Physiological trade-off of marine fish under Zn deficient and excess conditions.

Fish can regulate their Zn body bioaccumulation, but the mechanisms and physiological responses at the organ level are still largely unknown. In the present study, we exposed the marine seabreams under different Zn levels (deficient, optimum and excess levels) over a period of 4 weeks and examined how fish maintained its regulation of bioaccumulation with associated physiological effects at the fish intestinal organ. Our results indicated that fish intestinal organs constantly controlled the Zip family to "rob" more Zn under Zn-deficiency (with a dietary level of 7.9 mg/kg), whereas restricted the Zn efflux to preserve the intestinal function. Under Zn-excess conditions (193.3 mg/kg), the fish intestine maintained a limited Zn homeostasis (37.8-44.6 µg/mg) by initially inhibiting the influx through the Zip family receptor, but later accelerating both influx and efflux of Zn. Based on the WGCNA method, Zn deficient dietary exposure first resulted in defense response with subsequent switching to antioxidant defense. Instead, excess Zn first triggered the immunological response, but then led to physiological toxicity (abnormal in lipid metabolism). Although Zn had multiple biological functions, it was preferentially involved in lipid metabolism under different dietary Zn doses. This study provided direct evidence for Zn regulation at the organ level and detoxification mechanisms against potential environmental toxicity in fish.

Responses of two marine fish to organically complexed Zn: Insights from microbial community and liver transcriptomics.

The diversity and adjustability of metal-organic complex enhance the function of metals and promote the burgeoning fields of chemical biology. In the present study, we chose two marine fish to explore the effects of a dihydromyricetin (DMY)-Zn(II) complex on the intestinal microbiome composition and liver biological function using high-throughput sequencing technology. Two economic fish species commonly found in Southern China (golden pompano Trachinotus ovatus and pearl gentian grouper ♀Epinephelus fuscoguttatus × â™‚Epinephelus lanceolatus) were exposed to dietary DMY-Zn complex for 4-week. Our study found that DMY-Zn performed a vital function on the improved anti-oxidative ability of both fish species. The Zn complex improved the stability of microbial community structure of the golden pompano by enhancing the α-diversity, but its impacts on the composition and diversity of intestine microorganisms of grouper were insignificant. BugBase results showed that the intestine microbiota following DMY-Zn exposure contained a lower abundance of potentially pathogenic bacteria and higher abundance of aerobic bacteria. Intestine health and utilization of carbohydrates were improved in the golden pompano, and unclassified bacteria were significantly enriched in the grouper. Liver transcriptome indicated that DMY-Zn affected the oxidative phosphorylation process (OXPHOS). Specifically, the OXPHOS process (map00190) was activated by promoting the glucose uptake (map04251, map04010) in golden pompano and lipid metabolism (map00071, map00140, map00062 and map00564) in grouper. Such difference in the responses of intestine microbiome and liver metabolism may be possibly explained by their different Zn basal requirements. Our study demonstrated that different fish species may have different responses to dietary DMY-Zn complex. The results provided a reference for the application of new additives in aquatic animal feed, and new insights into the roles of metal-organic complex in their biological impacts on fish.

Multi-omics reveals the regulatory mechanisms of zinc exposure on the intestine-liver axis of golden pompano Trachinotus ovatus.

Metal zinc (Zn) has been the focus of many environmental toxicological studies, but there are limited studies on its potential dietary molecular toxicity and physiology. The present study was the first to use multi-omics-based approaches to explore the fish intestine-liver axis under dietary Zn exposure. Golden pompano Trachinotus ovatus were exposed to different dietary concentrations (78.4, 134.6, and 161.4 mg/kg as the control, low-dose Zn, and high-dose Zn groups, respectively) of Zn for 4-week. Low-dose Zn exposure significantly promoted the fish growth, whereas the high-dose Zn exposure reduced the fish growth. Co-analysis of 16S diversity, metagenome and transcriptome showed that the low-dose Zn enriched the intestinal microflora and changed the dominant microflora abundances (Proteobacteria, Fusobacteria, Firmicutes and Bacteroidetes), as well as activated the growth hormone metabolism in the liver. Meanwhile, the high-dose of Zn caused the intestinal microbiota dysbiosis, activated the Type VI secretion systems (T6SSs), and further triggered the oxidative stress response, immunity, and antiviral function of the liver. Multi-omics revealed the interference of long-term Zn dietary exposure on the intestine-liver axis. There was an apparent homeostasis of Zn accumulation in the fish tissues, but the window of dietary Zn nutritional requirements versus toxicity appeared to be narrow for the golden pompano. These results provided new insight into the adverse effects and regulatory mechanisms of dietary Zn requirements and toxicity in marine fish.

