Pyloric Caeca Research Articles

Identification of hub genes in digestive system of mandarin fish (Siniperca chuatsi) fed with artificial diet by weighted gene co-expression network analysis

Mandarin fish (Siniperca chuatsi) is a carnivorous freshwater fish and an economically important species. The digestive system (liver, stomach, intestine, pyloric caecum, esophagus, and gallbladder) is an important site for studying fish domestication. In our previous study, we found that mandarin fish undergoes adaptive changes in histological morphology and gene expression levels of the digestive system when subjected to artificial diet domestication. However, we are not clear which hub genes are highly associated with domestication. In this study, we performed WGCNA on the transcriptomes of 17 tissues and 9 developmental stages and combined differentially expressed genes analysis in the digestive system to identify the hub genes that may play important functions in the adaptation of mandarin fish to bait conversion. A total of 31,657 genes in 26 samples were classified into 23 color modules via WGCNA. The modules midnightblue, darkred, lightyellow, and darkgreen highly associated with the liver, stomach, esophagus, and gallbladder were extracted, respectively. Tan module was highly related to both intestine and pyloric caecum. The hub genes in liver were cp, vtgc, c1in, c9, lect2, and klkb1. The hub genes in stomach were ghrl, atp4a, gjb3, muc5ac, duox2, and chia2. The hub genes in esophagus were mybpc1, myl2, and tpm3. The hub genes in gallbladder were dyst, npy2r, slc13a1, and slc39a4. The hub genes in the intestine and pyloric caecum were slc15a1, cdhr5, btn3a1, anpep, slc34a2, cdhr2, and ace2. Through pathway analysis, modules highly related to the digestive system were mainly enriched in digestion and absorption, metabolism, and immune-related pathways. After domestication, the hub genes vtgc and lect2 were significantly upregulated in the liver. Chia2 was significantly downregulated in the stomach. Slc15a1, anpep, and slc34a2 were significantly upregulated in the intestine. This study identified the hub genes that may play an important role in the adaptation of the digestive system to artificial diet, which provided novel evidence and ideas for further research on the domestication of mandarin fish from molecular level.

Changes in the histology and digestive enzyme activity during digestive system development of silver pomfret (Pampus argenteus)

Silver pomfret (Pampus argenteus) is an economically important marine fish species in the Indian and Western Pacific oceans, it has great aquaculture potential. Research on the ontogeny of the digestive system is critical in improving the larval rearing protocols and weaning process. In this study, an approach that integrates histology and biochemistry was used to illustrate the digestive system ontogeny of silver pomfret from hatching to 50 days post-hatching (dph). At 1 dph, the digestive system was differentiated into the esophageal sac, esophagus, anterior and posterior intestine, liver, pancreas, and gall bladder, and except for pepsin, digestive enzymes were detected. At 4 dph (4.0 ± 0.2 mm in total length, TL), the mouth opened to allow for exogenous feeding, which coincided with the development of papillae and mucous cells in the esophageal sac, indicating their preliminary function of grinding food. At 7 dph (4.5 ± 0.2 mm, TL), the larvae entered an exclusively exogenous feeding stage and numerous supranuclear vacuoles appeared in the posterior intestine. From 1 to 10 dph, alkaline phosphatase increased sharply, suggesting the rapid development of enterocytes and intestine. At 10 dph (4.8 ± 0.6 mm, TL), gastric glands appeared in the stomach, and from 14 to 20 dph (5.2 ± 0.3 to 6.1 ± 0.4 mm, TL), they multiplied greatly. At this time, the other digestive organs, including the esophageal sac, pyloric caeca, intestine, and accessory glands were well developed and tended to mature in structure. From 15 to 20 dph, the activity of pepsin, trypsin, lipase, and α-amylase rapidly increased, suggesting that the digestive system might have become functionally integrated. After reaching enzyme activity peaks, alkaline phosphatase, lipase, and α-amylase decreased significantly while pepsin and trypsin initially decreased and then increased to a second peak at 50 dph (25.0 ± 4.6 mm, TL). Except for the esophageal sac, the ontogeny of the digestive system in silver pomfret larvae appears to be generally similar to that of other marine fish species; it might be feasible to begin weaning this species from 15 to 20 dph, which would reduce the amount of live food as required by current protocols. This study provides a preliminary insight into the digestive system ontogeny of silver pomfret and establishes an initial step towards the rearing and weaning process optimization of this novel species.

