A 56 day feeding trial was conducted to examine the effects of different levels of dietary histamine on growth performance, immune response, and intestinal health of grouper (Epinephelus coioides). Seven isonitrogenous (46%), isolipidic (10%) diets were prepared with histamine supplement levels of 0 (T0), 0.05% (T1), 0.1% (T2), 0.15% (T3), 0.2% (T4), 0.25% (T5), and 0.3% (T6), respectively. The results showed that histamine supplementation had no significant effects on weight gain rate (WGR), specific growth rate (SGR), feed conversion rate (FCR), hepatosomatic index (HSI), and survival rate (SR) at the initial feeding period (day 0–28), but WGR and SGR had negative linear responses to the dietary histamine level at the whole feeding period (day 0–56), and a significant decrease was observed in groups T5 and T6 compared with T0 (P < 0.05). Supplementation of histamine decreased antioxidant capacity, immune response, the contents of serum interleukin-1 beta (IL-1β), intestinal-type fatty acid-binding protein (FABP2) and intestinal trefoil factor (ITF), and caused serious damage of intestine with significantly decreased VH and MFH of grouper, especially in fish fed with diets supplemented with high doses of histamine (0.25 and 0.3%). The intestinal microbial communities in treatments were different clearly with the control (T0), in terms of beta (β)-diversity boxplots and UPGMA phylogenetic tree based on unweighted unifrac distance. At the phylum level, the relative abundance of Fusobacteria was lower in group T0, while the abundance of Firmicutes was significantly lower in groups T5 and T6 (P < 0.05). At the genus level, the relative abundance of uncultured_bacterium_f_Bacteroidales_S24-7_group, uncultured_bacterium_f_Lachnospiraceae, and Ruminiclostridium were significantly higher in the control, while the abundance of Cetobacterium was significantly higher in groups T5 and T6 (P < 0.05). In conclusion, the present study suggested that up to 0.2% of dietary histamine did not result in a remarkable reduction in growth, immune response, and intestinal health; however, 0.25% or more dietary histamine could cause significant negative effects on growth performance, immune response, and intestinal health in E. coioides.

Vibriosis is one of the most common bacterial diseases that cause high rates of mortality and considerable economic losses in aquaculture. Phage therapy has been considered as a promising alternative method to antibiotics in the biocontrol of infectious diseases. Genome sequencing and characterization of the phage candidates are prerequisites before field applications to ensure environmental safety. In this study, a lytic phage, named vB_VhaS-R18L (R18L), was isolated from the coastal seawater of Dongshan Island, China. The phage was characterized in terms of morphology, genetic content, infection kinetics, lytic profile, and virion stability. Transmission electronic microscopy indicated that R18L is siphovirus-like, comprising an icosahedral head (diameter 88.6 ± 2.2 nm) and a long noncontractile tail (225 × 11 nm). Genome analysis indicated R18L to be a double-stranded DNA virus with a genome size of 80,965 bp and a G + C content of 44.96%. No genes that encode known toxins or genes implicated in lysogeny control were found in R18L. A one-step growth experiment showed that R18L had a latent period of approximately 40 min and a burst size of 54 phage particles per infected cell. R18L showed lytic activity against a wide range of at least five Vibrio species (V. alginolyticus, V. cholerae, V. harveyi, V. parahemolyticus, and V. proteolyticus). R18L was relatively stable at pH 6–11 and at temperatures ranging from 4°C to 50°C. The broad lytic activity across Vibrio species and the stability in the environment make R18L a potential candidate for phage therapy in controlling vibriosis in aquaculture systems.

The purpose of this study was to investigate how pre-hypoxia exposure affected the mitochondrial structure and bioenergetic function of large yellow croaker in responding to Cu stress. Fish were acclimated to normoxia and 3.0 mg DO L^-1 for 48 h, then subjected to 0 and 120 μg Cu L^-1 for another 48 h. Hypoxic acclimation did not affect mitochondrial ultrastructure and reactive oxygen species (ROS), but reduced oxidative phosphorylation (OXPHOS) efficiency. Cu exposure impaired mitochondrial ultrastructure, increased ROS generation and inhibited OXPHOS efficiency. Compared with Cu exposure alone, hypoxic acclimation plus Cu exposure reduced ROS production and improved OXPHOS efficiency by enhancing mitochondrial respiratory control ratio, mitochondrial membrane potential, and activities and gene expressions of electron transport chain enzymes. In conclusion, hypoxic acclimation improved the mitochondrial energy metabolism of large yellow croaker under Cu stress, facilitating our understanding of the molecular mechanisms regarding adaptive responses of hypoxia-acclimated fish under Cu stress.