Effects of dietary carbohydrate to lipid ratios on growth, biochemical indicators, lipid metabolism, and appetite in Chinese perch (Siniperca chuatsi)

Impacts of live and artificial feed on histology, biochemical indicators, gene expression, and bacterial resistance in mandarin fish (Siniperca chuatsi)

The mandarin fish (Siniperca chuatsi) is a significant freshwater carnivorous species in Chinese aquaculture industry, and its farming scale is continuously expanding. The use of feed in aquaculture has become an increasingly common practice. However, the impacts of substituting artificial feed for live bait on fish's biochemical and immune responses are poorly understood. In this study, two hundred forty mandarin fish (weight: 5.60 ± 0.41 g) were divided into two groups and fed live bait or artificial feed (LB and AF groups) over a 63-day aquaculture experiment. We compared the differences between the two groups in terms of histology, biochemical indicators, gene expression, and bacterial resistance. The results showed that artificial feed promoted enhanced growth, evidenced by higher weight (p < 0.05). The AF group exhibited higher liver and intestinal somatic indices (p < 0.05), and histological examination revealed denser cytoplasmic content in liver cells, less fragmentation of renal tubular epithelial cells, and less detachment of intestinal epithelial cells in the AF group. Regarding biochemical indicators and gene expression, the AF group showed better performance in glucose regulation and lipid metabolism. The AF group maintained glucose balance (p < 0.05) and effectively regulated cholesterol transport (p < 0.05), promoting lipolysis (p < 0.05) while inhibiting lipogenesis (p < 0.05). In contrast, live bait consumption resulted in reduced lipolysis (p < 0.05), increased lipogenesis (p < 0.05), impaired endoplasmic reticulum function (p < 0.05), heightened inflammation (p < 0.05), and diminished antioxidant capacity (p < 0.05). Additionally, the LB group exhibited lower survival rates and lysozyme levels during bacterial challenges. Overall, artificial feed was more beneficial for the growth, regulate physiology and enhance disease resistance of S. chuatsi, highlighting its potential to improve fish health and increase aquaculture yield.

Astaxanthin attenuates glucose-induced liver injury in largemouth bass: role of p38MAPK and PI3K/Akt signaling pathways

BACKGROUND

Astaxanthin (ASX) has been documented to exert beneficial influence on various processes in fish. Largemouth bass (Micropterus salmoides) serves as a common model for studying glucose-induced liver disease, making it imperative to investigate the regulatory mechanisms underlying its liver health.

METHODS

Largemouth bass were fed with a control diet (CON), a high carbohydrate diet (HC), or a HC diet supplemented astaxanthin (HCA) for 8-weeks, followed by the glucose tolerance test (GTT). Primary hepatocytes were treated with low glucose and high glucose combined with different concentrations of astaxanthin for 48 h. The histopathology, enzymology, transcriptomics, molecular biology and cell biology were combined to investigate the mechanism of liver injury.

RESULTS

This study provides evidence for the protective effects of ASX against growth performance reduction and hepatic liver injure in largemouth bass fed HC diet. In GTT, HCA diet exhibited an improvement in glucose tolerance following glucose loading. Although HCA diet did not restore the expression of insulin resistance-related genes in livers at different time during the GTT, the addition of ASX in the long-term HC diet did improve the insulin resistance pathway by regulating the PTP1B/PI3K/Akt signaling pathway. Hepatic transcriptome analyses showed that ASX plays an essential role in the modulation of glucose homeostasis in response to treated with HC diet. In in vitro study, ASX treatment resulted in an exaltation in cell viability and a reduction in the rate of cell apoptosis and reactive oxygen species (ROS). Additionally, astaxanthin was observed to improve apoptosis induced by high-glucose via p38MAPK/bcl-2/caspase-3 signaling pathway.

CONCLUSIONS

Astaxanthin exhibited a protective effect against apoptosis by regulating p38MAPK/bcl-2/caspase-3 pathway, and ameliorated insulin resistance by activating the PTP1B/PI3K/Akt pathway. This study elucidated the mechanism of astaxanthin in the liver injury of largemouth bass from a new perspective and provided a new target for the treatment of insulin resistance.

Molecular Cloning of the scd1 Gene and Its Expression in Response to Feeding Artificial Diets to Mandarin Fish (Siniperca chuatsi)

