The newly bred strawberry cultivar ‘Jingxiang’ (JX) is favored by consumers for its intense aroma and pronounced peach-like attributes. However, its molecular basis and ripening-associated change remains insufficiently elucidated. SPME and SAFE combined with GC-O-QTOF were used to characterize odor-active compounds (OACs) across five ripening stages. At full-red stage, 64 OACs were identified. Esters dominated both concentration and flavor dilution (FD) factors, with ethyl benzoate and γ-decalactone reaching FD values of 128. Moreover, furaneol exhibited a pronounced individual impact (FD = 512), serving as a key contributor to sweetness and strawberry-like aroma. Dynamic analysis revealed a marked restructuring of the aroma profile during ripening, shifting from aldehyde- and alcohol-dominated green notes at early stages to ester- and terpene-driven sweet fruity aromas, while furanones persisted and further enhanced sweetness. These findings provide quantitative chemical markers for flavor-oriented quality assessment, optimal harvest determination, and targeted breeding of aromatic strawberry cultivars.

Temperature is one of the most prevalent environmental factors that affects the growth and development of organisms. The survival of aquatic animals is closely related to the changes in temperature, low temperature could cause physiological damage even death. In this study, we revealed the regulatory mechanisms of lowtemperature stimulation from the transcriptomics in the hepatopancreas of the red swamp crayfish, Procambarus clarkii. Transcriptome sequencing revealed that lipid metabolism pathways were significantly enriched at low temperature. Crayfish improved their cold tolerance by increasing expression levels of thermogenic gene prdm16 and uncoupling protein genes ucp4 and ucp5. Furthermore, lipid and triglyceride content increased significantly in cold-sensitive crayfish, which in turn increased the expression levels of proinflammatory factors (cox2 and tgf beta r) and the amount of hepatopancreas bacteria. In addition, low-temperature stimulation could cause more severe damage to cold-sensitive crayfish spermatophores, accompanied by downregulated of spermatozoa viability-related genes such as alp and ldh. Estradiol 17 beta-dehydrogenase 8-like (17 beta de8) may contain a critical SNP site at exon 544, the bases of this site were "G" in cold-tolerant crayfish and "A" in cold-sensitive crayfish. Above all, our results reveal that lipid metabolism is the main factor affecting cold tolerance in crayfish and reveal the key loci for cold tolerance, providing a reference for cold tolerance breeding.

Accompanied by the increased intake of carbohydrate-rich foods, the utilization of carbohydrate is enhanced across generations of humans, but little is known about its epigenetic mechanism. In this study, zebrafish fed with carbohydrate-rich diets for two months (carbohydrate-programming group, PG), showed the better utilization of carbohydrates than those fed with carbohydrate-normal diets (normal group, NG) in the first and the second high-carbohydrate diet challenge, including the preference for ingesting glucose, and the enhanced carbohydrate absorption and metabolism. The maternal zebrafish were mated with wild type males, and the utilization of carbohydrates was also improved in the offspring from the PG. Through RNA-seq and ATAC-seq of offspring, beside of the higher expression of glut2 gene related to glucose absorption and phip gene related to carbohydrate metabolism, the mRNA level of H3K9me2-specific histone methyltransferase gene ehmt2 was down-regulated, while the demethylase gene kdm4a was significantly up-regulated, and then the protein levels of H3K9me2 was decreased in the PG. Furthermore, the regulatory relationship of H3K9me2 with glut2 and phip was demonstrated by the treatment with the ehmt2 inhibitor BRD4770 in vitro, administration of the kdm4a inhibitor PKF-118-310 in vivo, combining with the methods of dual-luciferase, ChIP and siRNA. Therefore, the improved carbohydrate utilization induced by maternal programming could be inherited through epigenetics, provide new insights into human dietary nutrition plans and therapeutic targets for diabetes.

