Intestine Of Fish Research Articles

Dietary African Yam Bean Meal (Sphenostylis sternocarpa) as a Complementary Substitute for Soybean Meal in African Catfish (Clarias gariepinus) Fingerlings: Effect on Intestinal Histology and Zootechnical Performance

Background: The effects of soybean meal replacement with African yam bean meal on the intestinal histology and zootechnical performance of African catfish, Clarias gariepinus fingerlings was assessed in this study. One hundred and eighty C. gariepinus fingerlings weighing 13.62±0.12g were randomly distributed into plastic tanks at ten fish per tank in triplicate and fed six rations (treatments) representing graded replacement levels of soybean with African yam bean for 70 days. Soybean meal was replaced with African yam bean (AYB) at 0, 20, 40, 60, 80 and 100% denoted as the control T1 (0%), T2 (20%), T3 (40%), T4 (60%), T5 (80%) and T6 (100%) respectively. Weekly weighing of fish was done and data collected was subjected to statistical analysis. Zootechnical performance was based on growth performance and nutrient utilization efficiency. Results: After the feeding trials, tissue samples from the intestines were removed by dissection for histological study. Tissue sections were compared after examination under the microscope for differences in the morphology of the tissues. The histology of the intestine of fish fed African yam bean meal included diets showed apparently normal intestinal villi and enterocytes in T2, T3 and T4. Histology of the intestine of C. gariepinus in T6 had disorganized enterocytes which induced enteritis in the fish. The result on growth performance and nutrient utilisation showed that body weight gain, specific growth rate and feed conversion ratio were significantly different from each other (P< 0.05). The best feed conversion ratio was recorded in the control. Conclusions: This study showed that African yam bean can replace soybean up to 60% in the diet of African catfish, Clarias gariepinus for required growth without any negative effect on the gut histology of the fish.

Comparative Study of Electrophoretic Patterns of Protein Sub Units in Various Tissues of Two Fresh Water Fishes (Heteropneustes fossilis and Labeo rohita) Through Gel Electrophoresis

The present investigation is determine the comparative study of electrophoretic patterns of protein sub units in two different fishes i.e. Heteropneustes fossilis and Labeo rohita. All the tissues were examined on 7.5% SDS-PAGE. In this investigation we observed gill, liver, intestine, muscle and brain tissues of both fishes. In this Gill and Muscle tissues of two fishes exhibits highest protein bands (10 and 7 respectively). The lowest bands are observed in intestine in both fishes(7,5 respectively).In this investigation we observed homology in protein bands with minor variations.

Transcriptome Sequencing Reveals Effects of Artificial Feed Domestication on Intestinal Performance and Gene Expression of Carnivorous Mandarin Fish (Siniperca chuatsi) and Related Mechanisms.

Mandarin fish (Siniperca chuatsi) is a voracious carnivorous species, usually consuming only live bait fish, but dietary acclimation enables it to accept artificial feed. However, the effects of dietary acclimation on intestinal performance and gene expression in mandarin fish and related mechanisms remain largely unknown. Therefore, this study investigated the effects of artificial feed on intestinal physicochemical and biochemical performance and gene expression in mandarin fish. Mandarin fish were sampled on day 10 after feeding with live dace (LD), at day 40 after subsequent feeding with dead dace plus artificial feed (DD + AF) from day 11 to day 40, and at day 90 after continuous feeding with artificial feed (AF) alone from day 41 to day 90 for transcriptome sequencing. The biochemical analysis results indicated that artificial feed significantly increased the activity of antioxidant enzymes glutathione peroxidase and superoxide dismutase in the intestine, liver, and stomach. Histological analysis demonstrated intestinal damage in mandarin fish fed with artificial feed. The GO and KEGG enrichment analyses indicated that the DEGs in AF vs. DD + AF were significantly enriched in the pentose phosphate pathway, and the DEGs in AF vs. LD were mainly significantly enriched in glycolysis/gluconeogenesis and PPAR signaling pathways. Nineteen feed acclimation-related key genes such as gene pfkfb4a and scd were identified in the intestine and found to exhibit upregulated expressions. These results revealed that artificial feed domestication enhanced the antioxidant capacity of the mandarin fish intestine and reduced hepatic lipid deposition by upregulating the related gene expression of mandarin fish and that the regulation of carbon metabolisms, including sugar, lipid, and steroid metabolisms, might be fundamental mechanisms for mandarin fish to acclimatize to dietary changes. These findings provide novel insights into the feed acclimation mechanism of mandarin fish, holding implications for promoting large-scale artificial feed aquaculture of mandarin fish and improving economic efficiency.

