Effects of Five Dietary Carbohydrate Sources on Growth, Glucose Metabolism, Antioxidant Capacity and Immunity of Largemouth Bass (Micropterus salmoides)

Abstract

This study investigated the effects of glucose (GLU), tapioca starch (TS), gelatinized tapioca starch (GTS), potato starch (PS) and gelatinized potato starch (GPS) on growth and physiological responses in juvenile largemouth bass Micropterus salmoides. After 8 weeks, fish fed with starch diets had better weight gain and growth rates. Counts of red blood cells and monocytes were increased in the PS and GPS groups, compared to GLU group. Contents of serum triglyceride and total cholesterol were markedly elevated in the TS, PS and GPS groups. There were lower levels of serum glucose, insulin and cholecystokinin, and higher agouti-related peptide contents in the PS group compared to GLU group. PS and GPS could enhance glycolysis and TCA cycle by increasing their enzyme activities and transcriptional levels. Additionally, starch sources markedly heightened mRNA levels of key genes involved in the respiratory electron transport chain. Additionally, elevated mRNA levels of key antioxidant genes were shown in the TS and GTS groups. Moreover, TS and PS could promote immunity by upregulating transcriptional levels of the complement system, lysozyme and hepcidin. Taken together, starch exhibited better growth via increasing glycolysis and TCA cycle compared with GLU, and PS could improve antioxidant and immune capacities in largemouth bass.

Keywords: Micropterus salmoides; antioxidant and immune capability; carbohydrate sources; glucose metabolism; growth and hematological parameters.

Figure 1

Effect of dietary carbohydrate sources on mRNA expression levels of genes involved in the glycolysis and citric acid cycle in largemouth bass (n = 3). Bars with different superscripts are significantly different (p < 0.05). HK, hexokinase-1; PFK, phosphofructokinase; PK, pyruvate kinase; MPC2, mitochondrial pyruvate carrier 2; PDHx, pyruvate dehydrogenase complex component X; CS, citrate synthase; IDH, isocitrate dehydrogenase; MDH, malate dehydrogenase.

Figure 2

Effect of dietary carbohydrate sources on mRNA expression levels of genes involved in the glycogen synthesis in largemouth bass (n = 3). Bars with different superscripts are significantly different (p < 0.05). GYG1, glycogenin-1; GYG2, glycogenin-2; UGPα, UTP–glucose-1-phosphate uridylyltransferase; GCS, glycogen synthase; GBE, glycogen branching enzyme.

Figure 3

Effect of dietary carbohydrate sources on mRNA expression levels of mitochondrial respiratory electron transport chain genes in largemouth bass (n = 3). Bars with different superscripts are significantly different (p < 0.05). NDUfa1, NADH:ubiquinone oxidoreductase subunit A1; ND1, NADH dehydrogenase subunit 1; ND2, NADH dehydrogenase subunit 2; SDHb, succinate dehydrogenase complex iron sulfur subunit B; SDHc, succinate dehydrogenase complex iron sulfur subunit C; COX1, cytochrome c oxidase I; COX3, cytochrome c oxidase III; ATP6, ATP synthase 6.

Figure 4

Effect of dietary carbohydrate sources on mRNA expression levels of antioxidant-relative genes in largemouth bass (n = 3). Bars with different superscripts are significantly different (p < 0.05). Cu/Zn-SOD, Cu/Zn-Superoxide dismutase; Mn-SOD, Mn-Superoxide dismutase; CAT, catalase; GSS, glutathione synthase; GR, glutathione reductase; GPX1b, glutathione peroxidase 1b; GPX7, glutathione peroxidase 7; Nrf2, nuclear factor E2-related factor 2; keap1b, Kelch-like ECH associated protein 1b.

Figure 5

Effect of dietary carbohydrate sources on mRNA expression levels of immune genes in largemouth bass (n = 3). Bars with different superscripts are significantly different (p < 0.05). C3, complement component 3; C4, complement component 4; C8a, complement component 8a; C8b, complement component 8b; C8g, complement component 8g; C9, complement component 9; LZM, lysozyme; Hepc, hepcidin; β-actin, actin beta.