Over high or low dietary protein levels depressed the growth, TOR signaling, apoptosis, immune and anti-stress of abalone Haliotis discus hannai.

A 120-day feeding trial was conducted to investigate the effects of relative higher and lower dietary protein levels on the growth, immunity and anti-stress of abalone Haliotis discus hannai fed diets with 17.64% (low), 30.49% (normal) and 43.27% (high) of proteins, respectively. The results showed that compared with 30.49% of dietary protein, 17.64% and 43.27% of dietary protein levels significantly decreased the weight gain rate and the activities of α-amylase, trypsin, alanine aminotransferase and aspartate aminotransferase in the hepatopancreas and serum of abalone (P < 0.05). Abalone fed 30.49% of dietary protein had the highest activity of superoxidase, acid phosphatase, alkaline phosphatase, lysozyme and the total anti-oxidative capacity, and the lowest content of malondialdehyde in the serum and hepatopancreas (P < 0.05). The gene expressions of TOR, S6k, Bcl-2, IκB, NfκB, TNF-α and Nrf2 were significantly up-regulated in the group with 30.49% of dietary protein (P < 0.05). Pathological abnormalities in hepatocyte cells of abalone were found in the groups with 17.64% and 43.27% of dietary protein. Meanwhile, accumulative mortalities of abalone after the Vibrio parahaemolyticus challenge test and heat stress test were significantly increased within these two groups (P < 0.05). In conclusion, the excessive (43.27) or deficient (17.64) dietary protein levels depressed the growth and immunity of abalone. Combined with the stress tests results, 17.63% or 43.27% of dietary protein contents are not recommended to the abalone facing the stress of vibriosis or high-water temperature (≥28 °C).

Effects of Yeast Autolysate in the Practical Diet on the Growth Performance, Immune Response, and Disease Resistance of Pacific White Shrimp.

The present study was conducted to investigate the effects of supplementing the practical diet with yeast autolysate (YA) on the growth performance, immunity, and disease resistance of Pacific white shrimp Litopenaeus vannamei. Four isonitrogenous and isolipidic practical diets were formulated. The relatively high-fish-meal control diet contained 25% fish meal without YA supplementation (E1). The other control diet contained 20% fish meal without YA (E2). With the E2 diet as the basis, two additional experimental diets were created by further supplementation with 1% YA (E3) and 2% YA (E4). The shrimp (initial weight: 0.30 ± 0.02 g) were fed with the four experimental diets for 8 weeks and then challenged with Vibrio parahaemolyticus. The results indicated that there were no significant differences in survival rate (SR) or feed intake (FI) among these groups. The weight gain rate (WGR) of group E1 was not significantly different from that of groups E3 and E4. The feed conversion ratio (FCR) in group E4 was lower than that of group E2, and group E4 had the highest protein efficiency ratio (PER). The total hemocyte counts (THC) and lysozyme activities in group E3 and group E4 were significantly higher than those of the other groups. Group E3 had the highest respiratory burst (RB). After V. parahaemolyticus administration, group E3 and group E4 had significantly lower cumulative mortalities than group E1 did. In conclusion, the 20% fish meal diet without YA supplementation (E2) yielded a significantly lower growth rate than the 25% fish meal diet without YA supplementation (E1) did. Furthermore, the Pacific white shrimp that received dietary supplementation with 1% YA demonstrated improved growth rate, immune response, and resistance to the V. parahaemolyticus challenge compared with those that were fed the 20% fish meal diet without YA supplementation (E2).