The current researches on food addiction focus on the diagnostic criteria, neurobiological theory, relationship of obesity and treatment. However, little is reported on the relationship between food addiction and feeding habit, especially in fish. In the present study, in vitro, the signaling pathway of food addiction of lysine and glucose in the brain cells of Chinese perch ( Siniperca chuatsi) was determined. In vivo, the behavior experiment of food addiction was conducted on zebrafish ( Danio rerio). In vitro, we found that lysine had a positive regulatory effect on food addiction signaling pathway and orexigenic factor Agrp expression, and the effect was suppressed with the inhibitors treatment of the signaling c-Fos/Mor/Drd1, whereas glucose exhibited a contrary trend. In vivo, the zebrafish were fed with the diets containing the normal lysine/carbohydrate level (Control Group1/2, CG1/2) or high lysine/carbohydrate level (Food Addiction Group1/2, FAG1/2) for 31 days during the food addiction formation. At Day 7, 12, 18, 23, 28 and 31, the food intake experiment showed that the FAG1 fish ingested the gelatin bait containing the high lysine diets more than the CG1 fish, and the increase trend was eliminated by the inhibitor of Mor (FAG1 + inhi). In the food selection experiment, the FAG1 fish preferred to ingest the gelatin bait containing the high lysine diets more than that containing the control diets, and the increase trend was eliminated in the FAG1 + inhi fish. Zebrafish existed the lysine addiction, which could modulate the food selection through the signaling pathway of food addiction and Agrp. Our data illustrated for the first time that food addiction to nutrients such as lysine exists in fish and that it is regulated by the food addiction signaling pathway c-Fos/Mor/Drd1/Agrp.

Herbivore-induced plant volatiles (HIPVs) are crucial chemical cues guiding insect herbivores and their natural enemies to the potential hosts. However, the effects and underlying mechanisms of HIPVs on insect development and reproduction remain underexplored. This study investigated the cotton bollworm Helicoverpa armigera-induced cotton volatiles as well as their impacts on larval performance, adult fecundity and transcriptome of H. armigera. Upon cotton bollworm feeding, the volatile compositions of cotton leaves, calyxes, and bolls were altered, with (Z)-3-hexenyl acetate (HAC) being the most significantly induced volatile. HAC exposure had negative effects on H. armigera, including reduced food intake, slower larval growth, prolonged larval lifespan, and a significant decrease in adult fecundity. RNA-Seq and qRT-PCR analysis revealed that HAC exposure altered the expression of genes related to cuticles, muscles, and juvenile hormone metabolism in larvae. In adults, the transcriptome changes were less pronounced and mainly associated with carbohydrate metabolism. Our results suggest that cotton bollworm feeding induces HAC production, which negatively impacts bollworm development and reproduction by modulating gene expression. These findings provide new insights into the role of HIPVs in insect herbivore physiology and their potential for biological control.

Metabotropic glutamate receptor 4 (mGluR4) is widely regarded as an umami receptor activated by L-glutamate to exert essential functions. Numerous studies have shown that umami receptors participate in food intake regulation. However, little is known about mGluR4’s role in mediating food ingestion and its possible molecular mechanism. Mandarin fish, a typical carnivorous fish, is sensitive to umami substances and is a promising vertebrate model organism for studying the umami receptor. In this study, we identified the mGluR4 gene and conducted evolutionary analyses from diverse fish species with different feeding habits. mGluR4 of mandarin fish was cloned and functionally expressed to investigate the effects of L-glutamate on mGluR4. We further explored whether the signal pathway mGluR4-Ca2+-ERK1/2 participates in the process in mandarin fish brain cells. The results suggest that L-glutamate could regulate Neuropeptide Y (Npy) via the mGluR4-Ca2+-ERK1/2 signaling pathway in mandarin fish. Our findings unveil the role of mGluR4 in feeding decisions and its possible molecular mechanisms in carnivorous fishes.

