Dietary Methionine Level Impacts the Growth, Nutrient Metabolism, Antioxidant Capacity and Immunity of the Chinese Mitten Crab (Eriocheir sinensis) under Chronic Heat Stress

Abstract

This study examined whether diets with high dietary methionine levels could alleviate chronic heat stress in Chinese mitten crab Eriocheir sinensis. Crabs were fed three dietary methionine levels of 0.49%, 1.29% and 2.09% for six weeks. The analyzed methionine concentration of diets was 0.48%, 1.05% and 1.72%, respectively. Crabs were fed three different supplemental concentrations of dietary methionine at 24 °C and 30 °C, respectively. The trial was divided into six groups with five replicates in each group, and 40 juvenile crabs (initial average weight 0.71 ± 0.01 g) in each replicate. During the trial, crabs were fed twice daily (the diet of 4% of the body weight was delivered daily). The effects of dietary methionine level on nutrient metabolism, antioxidant capacity, apoptosis factors and immunity were evaluated at a normal water temperature of 24 °C and high temperature of 30 °C. Feed conversion ratio decreased under chronic heat stress. Chronic heat stress increased weight gain, specific growth rate, molting frequency, and protein efficiency ratio. The survival of crabs decreased under chronic heat stress, whereas a high level of dietary methionine significantly improved survival. Chronic heat stress induced lipid accumulation and protein content reduction. The high-methionine diet decreased lipid in the body and hepatopancreas, but increased protein in the body, muscle and hepatopancreas under chronic heat stress. Simultaneously, the high dietary methionine levels mitigated oxidative stress by reducing lipid peroxidation, restoring the antioxidant enzyme system, decreasing apoptosis and activating immune function under chronic heat stress. This study suggests that supplementing 1.72% dietary methionine could alleviate the adverse effects of a high water temperature in E. sinensis farming.

Keywords: Eriocheir sinensis; antioxidant capacity; chronic heat stress; dietary methionine level; immunity; nutrient metabolism; oxidative stress.

Figure 1

The total lipid (A) and triglyceride contents (B) in the hepatopancreas of juvenile E. sinensis fed the experimental diets at normal (24 °C)/high water temperature (30 °C). * means that there is a significant difference between different temperatures at the same dietary methionine level (p < 0.05). The A and B indicate significant differences among crabs fed diets with different dietary methionine levels at high water temperature (p < 0.05).

Figure 2

The lipid metabolism of juvenile E. sinensis fed the experimental diets at normal water temperature (24 °C)/high water temperature (30 °C). (A) srebp-1: sterol-regulatory element binding protein 1; (B) fas: fatty acid synthase; (C) elovl6: elongase of very-long-chain fatty acids 6; (D) cpt-1α: carnitine palmitoyl transterase 1α; (E) caat: carnitine acetyltransferase; (F) mttp: microsomal triglyceride transfer protein. * means that there is a significant difference between different temperatures at the same dietary methionine level (p < 0.05). The a, b and c indicate significant differences among crabs fed diets with different dietary methionine levels at normal temperature (p < 0.05). The A and B indicate significant differences among crabs fed diets with different dietary methionine levels at high water temperature (p < 0.05).

Figure 3

The crude protein content in hepatopancreas (A) and the crude protein in muscle (B) of juvenile E. sinensis fed the experimental diets at normal (24 °C)/high water temperature (30 °C). * means that there is a significant difference between different temperatures at the same dietary methionine level (p < 0.05). The a, b and c indicate significant differences among crabs fed diets with different dietary methionine levels at normal temperature (p < 0.05). The A and B indicate significant differences among crabs fed diets with different dietary methionine levels at high water temperature (p < 0.05).

Figure 4

The antioxidative capacity of juvenile E. sinensis fed the experimental diets at normal (24 °C)/high water temperature (30 °C). (A) MDA: malondialdehyde; (B) SOD: superoxide dismutase; (C) CAT: catalase; (D) GSH-Px: glutathione peroxidase; (E) GSH content. * means that there is a significant difference between different temperatures at the same dietary methionine level (p < 0.05). The a, b and c indicate significant differences among crabs fed diets with different dietary methionine levels at normal temperature (p < 0.05). The A and B indicate significant differences among crabs fed diets with different dietary methionine levels at high water temperature (p < 0.05).

Figure 5

The apoptosis of juvenile E. sinensis fed the experimental diets at normal water temperature (24 °C)/high water temperature (30 °C). (A) Caspase 3: cysteine–aspartic acid protease 3; (B) caspase 8: cysteine–aspartic acid protease 8; (C) bax: B-cell lymphoma-2-associated X; (D) bcl-2: B-cell lymphoma-2. * means that there is a significant difference between different temperatures at the same dietary methionine level (p < 0.05). The a and b indicate significant differences among crabs fed diets with different dietary methionine levels at normal temperature (p < 0.05). The A, B and C indicate significant differences among crabs fed diets with different dietary methionine levels at high water temperature (p < 0.05).

Figure 6

The toll-like receptor-related pathway of juvenile E. sinensis fed the experimental diets at normal water temperature (24 °C)/high water temperature (30 °C). (A) Hsp90: heat shock protein 90; (B) tlr2: toll-like receptor 2; (C) myd88: myeloid differentiation factor 88; (D) tube; (E) dorsal. * means that there is a significant difference between different temperatures at the same dietary methionine level (p < 0.05). The a and b indicate significant differences among crabs fed diets with different dietary methionine levels at normal temperature (p < 0.05). The A and B indicate significant differences among crabs fed diets with different dietary methionine levels at high water temperature (p < 0.05).