Abstract
In pond cultures of juvenile Eriocheir sinensis, limb autotomy stress seriously affects and restricts the quality and economic benefits of aquaculture. This study was designed to evaluate the effects of dietary supplementation of L-tryptophan on E. sinensis under the cheliped autotomy stress. In the present study, 252 crabs were divided into four groups: dietary L-trp supplementation with 0.28, 0.40, 0.53, and 0.70%, and their hematological immunity, antioxidant capacity, anti-stress, and antibacterial ability were evaluated after 14 days of using biochemical analysis, flow cytometry, and molecular biology techniques. First, we counted the mortality after 14 days of feeding and found that compared with other treatments, dietary supplementation of 0.53 and 0.70% L-trp significantly lowered the mortality of E. sinensis. Moreover, the total hemocyte count (THC), hemocyanin, and glutathione (GSH) content, and glutathione peroxidase (GSH-Px) activity significantly increased at 7 and 14 d with dietary supplementation of 0.53 and 0.70% L-trp, in contrast with the significant decrease in malondialdehyde (MDA) content at 14 d in the same dietary groups (P<0.05). Next, the bacterial challenge test after 14 days of feeding showed that the THC levels, phagocytic rate, and acid phosphatase (ACP) and alkaline phosphatase (ALP) activity were significantly higher with dietary supplementation of 0.53 and 0.70% L-trp after 12 and 24 h of Aeromonas hydrophila injection, along with a significant improvement in the antioxidant capacity (P<0.05). Further, we measured the expression of antibacterial-related protein genes (EslecB and HSP 90) and found that they were significant up-regulated in the hepatopancreas, hemocytes, intestine, and gill in the groups with dietary supplementation of 0.53% and 0.70% L-trp after 12 h or 24 h of A. hydrophila injection (P<0.05). Taken together, the observations in this study indicate that dietary supplementation of L-trp can enhance the antioxidant capacity and improve the hematological immune status and antibacterial ability of E. sinensis under the cheliped autotomy stress, thereby increasing the survival rate of E. sinensis under cheliped autotomy stress.
Highlights
The Chinese mitten crab, Eriocheir sinensis, occupies an important position in China’s aquaculture industry, owing to its rich nutritional value and wide market demand
total hemocyte count (THC) Levels and Hemocyanin Content There was no significant difference in the THC levels and hemocyanin content among the four dietary groups at 1 d after the start of the experiment (Figure 3)
The results showed that dietary supplementation of L-trp significantly enhanced the serum antioxidant capacity of E. sinensis that had been injected with A. hydrophila
Summary
The Chinese mitten crab, Eriocheir sinensis, occupies an important position in China’s aquaculture industry, owing to its rich nutritional value and wide market demand. In pond cultures of E. sinensis, various factors, such as fighting, defense, and foraging, can cause a high rate of limb autotomy, [1,2,3,4]. Limb autotomy has many adverse effects on the crabs, including long-term loss of function and energy [5], as well as, decreased feeding efficiency and survival rate [6, 7]. Limb autotomy reduces the ability of immune defense to resist pathogens [8]. Zhao et al reported that coin-sized crabs have up to 30% limb autotomy rate in earthen pond culture conditions of E. sinensis [9]. The problem of limb autotomy stress has seriously affected and restricted the quality and aquaculture economic benefits of E. sinensis, resulting in widespread concern [8, 10, 11]
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