Cadmium Pollution Deteriorates the Muscle Quality of Labeo rohita by Altering Its Nutrients and Intestinal Microbiota Diversity.

The detrimental effects of cadmium (Cd), a hazardous heavy metal, on fish have triggered global concerns. While the ecotoxicity of Cd on fish has been investigated, the impact of Cd on muscle quality and its correlation with the gut microbiota in fish remains scarce. To comprehensively uncover Cd effects based on preliminary muscle Cd deposition, relevant studies, and ecological Cd pollution data, we exposed Labeo rohita to Cd under concentrations of 0.00 (control), 0.05, and 0.40mg/L for 30days and assessed fish health, muscle quality, and intestinal bacterial diversity. We observed significant Cd bioaccumulation in the fish muscle and intestine at 0.40mg/L treatment, adversely impacting fish health with lower growth indices, higher mortality, behavioral aberrations, and clinical anomalies. More interestingly, Cd exposure decreased muscle quality by reducing nutrient levels, including fat, protein, iron, zinc, mono and polyunsaturated fatty acids, and increasing free amino acids and saturated fatty acids. Elevated oxidative stress markers, including total superoxide dismutase (T-SOD), catalase (CAT), and hydrogen peroxide (H2O2), were detected in the muscles, indicating degraded quality as a result of damage to cellular structures including proteins, lipids, and DNA. Simultaneously, we found Cd exposure altered fish intestinal microbial diversity, impairing muscle nutrient assimilation, thereby influencing muscle quality. Functional predictions suggested a decrease in pathways related to fermentation and chemoheterotrophy in the exposed groups. Overall, this study highlights how Cd toxicity jeopardizes fish health and deteriorates muscle quality which needs to be addressed for human benefit.

Integrative RNA, miRNA, and 16S rRNA sequencing reveals immune-related regulation network for glycinin-induced enteritis in hybrid yellow catfish, Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂.

Glycinin-induced foodborne enteritis is a significant obstacle that hinders the healthy development of the aquatic industry. Glycinin causes growth retardation and intestinal damage in hybrid yellow catfish (Pelteobagrus fulvidraco ♀ × Pelteobagrus vachelli ♂), but its immune mechanisms are largely unknown. In the current study, five experimental diets containing 0% (CK), 1.74% (G2), 3.57% (G4), 5.45% (G6), and 7.27% (G8) immunological activity of glycinin were fed to juvenile hybrid yellow catfish to reveal the mechanism of the intestinal immune response to glycinin through RNA and microRNA (miRNA) sequencing and to explore the interrelation between immune molecules and intestinal microbiota. The results demonstrated that glycinin content in the posterior intestine increased significantly and linearly with the rise of dietary glycinin levels. More than 5.45% of dietary glycinin significantly reduced the nutritional digestion and absorption function of the posterior intestine. Notably, an obvious alteration in the expression levels of inflammatory genes (tnf-α, il-1β, il-15, and tgf-β1) of the posterior intestine was observed when dietary glycinin exceeded 3.57%. Sequencing results of RNA and miRNA deciphered 4,246 differentially expressed genes (DEGs) and 28 differentially expressed miRNAs (DEmiRNAs) between the CK and G6 groups. Furthermore, enrichment analysis of DEGs and DEmiRNA target genes exhibited significant responses of the MAPK, NF-κB, and WNT pathways following experimental fish exposure to 5.45% dietary glycinin. Additionally, at the level of 3.57% in the diet, glycinin obviously inhibited the increase of microbiota, especially potential probiotics such as Ruminococcus bromii, Bacteroides plebeius, Faecalibacterium prausnitzii, and Clostridium clostridioforme. In sum, 5.45% dietary glycinin through the MAPK/NF-κB/WNT pathway induces enteritis, and inflammatory conditions could disrupt micro-ecological equilibrium through miRNA secreted by the host in hybrid yellow catfish. This study constitutes a comprehensive transcriptional perspective of how intestinal immunity responds to excessive glycinin in fish intestines.

Effects of Different Preservation Methods on the Structure and Diversity of Intestinal Microbiota of Marine Fishes.