Individual and combined effects of deoxynivalenol (DON) with other Fusarium mycotoxins on rainbow trout (Oncorhynchus mykiss) growth performance and health

This study assessed whether the toxicological effects of deoxynivalenol (DON) produced by Fusarium graminearum in rainbow trout (Oncorhynchus mykiss) are altered by the co-exposure to a mixture of toxins produced by Fusarium verticillioides (FUmix). This FUmix contained fusaric acid and fumonisin B1, B2 and B3. Four diets were formulated according to a 2 × 2 factorial design: CON-CON; CON-FUmix; DON-CON; and DON-FUmix. Diets with and without DON contained on average 2700 and 0 µg/kg feed, respectively. The sum of the analysed FUmix toxins was 12,700 and 100 µg/kg feed in the diets with and without FUmix, respectively. The experiment consisted of a 6-week restrictive feeding period immediately followed by a 2-week ad libitum feeding period. Growth performance measurements were taken per feeding period. Histopathological measurements in the liver and gastrointestinal tract (pyloric caeca, midgut and hindgut) were assessed at the end of week 1 and week 6 of the restrictive feeding period and at week 8, the last day of the ad libitum feeding period. During both restrictive and ad libitum feeding, the effects of FUmix and DON on growth performance were additive (no interaction effect; p > 0.05). During the restrictive feeding period, exposure to DON (p ≤ 0.001) and FUmix (p ≤ 0.01) inhibited growth and increased feed conversion ratio (FCR). During this period, DON exposure decreased the protein (p ≤ 0.001) and energy retention (p ≤ 0.05) in the trout. During the ad libitum feeding period, FUmix affected HSI (p ≤ 0.01), while DON exposure reduced feed intake (p ≤ 0.001) and growth (p ≤ 0.001) and increased FCR (p ≤ 0.01). In general, for both liver and intestinal tissue measurements, no interaction effects between DON and FUmix were observed. In the liver, histopathological analysis revealed mild alterations, increased necrosis score by DON (p ≤ 0.01), increased glycogen vacuolization by FUmix (p ≤ 0.05) and decreased percentage of pleomorphic nuclei by FUmix (p ≤ 0.01). DON had a minor impact on the intestinal histological measurements. Over time, some of the liver (glycogen vacuolization score, pleomorphic nuclei; p ≤ 0.01) and intestinal measurements (mucosal fold and enterocyte width; p ≤ 0.01) were aggravated in fish fed the FUmix contaminated diets, with the most severe alterations being noted at week 8. Overall, the co-exposure to FUmix and DON gave rise to additive effects but showed no synergistic or antagonistic effects for the combination of DON with other Fusarium mycotoxins.

Telomere dynamics in the Pacific crown-of-thorns seastar (Acanthaster cf. solaris): effect of age, diet, and tissue type

Population irruptions of crown-of-thorns seastar (CoTS, Acanthaster spp.) represent a perennial threat to Indo-Pacific coral reefs. Age determination of CoTS is challenging, thereby hindering understanding and management of this nuisance species. Telomeres, which are protective DNA structure found at the ends of eukaryotic chromosomes that shorten at each cell division, have been used to estimate age in wild animals. To investigate the use of telomeres in CoTS, we optimized a quantitative PCR protocol to measure relative telomere length (rTL) in CoTS for the first time. Comparing rTL among four age groups (4, 7, 16, > 24 months post-settlement), we found that adult CoTS generally exhibit shorter rTL than juveniles, which is the first evidence of age-related telomere attrition in CoTS. However, there was large within-age class variation, and no significant relationships were found between adult CoTS rTL and potential age-indicating external features. Furthermore, we found accelerated telomere attrition under sub-optimal diet, where individuals that were fed crustose coralline algae for 16 months exhibited shorter rTL than their counterparts fed on coral. A positive correlation was found between rTL of tube feet and pyloric caeca, suggesting synchronization of telomere dynamics across somatic tissues in CoTS. Overall, our results suggest that rTL could be used to classify CoTS into broad age groups, though individual variation constrains the ability to resolve specific cohorts. The present study contributes to the understanding of telomere dynamics in marine invertebrates, while laying the groundwork for future research into rTL as biomarker for age and potentially stress for CoTS.

