Abstract
To study the effects of acute ammonia stress on the poisoning reaction of the hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu), 300 healthy grouper juveniles with an initial body weight of 51.4 ± 2.57 g were selected for an acute ammonia stress experiment using a half-lethal concentration of ammonia for 24, 48, 72, and 96 h with triplicate. The results show that (1) The half-lethal concentrations of ammonia for a hybrid grouper were 39.5 mg/L for 24 h, 27.3 mg/L for 48 h, 26.5 mg/L for 72 h, and 25.0 mg/L for 96 h, and the safe concentration was 2.50 mg/L. (2) The biochemical indices of the serum and livers of the groupers fluctuated under acute ammonia stress (P < 0.05), and the contents of serum cortisol and lactate reached the maximum value in 72 h (P < 0.05). (3) 24 h ammonia stress increased the activities of alkaline phosphatase, acid phosphatase, catalase, glutathione peroxidase, superoxide dismutase, lysozyme, and the content of immunoglobulin M in the liver (P < 0.05). Meanwhile, all ammonia-stressed fish groups had an increased amount of malondialdehyde in the liver (P < 0.05). (4) The ammonia poisoning caused significantly up-regulation of antioxidant genes, inflammatory cytokines, and apoptosis genes (P < 0.05), and the expression of inflammatory cytokines and apoptosis genes were the highest in 24 h ammonia stress group. (5) The ammonia content in the water changed the abundance and evenness of intestinal microbes in grouper, mainly in that ammonia stress significantly increased the relative abundance of fusobacteria, but significantly decreased the relative abundance of gemmatimonadetes (P < 0.05). It was speculated that apoptosis induced by ammonia poisoning in grouper may be related to oxidative stress and the activation of inflammatory factors, and excessive inflammatory stress may be one of the causes of ammonia poisoning in the hybrid grouper.
Highlights
The hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) is a new cross-species of grouper that is bred from a giant grouper male parent (Epinephelus lanceolatu) and a brown-marbled grouper female parent (Epinephelus fuscoguttatus), belongs to the Perciformes and grouper
We found that under acute ammonia stress, hybrid groupers appeared to have local hyperemia, and some stress behaviors appeared in the early stage of poisoning, including manic restlessness, frequent collision or rollover, shortness of breath, and increased frequency of gill flap agitation
The results of this study showed that the acute toxicity of ammonia to the groupers was linear with ammonia concentration and stress duration
Summary
The hybrid grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatu) is a new cross-species of grouper that is bred from a giant grouper male parent (Epinephelus lanceolatu) and a brown-marbled grouper female parent (Epinephelus fuscoguttatus), belongs to the Perciformes and grouper. In an intensive aquatic culture system, ammonia is the most common toxic substance and is considered a common stress factor in the culture environment and an important indicator of water quality. When the concentration of ammonia in the water exceeds a certain range, it will cause ammonia poisoning, which may lead to slow growth, tissue erosion, oxidative stress in the body, decreased immunity, and even the death of aquatic animals (Cheng et al, 2015). These physiological changes will differ for different research objects because of their differences in ammonia tolerance (Person-Le Ruyet et al, 1995). It is important to find ways to reduce the damaging effects of ammonia by elucidating the mechanism of ammonia poisoning in aquatic animals
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