The melanocortin 4 receptor (MC4R) is a G protein-coupled transporter that mediates the regulation of thyroid hormones and leptin on energy balance and food intake. However, the mechanisms of transcriptional regulation of Mc4r by thyroid hormone and leptin in fish have been rarely reported. The messenger RNA expression of Mc4r gene was significantly higher in brain than those in other tissues of mandarin fish. We analyzed the structure and function of a 2029 bp sequence of Mc4r promoter. Meanwhile, overexpression of NKX2.1 and incubation with leptin significantly increased Mc4r promoter activity, but triiodothyronine showed the opposite effect. In addition, mutations in the NKX2.1 binding site abolished not only the activation of Mc4r promoter activity by leptin but also the inhibitory effect of thyroid hormones on Mc4r promoter activity. In summary, these results suggested that thyroid hormones and leptin might regulate the transcriptional expression of Mc4r through NKX2.1.

Soybean meal, excessively used in place of fish meal (FM) in aquaculture, has a detrimental impact on fish. In this study, the nanopeptide C-I20, which was created by conjugating antimicrobial peptide gcIFN-20H and CMCS, were evaluated the feeding effect in mandarin fish (Siniperca chuatsi). Compared with the control group, 150 mg/ kg C-I20-fed fish showed the second highest growth performance with no significant changes in body composition. C-I20-fed fish showed more goblet cells and thicker mucin after feeding. The 150 mg/kg C-I20 diet boosted the antioxidant capacity, immunity, and digestive enzymes. After Aeromonas hydrophila and infection spleen and kidney necrosis virus infection, the survival rates in the 150 mg/kg C-I20 group were highest. Meanwhile, many tissues in the 150 mg/kg C-I20 group had significantly lower pathogen loads than the other groups. Treatment with 150 mg/kg C-I20 was effective in increasing antioxidant capacity and immunity. The minimum tissue lesions were observed in the 150 mg/kg C-I20 group. The goblet cell number and mucin thickness were significantly increased by C-I20 treatment after infection. The study results herein showed that a reasonable dietary concentration of C-I20 feed promoted growth performance and disease resistances in fish, suggesting a prospective nano antimicrobial peptide for the aquaculture.

Proopiomelanocortin (POMC) is a hormone precursor, and has been reported to participate in domestication. However, its effects on feeding habit domestication in fish are poorly understood. Mandarin fish (Siniperca chuatsi) feeds solely on live prey fish since first-feeding. In the present study, the high expression of pomc in mandarin fish, both the pomc siRNA and MC4R inhibitor treatments increased the success rate of domestication from live prey fish to dead prey fish and food intake of dead prey fish, suggesting the role of pomc on the special feeding habit of live prey fish in mandarin fish. In addition, one c-fos binding site was identified in the region that from -1053 bp to -931 bp upstream of the transcription start site of pomc, and this region exhibited positive promoter activity. The mandarin fish brain cells treated with c-fos siRNA displayed suppressed pomc mRNA expression, indicating that c-fos positively regulated pomc expression. Furthermore, the mRNA expression of c-fos was higher in the mandarin fish which were more difficult to domesticate. The results of ChIP assay and inhibitor treatment confirmed that the activation of c-fos gene by histone H3K4me3 was catalyzed by Setd1b in mandarin fish. Three open peaks were found at the upstream regulatory region of setd1b by ATAC-seq, and the mRNA expression of setd1b was higher in the mandarin fish which were more difficult to domesticate. These results indicated that Setd1b could methylate histone H3K4 to activate the c-fos transcription, maintaining the high expression of pomc, which might contribute to the special feeding habit of mandarin fish.

[This corrects the article DOI: 10.3389/fendo.2023.1160378.].