The fish intestine is a complex ecosystem where microbial communities are dynamic and influenced by various factors. Preservation conditions during field collection can introduce biases affecting the microbiota amplified during sequencing. Therefore, establishing effective, standardized methods for sampling fish intestinal microbiota is crucial. This study used hybrid groupers (Epinephelus fuscoguttatus♀ × E. lanceolatus♂) to examine the effects of six preservation methods: dry ice (1 day), dry ice (1 day) followed by -80°C storage (5 days), liquid nitrogen (1 day), liquid nitrogen (1 day) with subsequent -80°C storage (5 days), refrigeration at 4°C (3 days), and freezing at -20°C (3 days), with fresh samples as controls. High-throughput 16S rRNA sequencing assessed microbial diversity, community structure, dominant species, and OTU abundance across treatments. Results indicated that dry ice and liquid nitrogen methods, especially with -80°C storage, had minimal impact on microbial diversity and structure. Compared to other preservation methods, refrigeration at 4°C and freezing at -20°C may result in suboptimal reproducibility and altered community structure, particularly affecting rare microbial taxa. This study underscores the need for standardized preservation techniques to ensure accurate fish intestinal microbiota analysis and provides a foundation for future research.

Sublethal Urea Exposure in Nile Tilapia: Morphological, Behavioural, and Histological Alteration.

The pace of research efforts has been extraordinarily accelerated across the globe to address the contamination issues caused by pesticides, and fertilizers, especially in the aquatic ecosystem. The sole aim of this study was to assess the effect of urea on Nile Tilapia (Oreochromis niloticus). For this purpose, the fish fingerlings were exposed to increasing concentrations of urea such as 0, 1, 2.5, 5, 10, 20, and 40 g/l for 72 hr. Survival analysis suggested a strong correlation between the increasing doses of urea and the mortality rate among tested fingerlings. This study reported remarkable morphological, and behavioural alternation such as increased operculum movement, bottom-dwelling, lethargy, secretion of mucus, reduction in food intake, and bleeding in the fin and around the mouth in the treated group. Haematological analysis revealed that a significant reduction in RBC count and Hb along with an increase in WBC number is associated with urea toxicity. Our study showed a significant rise in glucose concentration upon urea toxicity in Nile tilapia fingerlings for the first time, emphasizing the adverse effect of fertilizers on carbohydrate metabolism. Significant rises in the enzymatic activity such as alanine aminotransferase (ALT), alkaline phosphatase (ALP), and aspartate aminotransferase (AST) upon urea treatment emphasize the possibilities of liver damage, biliary obstruction, and abnormal glucose metabolism. Histological analysis of urea-treated fish compared to normal fish revealed that urea toxicity drastically altered the tissue architecture of fish's gills, eyes, intestine, and stomach. As the visual systems of mammals and fish resemble in more aspects, our findings may be useful in understanding the impact of pollutants on sensory organs concerning humans. We conclude that our findings highlight the importance of urea toxicity on Nile tilapia fingerlings and invite multidisciplinary research to uncover molecular mechanisms underlying urea toxicity.

An oral probiotic vaccine loaded by Lactobacillus casei effectively increases defense against GCRV infection in grass carp.

For a long time, grass carp culture in China has been severely affected by Grass Carp hemorrhagic disease caused by Grass Carp Reovirus (GCRV). At present, vaccines have been widely used for protecting aquatic organisms against infectious diseases, among which oral immunization with Lactobacillus casei is safe and highly effective. This vaccination route has the advantages of easy administration and noninvasive delivery. In this study, the recombinant LC-pVE5523-VP5 was constructed by using the outer capsid protein VP5 of GCRV as the immunogen and pVE5523 as the secretory expression vector. The bacterial powder was prepared from fermented broth by using the vacuum freeze-drying technology. The dried bacterial powder was subsequently mixed with feed and then pressed to pellets. After oral administration of the feed mixed with the recombinant L.casei powder, the expression of the immune-related genes (IFN I, IgM et al.) in grass carp was upregulated significantly. With the increased duration of oral immunization period, serum IgM level was also increased in grass carp. The survival analysis was carried out on the basis of grass carp in response to GCRV challenge. The result showed that the survival rate in the immunized group (74%) was significantly higher than that in the control group (35%). The amount of virus replication was also investigated in vaccine-treated fish. The result suggested that the virus content in fish tissue was also significantly less than that of the non-immunized group. The LC-pVE5523-VP5 was still present in the fish intestines 15days after vaccination. These results indicated that the oral LC-pVE5523-VP5 can effectively protect grass carps from GCRV infection.

A Bacterial Analysis of Some Fish Caught in the Bingöl Region of the Murat River

The present study aimed to investigate the microbial diversity of three fish species (Chondrostoma regium, Capoeta trutta and Cyprinion macrostomum) from the Bingöl region of the Murat River. Gill and intestinal samples were obtained from a total of 52 fish. Conventional microbial analysis methods were employed. Bacterial identification was conducted through the utilisation of biochemical tests. A total of 285 bacteria (117 from gills and 168 from intestines) belonging to 10 genera were isolated and identified. The most prevalent species identified in the gills and intestines of fish were Escherichia coli (24.58%), Enterobacter aerogenes (26.30%), Staphylococcus sp. (14.22%) and Aeromonas sp. (12.28%). It is imperative to implement a programme of continuous monitoring of the bacterial parameters of the existing water system, in order to ensure the continued safety of fish and the public.

