Abstract
Streptococcus has greatly restricted the development of healthy tilapia aquaculture. As a green and efficient feed addition, Acanthopanax senticosus (APS) has been increasingly used in culture, but it is unclear whether it represents a disease-resistant feed. Genetically improved farmed tilapia (GIFT, Oreochromis niloticus) was fed with a feed supplemented with 0 (control), 0.5, 1, 2, 4, and 8‰ APS for 56 days, after which fish were injected with 5.9 × 106 CFU/ml Streptococcus iniae into the abdominal cavity. At 96 h after infection, the cumulative survival of GIFT in control and 0.5‰ APS treatments was significantly lower than in other treatments; at APS supplementation rates of 1 and 2‰, serum glucose, triglycerides, and cholesterol contents were all significantly lower than in control treatment fish. Hepatic glycogen and triglyceride contents of 1‰ APS treatment fish were significantly higher than those in fish in control treatment. Transcription levels of peroxisome proliferator activated receptor α (PPAR), fatty acid synthase (FAS), and lipoprotein Lipase (LPL) genes were upregulated, and their expression levels in fish in 1, 2, and 4‰ treatments were significantly higher than those in fish in control treatment at 96 h after S. iniae infection. After 96 h of infection, the red blood cells, hemoglobin, hematocrit, and white blood cells of fish in 1‰ APS treatment were significantly lower than those of fish in 4 and 8‰ treatments; hepatic catalase activity was activated at 48 h, superoxide dismutase activity was also significantly upregulated at 96 h, and the malondialdehyde content significantly decreased. It is noted that 0.5–2‰ APS treatments significantly activated the expression of PI3K and AKT in the liver, while inhibiting the expression of Caspase-9. Therefore, feed with 1‰ APS can promote hepatic glycogen and lipid metabolism in GIFT after infection with S. iniae, which is beneficial to alleviating oxidative stress damage and cell apoptosis in liver tissue.
Highlights
MATERIALS AND METHODSThe risk of disease has increased with the rapid development of tilapia aquaculture, with Streptococcus being one of the biggest threats to their healthy farming
Improved farmed tilapia began to die after 24 h of being infected with S. iniae, but there was no significant difference in mortality among treatments (P > 0.05) (Figure 1A)
We reported a reduced mortality of GIFT at 96 h after S. iniae infection when their food was supplemented with Acanthopanax senticosus (APS) above 1, but how this occurs remain unclear
Summary
The risk of disease has increased with the rapid development of tilapia aquaculture, with Streptococcus being one of the biggest threats to their healthy farming. Disease from S. iniae spreads fast and causes considerable losses to aquaculture industries in warm water areas due to increased mortalities; it infects at least 27 marine and freshwater fish species at mortality rates as high as 30–50% (Abdel-Latif et al, 2020). The frequency of streptococcal disease is related to the stress response of fish caused by the mode of aquaculture and physical and chemical attributes of the water quality (Qiang et al, 2016; Abdel-Latif et al, 2020). Improved farmed tilapia is currently one of the mainly cultured freshwater fish species in China because of their fast growth and high yield. To determine if APS improves the response and regulation mechanism of GIFT infected with S. iniae, we compared their serum biochemistry, liver antioxidant, lipid metabolism, and PI3K/AKT pathways after feeding GIFT with different APS levels.
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