Effects of two delivery matrix components, alginate and polyethylene glycol, on the intestinal tract and inflammatory response of juvenile rainbow trout, Oncorhynchus mykiss, Walbaum

AbstractA critical step in the administration of oral vaccines in aquaculture is the effective protection of the vaccine antigens through the delivery route of water to stomach to the mucosal immune system in the gut. Bioactive substances can be incorporated into protective matrices to ensure safe ingestion and controlled release into the posterior digestive tract. Polyethylene glycol and alginate are promising and frequently applied substances in the oral administration of pharmaceutical substances; however, their direct influence on the intestinal tract or inflammatory response is not well investigated in aquaculture fish. In the current study, these two substances were evaluated separately and in combination. They were included in a commercial diet for juvenile rainbow trout (18.7 ± 0.1 g) and applied over 22 days in controlled feeding to determine possible gut alterations and inflammatory responses. Three different sections of the intestine, the anterior pyloric caeca, the mid‐intestine, and the posterior intestine, were histologically examined, and expression of inflammatory genes was measured in each. The inclusion of polyethylene glycol in the diet led to a significant reduction of villus height in the pyloric caeca and thus a significant reduction in active surface area. In the mid‐intestine, alginate inclusion resulted in a significant reduction of the mucus‐secreting goblet cells and a significant increase in villus width. In the posterior intestine, polyethylene glycol inclusion caused a significant increase in number of large vacuoles present; the addition of alginate buffered this effect. The results of the histological evaluation indicated symptoms that are usually evident in intestinal inflammation and can reduce functions of the respective intestinal segments. No significant increases in pro‐inflammatory gene expression tumor necrosis factor‐α, interleukin (IL)‐8, or IL‐1β were present, indicating no severe inflammatory response. Based on the observed histological impairments, negative consequences such as reduced efficiency of an oral vaccine or productivity of aquaculture rearing due to hindered nutrient digestion can be considered unlikely.

The development of the digestive system and the fate of the yolk syncytial layer in postembryogenesis of Stenodus leucichthys nelma (Teleostei).

Stenodus leucichthys nelma is an economically important species for cold-water aquaculture. Unlike other Coregoninae, S. leucichthys nelma is a piscivore. Here, we describe in detail the development of the digestive system and the yolk syncytial layer from hatching to early juvenile stage using histological and histochemical methods to determine their common and specific characteristics and to test the hypothesis that the digestive system of S. leucichthys nelma rapidly acquires adult features. The digestive tract differentiates at hatching and starts to function before the transition to mixed feeding. The mouth and anus are open, mucous cells and taste buds are present in the buccopharyngeal cavity and esophagus, pharyngeal teeth have erupted, the stomach primordium is seen, the intestinal epithelium with mucous cells is folded and the intestinal valve is observed; the epithelial cells of the postvalvular intestine contain supranuclear vacuoles. The liver blood vessels are filled with blood. The cells of exocrine pancreas are loaded with zymogen granules, and at least two islets of Langerhans are present. However, the larvae remain dependent on maternal yolk and lipids for a long time. The adult features of the digestive system develop gradually, the most significant changes take place approximately from 31 to 42 days posthatching. Then, the gastric glands and pyloric caeca buds appear, the U-shaped stomach with glandular and aglandular regions develops, the swim bladder inflates, the number of islets of Langerhans increases, the pancreas becomes scattered, and the yolk syncytial layer undergoes programmed death during the larval-to-juvenile transition. During postembryonic development, the mucous cells of the digestive system contain neutral mucosubstances.

Evaluation of probiotic potentiality of GM-Lac (Lactobacillus and Bifidobacterium) in juvenile Asian seabass Lates calcarifer

This study was conducted to evaluate the probiotic potentiality of GM-Lac (a mixture that comprises four lactic acid bacteria (LAB) strains– Limosilactobacillus fermentum GMNL-93, Lactiplantibacillus plantarum GMNL-141, Lacticaseibacillus casei GMNL-277, and Bifidobacterium lactis GMNL-550) applied in fish aquaculture. First, the four LAB isolates (GMNL-93, −141, −277, and −550) constituting GM-Lac were tested individually for antimicrobial activity in vitro. Then, GM-Lac was incorporated in fish feed at a dose of 5 × 106 cfu (g feed)−1 and fed to Asian seabass (Lates calcarifer) juveniles for eight weeks to assess the effects on growth performance, gastrointestinal (GI) histology and microflora, muscle amino acid composition, and disease resistance. According to the result of the zone of inhibition test, each GMNL strain presented noticeable antimicrobial activity against bacterial pathogens common in aquaculture. After the 8-week feeding trial, the fish in the GM-Lac group had higher final weight (p < 0.05), percent weight gain, specific growth rate, and feed intake than the fish in the Ctrl group, along with higher microvillus length in GI tract (p < 0.05) and greater total amino acid concentration in muscle. Furthermore, the relative abundance of microbial phyla in the GI tract of the fish fed with GM-Lac changed significantly, accompanied by increasing probiotic bacteria and decreasing pathogenic bacteria in the intestine and pyloric caeca. In the challenge test, the fish receiving GM-Lac all survived without any clinical symptoms when challenged with Streptococcus iniae. This study concludes that GM-Lac (the combination of L. fermentum GMNL-93, L. plantarum GMNL-141, L. casei GMNL-277, and B. lactis GMNL-550) is recommended as a probiotic supplement with high potential in aquaculture practice, which has antimicrobial activities against aquatic pathogens and benefits in enhancing growth performance, intestinal health, muscle amino acid composition, and disease resistance in juvenile Asian seabass.