Mandarin fish ( Siniperca chuatsi ) is one of the most economically important fish in China. However, it has the peculiar feeding habit that it feeds solely on live prey fish since first-feeding, while refuses dead prey fish or artificial diets. After the specific training procedure, partial individuals could accept dead prey fish and artificial diets. The genetic basis of individual difference in artificial diet feeding habit is still unknown. In the present study, the resequencing was performed between 10 individuals which could be domesticated to accept artificial diets and 10 individuals which could not. Through the selective sweep analysis based on heterozygosity ( Hp ) and population differentiation coefficient ( Fst ), 57 candidate windows were identified as the putative selected regions for feeding habit domestication of mandarin fish, involved in 149 genes. These genes were related to memory, vision and olfaction function, which could be potential targets of molecular marker assistant breeding of artificial diet feeding trait. Beside of the DNA sequence, we also explored the potential role of DNA methylation in feeding habit domestication in mandarin fish. Whole-genome bisulfite sequencing was performed between the individuals which could be domesticated to accept artificial diets and those could not. 5,976 differentially methylated regions were identified, referring to 3,522 genes, such as the genes involved in cAMP signaling pathway. The DNA methylation changes of these genes might contribute to the adaption of artificial diets in mandarin fish. In conclusion, the putative selected regions and the differentially methylated regions were identified in the whole genome, providing new insights into the feeding habit domestication from live prey fish to artificial diets in mandarin fish. And the involved genes were identified as the candidate genes for molecular breeding of artificial diet utilization in mandarin fish.

The mandarin fish (Siniperca chuatsi) is an important economic fish species in China. Many carnivorous fish larvae feed on zooplankton or microdiets. However, the mandarin fish larvae feed on live prey fish exclusively, while refusing zooplankton or microdiets. A stable supply of palatable live prey fish results in high costs. Moreover, the application of live prey fish might bring the risk of pathogens. However, little is known about the genes underlying the food preference of mandarin fish larvae. Partial offspring of the domesticated strain could feed brine shrimp from three days post-hatching (dph), the open mouth day. In the present study, the mandarin fish larvae were randomly divided into three groups, then treated differently at 3 dph: (1) unfed; (2) fed with live prey fish; (3) fed with brine shrimp (Artemia). Differentially expressed genes were identified by RNA-seq. The differential expression of the transcription factors involved in retinal photoreceptor development and differentiation might contribute to the intake of brine shrimp in mandarin fish larvae. Meanwhile, the digestive enzyme genes involved in protein, fat, and carbohydrate digestion have been expressed in mandarin fish larvae at 3 dph, contributing to the digestion of ingested food. Our study provides an overview of genes and biological processes involved in the peculiar food preference at the first-feeding stage in mandarin fish larvae and has critical importance to the future application of non-fish live feeds in the culture of mandarin fish larvae.

Antibacterial peptide has been widely developed in cultivation industry as feed additives. However, its functions in reducing the detrimental impacts of soybean meal (SM) remain unknown. In this study, we prepared nano antibacterial peptide CMCS-gcIFN-20H (C-I20) with excellent sustained-release and anti-enzymolysis, and fed mandarin fish (Siniperca chuatsi) with a SM diet supplemented with different levels of C-I20 (320, 160, 80, 40, 0 mg/Kg) for 10 weeks. 160 mg/Kg C-I20 treatment significantly improved the final body weight, weight gain rate and crude protein content of mandarin fish and reduced feed conversion ratio. 160 mg/Kg C-I20-fed fish maintained appropriate goblet cells number and mucin thickness, as well as improved villus length, intestinal cross-sectional area. Based on these advantageous physiological changes, 160 mg/Kg C-I20 treatment effectively reduced multi-type tissue (liver, trunk kidney, head kidney and spleen) injury. The addition of C-I20 did not change the muscle composition and muscle amino acids composition. Interestingly, dietary 160 mg/Kg C-I20 supplementation prevented the reduction in myofiber diameter and change in muscle texture, and effectively increased polyunsaturated fatty acids (especially DHA + EPA) in muscle. In conclusion, dietary C-I20 in a reasonable concentration supplementation effectively alleviates the negative effects of SM by improving the intestinal mucosal barrier. The application of nanopeptide C-I20 is a prospectively novel strategy for promoting aquaculture development.

Carnivorous fish have poor tolerance to carbohydrate in feed and low utilization rate of carbohydrate. Therefore, the balance of carbohydrate and lipids in the nutrient metabolism of carnivorous fish, the effective conversion and utilization of carbohydrate and lipids, and the feedback regulation of feeding are the key links for the efficient utilization of carnivorous fish feed. Carbohydrate response element binding protein (ChREBP) is a new transcription factor found in recent years in the glucose signaling pathway, and can also participate in feeding regulation. We performed in-vivo and in-vitro experiments to reveal the role of ChREBP in the glucose metabolism and feeding in mandarin fish. The mRNA expression of ChREBP and appetite regulatory factors were measured after intraperitoneal injection of glucose in mandarin fish Siniperca chuatsi and cotransfection with glucose and glucose+siRNA in the hypothalamic cells in mandarin fish. The results reveal that at hour 2 and 4 post intraperitoneal injection with 1 mg/g BW glucose, the blood glucose level of the mandarin fish increased significantly, but food intake decreased significantly, and it also displayed a significantly increased ChREBP mRNA expression levels in liver. At hour 4 post injection, hypothalamic ChREBP mRNA level was significantly increased, whereas the mRNA expression levels of appetite genes neuropeptide Y (npy) and agouti-related peptide (AgRP) were decreased significantly. When the glucose concentration was 40 mmol/L, the expression level of ChREBP mRNA in mandarin fish hypothalamic cells was significantly up-regulated, but the expression level of appetite gene npy mRNA was down-regulated. When siRNA and glucose were co-transfected into mandarin fish brain cells, the expression level of chrebp mRNA was significantly decreased, and the appetite gene npy mRNA was significantly increased. The results indicated that glucose regulated food intake through the modulation of appetite gene npy by ChREBP.

Low occurrence of swimbladder inflation often leads to vertebral skeletal malformations and poor swimming ability, which exert numerous effects on growth, feeding, buoyancy regulation and survival rate of fish larvae. In the present study, 713 mandarin fish (Siniperca chuatsi) larvae samples ranging from 5 to 11 days post hatch (DPH) were collected to detect the rate of swimbladder inflation and calculate the body density of each sample. Swimbladder inflated fish larvae were increased with the development of DPH except 7 DPH, with 86.21% in 11 DPH whereas 27.59% in 5 DPH. Our results indicate that 5–11 DPH is the main stage for swimbladder inflation in mandarin fish larvae, following the onset of exogenous feeding. The body density of swimbladder inflated (SBI) fish larvae (0.983 ± 0.016 g/cm3) was lower than the swimbladder non-inflated (SBN) ones (1.023 ± 0.018 g/cm3), while SBI fish larvae were significant heavier (p < 0.05) than SBN group. These findings suggest that swimbladder non-inflation could significantly influenced the neutrally buoyancy maintained and live bait predation in mandarin fish. The research will contribute to understanding the influence of initial swimbladder inflation on larviculture of mandarin fish.

Proenkephalin (PENK), as the precursor of endogenous opioid enkephalin (ENK), is widely present in the nervous system and plays an important role in animal food addiction and rewarding behavior. In our study, we intend to study the functional characterization and molecular marker development of the penk gene related to food habit domestication of mandarin fish. We found that the penk gene of mandarin fish had three types of endogenous opioid peptide sequences. Compared with other tissues, penk mRNA was highly expressed in the whole brain. Intracerebroventricular (ICV) injection of lysine or methionine significantly increased the expression of penk mRNA. The expression of penk mRNA in the brain of mandarin fish that could be easily domesticated from eating live prey fish to artificial diets was significantly higher than those that could not. After feeding with high-carbohydrate artificial diets, the expression of penk mRNA showed no significant difference between mandarin fish with hypophagia and those that still ate normally. A total of four single nucleotide polymorphisms (SNP) loci related to easy domestication toward eating artificial diets were screened from the mandarin fish population. Additionally, the TT genotype at one of the loci was significantly correlated with the food habit domestication of mandarin fish.

