressor that can swiftly cause oxidative stress and hypo immunity in fish, substantially impacts the structure of aquatic feed. In addition to exerting effects on the growth, immunity, and disease resistance of aquatic organisms, prolonged exposure to carbonate alkalinity stress can also influence the in-vivo nutrition metabolism of fish (Fan et al, 2021(Fan et al, , 2022.…”