Identification and characterization of Myxobilatus channi n. sp. (Cnidaria: Myxosporea) infecting the alimentary tract of northern snakehead Channa argus cultivated in China

The northern snakehead Channa argus is a freshwater fish of high economic importance in Asian countries. Intensive snakehead cultivation requires the regular addition of feedwater to ensure water quality, providing an opportunity for parasite transmission. However, the parasite composition of northern snakehead is still poorly studied. In a series of investigations conducted in China, a myxosporean species was isolated from the farmed northern snakehead. It manifested with a dense formation of ellipsoidal, proliferous cysts presenting along the wall of the intestine and pyloric caeca. The microorganism inside the cyst displayed elongate, pyriform, and bivalved myxospores, with an elongated caudal appendage extending from posterior extremity of each smooth shell valve. Two pyriform polar capsules were situated at a level perpendicular to the sutural plane. Based on these observations, the present isolates was assigned to the genus Myxobilatus. However, it was morphologically distinguishable from other congeners. Moreover, the same result was obtained according to a less than 92% top genetic identity observed in pairwise comparison. Therefore, we confirmed the present species new to science and designated it as Myxobilatus channi n. sp. Histologically, plasmodia bulging toward the mucosa were confined to the circular muscle layer, leading to epithelial sloughing and necrosis of the intestinal villi. Phylogenetically, M. channi n. sp. was positioned branching from those species belonging to the family Myxobilatidae, implicating the inability of morphological taxonomy to reflect the true evolutionary relationship among myxosporeans. This study enhances the understanding of the composition of the parasite infecting the northern snakehead that will inform future scrutiny and management of the parasite infection.

Localization of relaxin-like gonad-stimulating peptide expression in starfish reveals the gonoducts as a source for its role as a regulator of spawning.

Oocyte maturation and gamete release (spawning) in starfish are triggered by relaxin-like gonad-stimulating peptide (RGP), a neuropeptide that was first isolated from the radial nerve cords of these animals. Hitherto, it has generally been assumed that the radial nerve cords are the source of RGP that triggers spawning physiologically. To investigate other sources of RGP, here we report the first comprehensive anatomical analysis of its expression, using both in situ hybridization and immunohistochemistry to map RGP precursor transcripts and RGP, respectively, in the starfish Asterias rubens. Cells expressing RGP precursor transcripts were revealed in the ectoneural epithelium of the radial nerve cords and circumoral nerve ring, arm tips, tube feet, cardiac stomach, pyloric stomach, and, most notably, gonoducts. Using specific antibodies to A. rubens RGP, immunostaining was revealed in cells and/or fibers in the ectoneural region of the radial nerve cords and circumoral nerve ring, tube feet, terminal tentacle and other arm tip-associated structures, body wall, peristomial membrane, esophagus, cardiac stomach, pyloric stomach, pyloric caeca, and gonoducts. Our discovery that RGP is expressed in the gonoducts of A. rubens proximal to its gonadotropic site of action in the gonads is important because it provides a new perspective on how RGP may act as a gonadotropin in starfish. Thus, we hypothesize that it is the release of RGP from the gonoducts that triggers gamete maturation and spawning in starfish, while RGP produced in other parts of the body may regulate other physiological/behavioral processes.