Background/Objectives: Stearoyl-coenzyme A desaturase 1 (SCD1) plays a crucial role in fatty acid metabolism. However, its roles in the feeding habit transformation of mandarin fish (Siniperca chuatsi) remain largely unknown. Methods: Juvenile mandarin fish (10.37 ± 0.54)g were trained to feed on an artificial diet and then divided into artificial diet feeders and nonfeeders according to their feed preference. Afterwards, the scd1 gene of mandarin fish (Sc-scd1) was identified and characterized, and its transcription difference was determined between S. chuatsi fed live artificial diets and those fed prey fish. Results: Our results show that Sc-scd1 coding sequence is 1002 bp long, encoding 333 amino acids. The assumed Sc-SCD1 protein lacks a signal peptide, and it contains 1 N-linked glycosylation site, 24 phosphorylation sites, 4 transmembrane structures, and 3 conserved histidine elements. We found that Sc-SCD1 exhibits a high similarity with its counterparts in other fish by multiple alignments and phylogenetic analysis. The expression level of Sc-scd1 was detected with different expression levels in all tested tissues between male and female individuals fed either live prey fish or artificial diets. Conclusions: In particular, the Sc-scd1 expression level was the highest in the liver of both male and female mandarin fish fed artificial diets, indicating that scd1 genes may be associated with feed adaption of mandarin fish. Taken together, our findings offer novel perspectives on the potential roles of scd1 in specific domestication, and they provide valuable genetic information on feeding habits for the domestication of mandarin fish.

Dietary zinc levels affect growth, appetite, and lipid metabolism of Chinese perch (Siniperca chuatsi)

An 84-day feeding experiment was conducted to investigate the effects of dietary Zn (zinc) on growth performance, food intake, and lipid metabolism of Chinese perch (Siniperca chuatsi). Five isonitrogenous and isolipidic diets with differential Zn contents (67, 100, 149, 230, and 410 mg/kg) were fed to 270 fish (35.47 ± 0.49 g). Results showed that fish growth and food intake increased markedly with the dietary 149 mg/kg Zn levels. Meanwhile, the food intake of 149 mg/kg group was significantly higher than that of other treatment groups after feeding for 8 weeks (P < 0.05). The qRT-PCR results showed that the expression of center appetite regulation factors in the hypothalamus was significantly regulated, and 149 mg/kg significantly increased mRNA expression of npy (neuropeptide Y) and decreased pomc (anorexigenic proopiomelanocortin) and cart (cocaine- and amphetamine-regulated transcript) gene expression. Meanwhile, the expressions of the main genes (such as leptin A and ghrelin) involved in peripheral appetite regulation factors were significantly up-regulated firstly and then reduced with the dietary Zn level increased, whereas the expression of cck (cholecystokinin) was significantly up-regulated. Serum AST (aspartate transaminase) and ALT (alanine transaminase) activities in fish fed the diets containing 230 and 410 mg/kg were significantly higher than that in other groups (P < 0.05). The lipid content of liver in 67 and 100 mg/kg groups was significantly higher than other groups (P < 0.05). Furthermore, dietary Zn significantly elevated the serum TG (triglyceride) and TCHO (total cholesterol) content levels (P < 0.05). Fish fed a high Zn diet (149, 230, and 410 mg/kg) dramatically down-regulated expression of srebp1 (sterol regulatory element binding proteins1c) and fas (fatty acid synthetase), but up-regulated expression of pparα (peroxisome proliferators-activated receptor-α) and cpt1 (carnitine palmitoyl transferase I) in the liver. The optimal dietary Zn inclusion level ranged from 146.69 to 152.86 mg/kg diet, based on two-slope broken-line regression analysis of WGR (weight gain rate) and FCR (feed conversion rate) for Chinese perch.

Study on the Adaptive Regulation of Light on the Stress Response of Mandarin Fish (Siniperca chuatsi) with Re-Feeding after Starvation

Light influences the stress response to environmental stimuli and feeding behaviors of Siniperca chuatsi and, thus, is an important regulator of normal growth and development. In this study, we first explored the important role of light on the digestive and stress capacity of S. chuatsi by studying the changes in physiological and biochemical indicators of S. chuatsi, taking the re-feeding after starvation as the constant environmental stimulus and the light intensity as the adjustable environmental stimulus. The activity of protease and lipase was generally higher in the stomach tissues than in the intestinal tissues, especially lipase, which was higher in stomach tissues under all light conditions, and the protease and lipase activity peaked in the stomach tissues of S. chuatsi at a light intensity of 18.44 ± 3.00 lx and in intestinal tissues at 11.15 ± 2.01 lx, respectively, indicating that greater light intensity increased the digestive capacity of stomach tissues, whereas lower light intensity facilitated the digestive capacity of intestinal tissues. The tissues of the gill, stomach, and intestine had relatively high activity of stress-related enzymes, whereas the tissues of the brain, kidney, liver, and plasma samples had relatively low activity of enzymes. Collectively, the results show that light intensity at 11.15 ± 2.01 lx promoted digestive capacity in the intestine and enhanced the anti-stress ability of S. chuatsi in response to stress induced by re-feeding after starvation. These findings should prove useful for artificial breeding of S. chuatsi.

Effects of flow velocity on the growth performance, antioxidant activity, immunity and intestinal health of Chinese Perch (Siniperca chuatsi) in recirculating aquaculture systems

The cultivation of Chinese Perch (Siniperca chuatsi) in recirculating aquaculture systems (RASs) has become a common trend. To explore the effect of flow velocity on the growth performance, antioxidant activity, immunity and intestinal health of Chinese Perch in RAS, 240 Chinese Perch with an initial weight of 70.66 ± 0.34 g were selected and randomly divided into 4 groups: control group [CK, 0 body length per second (bl/s)], low flow velocity (LF, 0.4 bl/s), middle flow velocity (MF, 0.8 bl/s) and high flow velocity (HF, 1.2 bl/s) for a 56-days experiment. The results showed that the flow velocity significantly increased the weight gain rate and feed intake in Chinese Perch. At 1.2 bl/s, the flow velocity increased the intestinal trypsin content and intestinal villus length. Furthermore, the relative expression of appetite-related genes showed a tendency to increase, and the relative expression of appetite-inhibiting genes had a significant decrease in HF. Regarding immune-related indicators, the activities of alanine aminotransferase (ALT) and aspartate transaminase (AST) were significantly higher in MF and HF. However, the activities of lysozyme (LZM) significantly decreased. Moreover, the activities of total superoxide dismutase (T-SOD) and catalase (CAT) were significantly higher in the CK group than in the other groups. Excessive flow velocity also caused the mRNA level of most immune-relevant genes to markedly decrease. With regard to intestinal health, the intestinal content sequencing results showed that MF could increase the intestinal diversity index of Chinese Perch. In addition, with increasing flow velocity, the relative abundance of Proteobacteria gradually increased, while the proportion of Firmicutes decreased. In conclusion, although the high flow velocity could promote growth, feeding, and digestion, inhibit fat deposition and increase the intestinal microbial abundance, the flow velocity caused stress, which leads to a decline in immunity and increases the death rate and the risk of intestinal disease in Chinese Perch. These findings provide theoretical support for the development of RASs for Chinese Perch.

The toxicity of nano polyethylene terephthalate to mice: Intestinal obstruction, growth retardant, gut microbiota dysbiosis and lipid metabolism disorders

Polyethylene terephthalate (PET) are widely used in our daily life while they may be broken to smaller fractions as nano-sized PET (nPET) in the environment. The toxicity of nPET is still less studied. This work first evaluated the LD50 of different size of nPET (200 nm, S-nPET; 700 nm, B-nPET) in mice, then studied the health effects of single exposure to S/B-nPET at 200 mg/kg bw for 30 days. It was found that the LD50 was 266 mg/kg bw for S-nPET and 523 mg/kg bw for B-nPET, respectively, showing a size-dependent effect. S-nPET caused weight loss, cyst, intestinal obstruction, organ damage and mortality (40%), and perturbed gut microbiome and metabolome especially lipid metabolism, such as upregulated cholesterol, glycocholic, propionic acid, niacinamide, ectoine and xanthine, and downregulated arachidonic acid, anserine, histamine, while B-nPET did not. Serological analysis found S-nPET brought more lipid metabolic immune and neurological damage than B-nPET, confirming the size-dependent effect. To the best of our knowledge, this is the first report on the systematic toxicity of nPET to mice. Further studies are warranted for life-long effects of nPET. The protocol applied in this work may also be used for the study of the health effects of other plastics.

Brewer's spent yeast replacement in carp diet leads to muscle biomass production, recycling, waste management and resource conservation

Brewer's spent yeast (BSY) is among the most voluminous by-products generated in brewery industry that adds to the waste; however, smart utilization of BSY could lead to edible biomass production besides waste management. To utilize it for biomass production, it is being used in fish feeds; however, its effect on the fish physiology has been scantily studied. The present study investigated the proteomic changes in muscle tissues of carp Labeo rohita fed with BSY-based diet, to understand its impact on muscle physiology and biomass. Six feeds were prepared with different grades of BSY (0, 20, 30, 40, 50, 100% replacement of fishmeal with BSY) and fishes were fed for 90 days. Highest weight gain%, feed conversion efficiency, specific growth rate% were observed in 30% BSY-replaced group and this group was considered for the proteomic study. Comparative shotgun proteomic analysis was carried out by LC-MS/MS and data generated have been deposited in ProteomeXchange Consortium with dataset identifier PXD020093. A total of 62 proteins showed differential abundance; 29 increased and 33 decreased in the 30% BSY-replaced group. Pathway analysis using IPA and Panther tools revealed that the proteins tyrosine protein kinase, PDGFα, PKRCB and Collagen promote muscle growth by inducing the PI3K-AKT pathway. Conversely, the proteins Serine/threonine-protein phosphatase, Phosphatidylinositol 3,4,5-trisphosphate5-phosphatase 2A and Ras-specific guanine- nucleotide-releasing factor inhibit muscle growth indicating that 30% BSY-replaced feed promote muscle growth in a highly controlled manner. Findings suggest that BSY could be recycled for carp feed production in large scale thereby leading to resource conservation, reducing environmental effects.