Fish Waste Compost - A Fertilizer for Organic Agriculture

Fish markets produce a large amount of fish waste such as fish head, gut, intestine, fines, bones and scales that are generally dumped in the river or land-filling areas causing great intuitive pollution to the environment. Such impulsively growing contamination can be mitigated and checked though waste management in the form of organic composting. This study investigates the potential of fish waste compost as a sustainable organic fertilizer by converting fish waste, including gut, head, skin, bones, and fins, into compost using sawdust, banana and jaggery as supplementary materials. The matured compost was then analyzed for nutrient content and maturity through physical, sensory, biological, and chemical tests. Results showed that the compost, reduced to 70% of its original volume, had significant nutrient content with a C:N ratio of 28.6:1, a pH of 6.80, and an electrical conductivity of 1.45 dS/m. Biological tests demonstrated high germination rates, indicating non-phytotoxicity. Fish waste containing 10.56, 2.12, 0.82 and 0.10 percents of C, N, P and K respectively can be converted into an effective organic fertilizer which can enhance soil fertility. This approach not only addresses waste management but also offers a viable solution for recycling fish waste into valuable agricultural resources.

Comparative analysis of intestinal structure, enzyme activity, intestinal microbiota and gene expression in different segments of pufferfish (Takifugu Obscurus)

The structure of fish intestines does not have a clear regional division, while the function of the intestines may be related to their structure. Therefore, in this study, the delimitation of intestinal segments in pufferfish (Takifugu obscurus) was achieved by morphological analysis. Subsequently, enzyme activity, intestinal microbiota, and gene expression were examined to compare the differences among the pufferfish various segments. According to four morphological parameters: height of mucosa folds (HF), width of mucosa folds (WF), thickness of muscularis (TM), and cross-sectional area (CSA), the pufferfish's intestine was divided into anterior intestine (AI), middle intestine (MI), and posterior intestine (PI). The activity levels of amylase, lipase, and trypsin in the AI and MI were significantly higher than these in the PI. According to the analysis of 16S rDNA, the dominant microbiota at the phylum level in the different segments were Epsilonbacteraeota, Spirochaetes, and Proteobacteria. At the genus level, there were variations observed in the relative abundance of Brevinema, Mycobacterium, Bradyrhizobium, and Microvirga. α diversity analysis revealed that the richness indexes (Ace and Chao1) were the lowest in the MI, while β diversity analysis revealed significant difference in intestinal microbial community composition among the three intestinal segments. Furthermore, RNA-Seq was used to identify differential expression genes (DEGs) and biological pathways among the different intestinal segments. The DEGs between the AI and MI were enriched in pancreatic secretion and protein digestion and absorption, those between AI and PI were involved in ascorbate and aldarate metabolism and glutathione metabolism, and those between MI and PI were involved in steroid biosynthesis, fat digestion and absorption, vitamin digestion and absorption, and glycine, serine and threonine metabolism. In conclusion, the presented results compare and analyze the differences in various intestinal segments of pufferfish, which will be conductive to future exploration of the functions of these different segments.

Commensal and Pathogenic Bacteria Associated with Farmed Rainbow Trout (Oncorhynchus mykiss Walbum) and Aquaculture Environment

The bacterial microflora associated with farmed rainbow trout (Oncorhynchus mykiss Walbaum) and its aquaculture environment was characterized. The counts of commensal, indicator and pathogenic bacteria were determined and bacterial colonies were characterized. The mean mesophilic counts were 4.5 log CFU g -1 and 7.6 log CFU g -1 in skin with muscle and intestine respectively. Significantly high densities of faecal coliform, E. coli and Enterococci was detected in pond sediment, fish intestine and feed when compared to pond water and trout tissues. A total of 110 randomly selected isolates from TSA were identified and characterized. Of the mesophiles, 70–75% were aerobic Gram-negative bacteria, both motile and non-motile, and members of the Enterobacteriaceae family. The skin microflora of trout was dominated by Gram-negative aerobic rods belonging to Enterobacteriaceae, Aeromonadaceae, Pseudomonas/ Shewanella, Moraxella, Acinetobacter and Flavobacterium. Psychrotrophic bacterial isolates of the genera Pseudomonas, Morganella, Hafnia were identified in trout. