Transcriptome-Based Analysis of the Mechanism of Action of Metabolic Disorders Induced by Waterborne Copper Stress in Coilia nasus.

To reveal the effects of waterborne copper stress on gene expression changes, molecular pathways, and physiological functions in Coilia nasus, juvenile fish were equally divided into two experimental groups, and the copper levels were 1.61 ± 0.03 mg/L (copper-exposed group) and 0 mg/L (control group), respectively. After 4 h, gill tissue samples were collected for transcript sequencing analysis, and two libraries were constructed from the copper treatment group (Cu) and the control group (C) and sequenced using Illumina sequencing technology. The results showed that approximately 40.2-46.0 M clean reads were obtained from each library, and the percentage of uniquely mapped transcripts ranged from 80.57 to 84.93%. A total of 3915 differentially expressed genes (DEGs) were identified under waterborne copper stress, among which 1300 genes were up-regulated, and 2615 genes were down-regulated. Twelve DEGs were randomly selected for quantitative RT-PCR (qRT-PCR) analysis, and the results confirmed that the transcriptome analysis was reliable. Furthermore, the DEGs were subjected to Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and the results showed that most of the DEGs were involved in metabolic pathways, including steroid biosynthesis, glutathione metabolism, and peroxisome proliferator-activated receptor (PPAR) signaling pathways. Furthermore, due to the waterborne copper levels, gsk-3ß was significantly up-regulated, while other metabolism-related genes (tor, pi3k, lpl, aqp7, fabp3) were significantly down-regulated. In addition, the copper-exposed group significantly reduced the expression of some immunity genes (ifn-γ, stat1, cxcl10, and tgf-ß), and enhanced the expression of il-1ß and tnf-α. In summary, these results indicated that copper causes metabolic disorders and insufficient energy supply in the body, and induces oxidative stress, which results in reduced immune functions.

DL-Methionyl-DL-Methionine/DL-Methionine Supplementation Alleviated the Adverse Effects of Dietary Low Fishmeal Levels on Growth and Intestinal Health of Micropterus salmoides.

DL-methionyl-DL-methionine (AQUAVI® Met-Met) (Met-Met) (0.10%, 0.20%, 0.30%, and 0.40%) or DL-methionine (DL-Met) (0.10%, 0.20%, 0.30%, and 0.40%) were added to a low-fishmeal diet in an attempt to reduce fishmeal in the diet of Micropterus salmoides (M. salmoides). The fish were randomly allocated into ten experimental groups (n = 100), each with 4 replicates of 25 fish (16.39 ± 0.01 g) each. Compared to 25% FM, 0.40% of DL-Met and 0.10% of Met-Met promoted growth, and 0.10% of Met-Met decreased FCR. Compared to 25% FM, the supplementation of Met-Met or DL-Met improved the intestinal antioxidant capacity by upregulating the NF-E2-related factor 2-mediated antioxidant factors and enzyme activities and nuclear factor kappa-B-mediated anti-inflammatory factors while downregulating the pro-inflammatory factors, thereby exerting anti-inflammatory effects. Moreover, 0.10% of the Met-Met diet affected the Firmicutes-to-Bacteroidota ratio, increased the levels of Proteobacteria, changed the composition of intestinal flora (Roseburia, Lachnospiraceae_NK4A136_group, and unclassified_Oscillospiraceae), and enhanced intestinal dominant bacteria (Caldicoprobacter, Pseudogracilibacillus, and Parasutterella), leading to improved gut health. In summary, the supplementation of DL-Met or Met-Met alleviated the adverse effect of fishmeal reduction (from 40 to 25%) on the growth performance and intestinal health of M. salmoides.

A delayed and unsynchronized ovary development as revealed by transcriptome of brain and pituitary of Coilia nasus.

Coilia nasus is an anadromous fish that has been successfully domesticated in the last decade due to its high economic value. The fish exhibits a delayed ovary development during the reproductive season, despite breeding and selection for five to six offspring. The molecular mechanism of the delayed ovary development is still unknown, so the obstacles have not been removed in the large-scale breeding program. This study aims to investigate the key genes regulating ovarian development by comparing the transcriptomes of ovarian-stage IV and stage II brain/pituitary of Coilia nasus. Ovarian stages were validated by histological sections. A total of 75,097,641 and 66,735,592 high-quality reads were obtained from brain and pituitary transcriptomes, respectively, and alternatively spliced transcripts associated with gonadal development were detected. Compared to ovarian Ⅱ- brain, 515 differentially expressed genes (DEGs) were upregulated and 535 DEGs were downregulated in ovarian Ⅳ- brain, whereas 470 DEGs were upregulated and 483 DEGs were downregulated in ovarian Ⅳ- pituitary compared to ovarian Ⅱ- pituitary. DEGs involved in hormone synthesis and secretion and in the GnRH signaling pathway were screened. Weighted gene co-expression network analysis identified gene co-expression modules that were positively correlated with ovarian phenotypic traits. The hub genes Smad4 and TRPC4 in the modules were co-expressed with DEGs including Kiss1 receptor and JUNB, suggesting that ovarian development is controlled by a hypothalamic-pituitary-gonadal axis. Our results have provided new insights that advance our understanding of the molecular mechanism of C. nasus reproductive functions and will be useful for future breeding.

Excessive Replacement of Fish Meal by Soy Protein Concentrate Resulted in Inhibition of Growth, Nutrient Metabolism, Antioxidant Capacity, Immune Capacity, and Intestinal Development in Juvenile Largemouth Bass (Micropterus salmoides).

This study investigated the effects of replacing 0% (SPC0), 25% (SPC25), 50% (SPC50), 75% (SPC75), and 100% (SPC100) of fish meal (FM) with soy protein concentrate (SPC) on the growth, nutritional metabolism, antioxidant capacity, and inflammatory factors in juvenile largemouth bass (Micropterus salmoides) (17.03 ± 0.01 g). After 56 days of culturing, various growth parameters including FW, WGR, and SGR were not significantly different among SPC0, SPC25, and SPC50 groups; however, they were significantly higher than those in SPC75 and SPC100 groups. Conversely, significantly lower FCR were determined for the SPC0, SPC25, and SPC50 groups compared with that for the SPC100 group; specifically, no significant difference among SPC0, SPC25, and SPC50 groups was found. Moreover, compared with SPC75 and SPC100 groups, a significantly higher FI was observed in the SPC0 group, whereas a significantly lower SR was observed in SPC100 compared with that in SPC0 and SPC25 groups. Compared with the SPC0 group, significantly lower mRNA levels of tor, rps6, 4ebp1, pparγ, and fas were found in SPC75 and SPC100. Additionally, the mRNA levels of cpt were significantly higher in SPC0, SPC25, and SPC50 groups than in SPC75 and SPC100 groups. Moreover, the mRNA levels of scd and acc remained unchanged for all the groups. Replacement of FM with SPC did not significantly affect the mRNA levels of gk, pk, and pepck. Compared with the SPC0 group, significantly decreased activities of CAT were observed in the SPC50, SPC75, and SPC100 groups, and significantly decreased activities of GSH-Px were observed in the SPC75 and SPC100 groups. In addition, significantly lower activity of SOD was observed in SPC100 compared with the other groups. Moreover, compared with the other groups, the SPC75 and SPC100 groups had significantly decreased and increased contents of GSH and MDA, respectively, while significantly lower mRNA levels of nrf2, cat, sod, and gsh-px were found in SPC50, SPC75, and SPC100; however, significantly higher mRNA levels of keap1 were observed in SPC75 and SPC100 groups. Additionally, significantly higher mRNA levels of il-8 and nf-κb were found in the SPC50, SPC75, and SPC100 groups compared with the SPC0 group. Conversely, significantly lower mRNA levels of il-10 and significantly higher mRNA levels of tnf-α were found in the SPC75 and SPC100 groups compared with the other groups. Compared with the SPC0 group, mucosal thickness and villus height were significantly decreased in the SPC75 and SPC100 groups. Collectively, SPC replacing 50% FM did not affect its growth of juvenile largemouth bass. However, SPC replacing 50% or more FM might inhibit antioxidant capacity and immune capacity to even threaten the SR, resulting in impaired intestinal development in replacing FM level of 75% or more.

Different Starch Sources Affect the Growth Performance and Hepatic Health Status of Largemouth Bass (Micropterus salmoides) in a High-Temperature Environment.

The experiment was designed to investigate the effects of different starch types on the growth performance and liver health status of largemouth bass in a high-temperature environment (33-35 °C). In this study, we designed five diets using corn starch (CS), tapioca starch (TS), sweet potato starch (SPS), potato starch (PS), and wheat starch (WS) as the starch sources (10%). We selected 225 healthy and uniformly sized largemouth bass (199.6 ± 0.43 g) and conducted the feeding experiment for 45 days. The results showed that the WS group had the highest WGR, SGR, and SR and the lowest FCR. Among the five groups, the WS group had the highest CAT activity, SOD activity, and GSH content, while the SPS group had the highest MDA content. Furthermore, oil red O staining of liver samples showed that the TS group had the largest positive region, indicating high lipid accumulation. Lastly, the gene expression results revealed that compared with the WS group, the CS, TS, and SPS groups showed suppressed expression of nrf2, keap1, cat, sod, gpx, il-8, and il-10. Therefore, our results demonstrated the effect of different starch sources on largemouth bass growth performance and hepatic health in a high-temperature environment.