Regulation of food intake is associated with nutrient-sensing systems and the expression of appetite neuropeptides. Nutrient-sensing systems generate the capacity to sense nutrient availability to maintain energy and metabolism homeostasis. Appetite neuropeptides are prominent factors that are essential for regulating the appetite to adapt energy status. However, the link between the expression of appetite neuropeptides and nutrient-sensing systems remains debatable in carnivorous fish. Here, with intracerebroventricular (ICV) administration of six essential amino acids (lysine, methionine, tryptophan, arginine, phenylalanine, or threonine) performed in mandarin fish (Siniperca chuatsi), we found that lysine and methionine are the feeding-stimulating amino acids other than the reported valine, and found a key appetite neuropeptide, neuropeptide Y (NPY), mainly contributes to the regulatory role of the essential amino acids on food intake. With the brain cells of mandarin fish cultured in essential amino acid deleted medium (lysine, methionine, histidine, valine, or leucine), we showed that only lysine deprivation activated the general control nonderepressible 2 (GCN2) signaling pathway, elevated α subunit of eukaryotic translation initiation factor 2 (eIF2α) phosphorylation, increased activating transcription factor 4 (ATF4) protein expression, and finally induced transcription of npy. Furthermore, pharmacological inhibition of GCN2 and eIF2α phosphorylation signaling by GCN2iB or ISRIB, effectively blocked the transcriptional induction of npy in lysine deprivation. Overall, these findings could provide a better understanding of the GCN2 signaling pathway involved in food intake control by amino acids.

The purpose of this study is to compare the effects of three live feeds for the larvae of the domesticated strain of mandarin fish (Siniperca chuatsi). Larvae of this strain of mandarin fish with salinity activation ingested Artemia nauplii was firstly observed. The larvae at 3 days post hatch (dph) were reared from first feeding to 9 dph and fed on starving (no food supplied), zebrafish (Danio rerio) (newly hatched larvae), Artemia nauplii and Daphnia magna, respectively. The results showed that the highest survival was found in the newly hatched larvae group (41.7 ± 1.5 %), and the lowest growth was found in the Daphnia group, respectively. A high food intake was found in the Artemia nauplii group, and the npy expression between the Artemia nauplii and newly hatched larvae groups had no significant difference (p＞0.05), whereas they were significantly lower than that of the starving group (p＜0.05). At the first feeding day, the activities of amylase, lipase and trypsin and the target of rapamycin (tor) expression in the Artemia nauplii and newly hatched larvae groups were significantly higher than those of the starving group. These results suggested that larvae of this strain of mandarin fish could feed on the newly hatched larvae and Artemia nauplii, and both of them could be digested, but the digestion might be insufficient in the Artemia nauplii group. Together, this study indicates that larvae of this strain of mandarin fish can ingest and digest Artemia nauplii during first-feeding.

This study is aimed to explore the differences of gut microbiota and lipid metabolism in Chinese perch (Siniperca chuatsi) with different growth rates. After 180 days post-fertilization, among the population of Chinese perch (1,275 fish in total), 36 fish with different growth rates were selected from the low growth rate group (L group, initial weight 87 +/- 2 g), the medium growth rate group (M group, initial weight 223 +/- 4 g) and the high growth rate group (H group, initial weight 468 +/- 13 g), respectively, with a total of 108 fish. The microbial species abundance and evenness in both M and H groups were obviously higher than those in the L group. The activities of lipase and trypsin in the gut showed a similar changing trend to the intestinal microbial diversity in L, M and H groups. The M and H groups showed a similar microbial composition, but they had different main functional bacteria. There were more microbial species in the H group than in the M group. Butyricicoccus might be used as an indicator to distinguish the growth rate of the M and H group. The intraperitoneal fat ratio and levels of triglyceride and total cholesterol in the plasma increased gradually with the increase in the growth rate. A large amount of fat accumulation was observed in the liver and gut of the H group, and the H group showed significantly higher levels of low-density lipoprotein and high-density lipoprotein in the plasma compared with the L and M groups. It was also found that the fat of the L and M groups mainly accumulated in the liver and gut, respectively, and the level of low-density lipoprotein in the plasma of the M group than that in the L group. The mRNA level of fas and srebp1 decreased gradually with the increase in the growth rate. The M and H group had high mRNA levels of ppar alpha and cpt1 than the L group. The mRNA levels of lpl and hl were higher in the H group than those in the L and M groups.