Phylogeny, Distribution, and Biology of Pygmy Whitefish (Prosopium coulterii) in the Beringia Region (Chukotka)

The pygmy whitefish Prosopium coulterii (C. H. Eigenmann &amp; R. S. Eigenmann, 1892) is a freshwater fish with a highly disjunct distribution ranging from the middle part of North America to Chukotka. There is still no consensus regarding its phylogeny and dispersal history due to limited information from the Chukotkan part of the range. We investigated 22 lakes over Chukotka and found a much broader distribution than it was previously thought. Pygmy whitefish was found to be a common species in the lakes that belong to rivers draining into the Arctic. Cytochrome B, cytochrome oxidase subunit 1, and ATP synthase F0 subunit 6 mitochondrial sites were analyzed from 25 samples to reconstruct the phylogenetic history of pygmy whitefish. Two haplogroups belonging to the east and west Chukotkan ranges were identified; both groups are closely related to Alaskan pigmy whitefish and distant from the Cascadia-Mackenzie (Peace) populations. Combining the distribution patterns, phylogenetic network topology, and the contemporary knowledge on the glaciation history of the region, we suggest a possible colonization pathway over Beringia region and beyond it. The basic biological characteristics (fork length, number of gill rakers, and pyloric caeca, age structure, and feeding) are also presented to characterize the populations over the investigated range.

An atlas of plasma-accessible carbonic anhydrase availability in the model teleost, the rainbow trout.

The unique teleost oxygenation system that permits enhanced oxygen unloading during stress comprises three main characteristics: pH-sensitive haemoglobin, red blood cell (RBC) intracellular pH (pHi) protection, and a heterogeneous distribution of plasma-accessible carbonic anhydrase (paCA). A heterogeneous distribution of paCA is essential; its presence permits enhanced oxygen unloading during stress, while its absence at the gills maintains conditions for oxygen uptake by pH-sensitive haemoglobins. We hypothesised that paCA would be absent in all four gill arches, as has been previously indicated for arch two, and that paCA would be present in all other tissues. Through a suite of biochemical and molecular methods, we confirmed the absence of paCA from all four arches. We also found evidence for paCA in nine other tissues and a lack of paCA availability in the stomach. Expression was highly variable between tissues and suggests these differences may be associated with their respective metabolic activities. Additionally, we analysed the specific CA-IV isoform expressed within each tissue and showed almost complete separation of expression between tissues; CA-IVa was detected in the heart, brain, anterior intestine, and liver, whereas CA-IVb was detected in all intestine sections, pyloric caeca, kidney, and white muscle. This adds to a growing collection of work suggesting CA-IVa and b play divergent roles in gas exchange and ion/acid-base balance, respectively. The current study represents the first comprehensive atlas of paCA availability within the circulatory system of the model teleost, rainbow trout, and fills important gaps in our knowledge of this unique oxygenation system.

Histochemical research of enzymes involved in cellular digestion in the digestive tract of tub gurnard, Chelidonichthys lucerna.

The tub gurnard Chelidonichthys lucerna (Linnaeus, 1758), Triglidae, is an opportunistic, demersal carnivorous fish. Data on the digestive enzymes of tub gurnard have not been reported in the literature. Therefore, the aim of this research was to investigate the distribution and intensity of alkaline phosphatase, acid phosphatase, non-specific esterase, and aminopeptidase in the digestive tract of tub gurnard. To investigate data about those enzymes tissue samples of the esophagus, anterior and posterior part of the stomach, pyloric caeca, anterior, middle and posterior part of the intestine proper, and rectum were taken. Azo-coupling methods were used to detect the enzymatic reactions. The intensities of the reactions were measured using ImageJ software. Alkaline phosphatase, acid phosphatase, and non-specific esterase activities were found in all parts of the digestive tract. The brush border of the pyloric caeca and intestine proper were the main sites of alkaline phosphatase reaction, with intensity decreasing toward the posterior parts of the digestive tract. The high intensities of acid phosphatase were found in the epithelium of the anterior part of the stomach, pyloric caeca, anterior part of the intestine proper, and in the rectum. The intensity of non-specific esterase was mainly increased from the anterior to the posterior parts of the digestive tract. Aminopeptidase activity was found in the esophagus, pyloric caeca, and intestine proper. Our results suggest that the entire digestive tract of the tub gurnard is involved in the digestion and absorption of dietary components.

Effects of Dietary Vegetable Oil Mixtures including Soybean Oil on Intestinal Oxidative Stress in Gilthead Sea Bream (Sparus aurata).

Fish oil is commonly replaced by vegetable oils in sea bream diets, but little is known about their effects on intestinal health regarding oxidative stress biomarkers. The negative effects of lipid peroxidation on digestive mucosa could have consequences in animal nutrition and welfare. In this study, five isonitrogenous (46%) and isolipidic (22%) diets with 75% of vegetable oils inclusion were evaluated: soybean oil (S) alone or different mixtures containing soybean oil with linseed (SL), linseed and rapeseed (SLR), linseed and palm (SLP), and linseed, rapeseed, and palm (SLRP). Gilthead sea bream juveniles were fed twice a day for 18 weeks. Pyloric caeca and proximal intestine samples were collected 24 h post feeding for lipid peroxidation (LPO), antioxidant enzyme activities (SOD, CAT, GPx, GST, and GR) and gene expression analyses. Pyloric caeca presented larger unhealthy changes in oxidative status than proximal intestine. Although SL-fed fish showed the highest antioxidant activities, they were unable to cope with LPO that in pyloric caeca was 31.4 times higher than in the other groups. Instead, SLP fish presented the best oxidative status, with low LPO levels, antioxidant enzyme activities, and gene expression. In summary, between the vegetable oils dietary mixtures tested, SPL would maintain better intestinal health.

First insights about orexigenic activity and gastrointestinal tissue localization of ghrelin from Corvina drum (Cilus gilberti)

The croaker Cilus gilberti commonly known as Corvina drum is considered a target marine species for the diversification of Chilean aquaculture. To optimize culture conditions, molecular markers for appetite regulation must be examined. Ghrelin, a gastrointestinal peptide, plays a stimulatory role in the food intake of mammals and teleost fish. Nevertheless, even though the appetite-controlling system is considered relatively well conserved among vertebrates, the bioactivity of these molecules should be analyzed in each fish species. Therefore, this study aimed to investigate the expression and orexigenic ability of C. gilberti ghrelin. After the pre and postprandial period, the stomach expression of ghrelin mRNA in juvenile C. gilberti was analyzed. The coding sequence of C. gilberti ghrelin was used to identify the mature peptide and then chemically synthesized. The orexigenic ability of acylated ghrelin (cgGhre) and non-acylated (D-cgGhre) ghrelin was tested in C. gilberti juveniles. Moreover, the blood and the gastrointestinal location of synthetic ghrelin after intraperitoneal injection were measured. The results showed that the stomach has the highest expression of ghrelin mRNA, and that ghrelin levels increased in the preprandial period and diminished after it. There were no differences in the secondary structure of D-cgGhre compared to cgGhre but the peptide with the serine acylation stabilized its unordered conformation. However, the highest cumulative feed intake occurred in fish intraperitoneally injected with cgGhre. In addition, synthetic ghrelin was maintained in the C. gilberti blood until 8 h post-injection (hpi). Finally, biotinylated ghrelin allowed localizing the synthetic peptide in digestive tissue, mainly in the stomach and pyloric caeca. The mRNA expression of the growth hormone secretagogue receptor (GHS-R), also known as the ghrelin receptor, in gastrointestinal organs supports the idea of peripheral orexigenic regulation in these tissues. In conclusion, results suggest that C. gilberti ghrelin conserves the orexigenic ability reported in other teleost fish with a regulatory role in the gastrointestinal tract (GIT) of the Corvina drum. This is the first report demonstrating the uptake and distribution of a small orexigenic peptide in the digestive tissues of a South American sciaenid. Although ghrelin is a promising molecular marker for feed intake analysis in C. gilberti culture, further research is needed to continue evaluating the effects of aquaculture practices on peripheral appetite signalizer.

Morphology, Histology, and Histochemistry of the Digestive Tract of the Marbled Flounder Pseudopleuronectes yokohamae

This study investigated the morphological, histological, and histochemical characteristics of the digestive tract of the marbled flounder (Pseudopleuronectes yokohamae). The relative length of the gut of the marbled flounder digestive tract was 1.54 ± 0.10 (n = 20), and it had a simple stomach and 6-9 pyloric caeca. The mucosal folds of the marbled flounder digestive tract exhibited a general branched morphology. The thickness and mucosal fold length of the intestinal muscularis externa showed similar aspects in all areas. The thickness of the intestinal muscularis externa was the thickest in the posterior intestine portion, and the length of mucosal folds was the longest in the anterior intestine portion. It was indicated that food digested by gastric acid in the stomach moves to the anterior portion (including pyloric caeca) and mid portion of the intestine, ensuring effective stimulation of cholecystokinin (CCK)-producing cells. In addition, the distribution pattern of CCK-producing cells in the intestine was very similar to that of mucus-secreting goblet cells. The CCK-producing cells and goblet cells in the marbled flounder were well-adapted to promote optimal control of the digestive process. Based on the morphological and histochemical studies, it was concluded that the marbled flounder displays a digestive tract comparable to that of fish species with carnivorous habits.

Responses of the gastrointestinal microbiota to the protein metabolism of pond-cultured Japanese flounder (Paralichthys olivaceus)

Protein metabolism can provide energy for various biological activities of organisms. However, there have been few studies on the succession of gastrointestinal microbiota structure during the metabolism of protein by the host. In this study, physiological and biochemical, qRT-PCR, and 16S rDNA high throughput sequencing methods were used to detect the activity characteristics of proteases and the related gene expression levels in each gastrointestinal tissue, as well as the distribution characteristics and succession of the gastrointestinal microbiota structure of pond-cultured Japanese flounder (Paralichthys olivaceus). The results showed that the activity of pepsin, trypsin, and chymotrypsin in the pyloric caecum and gut, and the relative expression levels of the related genes, increased first and then decreased, but the aspartate aminotransferase (ASP) and alanine aminotransferase (ALA) activity showed the opposite tendency. These reflected that the nutrient composition of gastrointestinal tract contents was dynamic, which caused obvious changes to the alpha diversity and structure of gastrointestinal microbiota. Lactobacillus, Acinetobacter, Bacteroides, Escherichia-Shigella, Prevotella, the genera represented by the Lachnospiraceae_NK4A136_group and MND1, Sphingomonas, Alistipes, Alloprevotella, Enterobacter, Helicobacter, Myroides, Ruminiclostridium, and Romboutsia were the main gastrointestinal microbiota based on the dominance, commonality, and colonization. The relative abundance of Lactobacillus and Acinetobacter in the three gastrointestinal tissues increased first and then decreased. According to the number of shared and dominant genera, the consistency of succession of some genera, and the increase in the similarity of microbiota structure among the three tissues, we inferred that the microbiota was affected by the gastrointestinal tract nutrient composition. Gastrointestinal microbiota genes were mainly enriched in the metabolism pathway according to the KEGG pathway, and the ratio of Firmicutes to Bacteroidetes, the representative of energy accumulation, followed an at-first increasing and then decreasing trend in each tissue. This shows that the main gastrointestinal microbiota played a synergistic role in the energy accumulation of the host. This study will provide a reference for the development of high-efficiency compound feed formulae and improve feed efficiency by regulating the gastrointestinal tract microecology for pond-cultured Japanese flounder.

Oxygenation of European seabass (Dicentrarchus labrax L.) in cages through aeration and effect on lipid metabolism.

Two groups of the same batch of European seabass were used in an industrial-scale trial in sea cages in Vorios Evoikos, Greece. For about one month, one of the two cages was oxygenated by use of compressed air injected in seawater through an AirX frame (Oxyvision A/S, Norway) at 3.5 m depth, while oxygen concentration and temperature were monitored every 30 min. The liver, gut, and pyloric ceca samples were taken from fish of both groups for measurement of gene expression of phospholipase A2 (PLA2) and hormone-sensitive lipase (HSL), and for histological analysis at the middle and end of the experiment. Real-time qPCR was performed with housekeeping genes ACTb, L17, and EF1a. The expression of PLA2 increased in pyloric caeca samples from the oxygenated cage, suggesting that aeration improved the absorption rate of dietary phospholipids (p < 0.05). Expression of HSL increased significantly in liver samples from the control cage, in comparison with the aerated cage (p < 0.05). Histological examination of sea bass samples revealed an increased fat accumulation in the hepatocytes of fish in the oxygenated cage. The results of the present study showed increased lipolysis induced by low DO levels in farmed sea bass in cages.

Identification and characterization of two long-type peptidoglycan recognition proteins, PGRP-L1 and PGRP-L2, in the orange-spotted grouper, Epinephelus coioides

Peptidoglycan recognition proteins (PGRPs) play an important role in innate immunity by recognizing components of pathogenic bacteria (such as peptidoglycan, PGN) and are evolutionarily conserved pattern recognition receptors (PRRs) in both invertebrates and vertebrates. In the present study, two long-type PGRPs (designed as Eco-PGRP-L1 and Eco-PGRP-L2) were identified in orange-spotted grouper (Epinephelus coioides), which is a major economic species cultured in Asia. The predicted protein sequences of both Eco-PGRP-L1 and Eco-PGRP-L2 contain a typical PGRP domain. Eco-PGRP-L1 and Eco-PGRP-L2 exhibited organ/tissue-specific expression patterns. An abundant expression of Eco-PGRP-L1 was observed in pyloric caecum, stomach and gill, whereas a highest expression level of Eco-PGRP-L2 was found in head kidney, spleen, skin and heart. In addition, Eco-PGRP-L1 is distributed in the cytoplasm and nucleus, while Eco-PGRP-L2 is mainly localized in cytoplasm. Both Eco-PGRP-L1 and Eco-PGRP-L2 were induced following the stimulation of PGN and have PGN binding activity. In addition, functional analysis revealed that Eco-PGRP-L1 and Eco-PGRP-L2 possess antibacterial activity against Edwardsiella tarda. These results may contribute to understand the innate immune system of orange-spotted grouper.

Effects of dietary supplementation with prebiotics and Pediococcus acidilactici on gut health, transcriptome, microbiota, and metabolome in Atlantic salmon (Salmo salar L.) after seawater transfer

BackgroundGiven the importance of gut microbiota for health, growth and performance of the host, the aquaculture industry has taken measures to develop functional fish feeds aiming at modulating gut microbiota and inducing the anticipated beneficial effects. However, present understanding of the impact of such functional feeds on the fish is limited. The study reported herein was conducted to gain knowledge on performance and gut health characteristics in post-smolt Atlantic salmon fed diets varying in content of functional ingredients. Three experimental diets, a diet containing fructo-oligosaccharides (FOS), a diet with a combination of FOS and Pediococcus acidilactici (BC) and a diet containing galacto-oligosaccharides (GOS) and BC, were used in a 10-weeks feeding trial. A commercial diet without functional ingredients was also included as a control/reference. Samples of blood plasma, mucosa and digesta were subjected to microbiota, transcriptome and metabolome profiling for evaluation of the diet effects.ResultsNo significant growth differences were observed between fish fed the supplemented diets, but FOS–BC fed fish showed significantly faster growth than the control fed fish. The microbiota results showed that the BC was present in both the digesta, and the mucosa samples of fish fed the FOS–BC and GOS–BC diets. Digesta-associated microbiota was altered, while mucosa-associated microbiota was relatively unaffected by diet. Replacing FOS with GOS increased the level of metabolites linked to phospholipid, fatty acid, carnitine and sphingolipid metabolism. Variation in metabolite levels between the treatments closely correlated with genera mainly belonging to Firmicutes and Actinobacteria phyla. The transcriptome analyses indicated diet effects of exchanging FOS with GOS on immune functions, oxidative defense and stress responses. No significant diet effect was observed on intestinal inflammation in the pyloric caeca or in the distal intestine, or on lipid accumulation in the pyloric caeca.ConclusionsDietary supplementation with BC induced moderate effects on the microbiota of the digesta, while the effects of replacing FOS with GOS were more marked and was observed also for nutrient metabolism. Our data indicates therefore that the quality of a prebiotic may be of great importance for the effects of a probiotic on gut microbiota, function, and health.

Effects of dietary lipid level and environmental temperature on lipid metabolism in the intestine and liver, and choline requirement in Atlantic salmon (Salmo salar L) parr.

Choline was recently established as an essential nutrient for Atlantic salmon at all life stages. Choline deficiency is manifested as an excessive accumulation of dietary fat within the intestinal enterocytes, a condition known as steatosis. Most of today's plant-based salmon feeds will be choline-deficient unless choline is supplemented. Choline's role in lipid transport suggests that choline requirement may depend on factors such as dietary lipid level and environmental temperature. The present study was therefore conducted to investigate whether lipid level and water temperature can affect steatosis symptoms, and thereby choline requirement in Atlantic salmon. Four choline-deficient plant-based diets were formulated differing in lipid level of 16, 20, 25 and 28 % and fed to salmon of 25 g initial weight in duplicate tanks per diet at two different environmental temperatures: 8 and 15 °C. After 8 weeks of feeding, samples of blood, tissue and gut content from six fish per tank were collected, for analyses of histomorphological, biochemical and molecular biomarkers of steatosis and choline requirement. Increasing lipid level did not affect growth rate but increased relative weight and lipid content of the pyloric caeca and histological symptoms of intestinal steatosis and decreased fish yield. Elevation of the water temperature from 8 to 15 °C, increased growth rate, relative weight of the pyloric caeca, and the histological symptoms of steatosis seemed to become more severe. We conclude that dietary lipid level, as well as environmental temperature, affect choline requirement to a magnitude of importance for fish biology and health, and for fish yield.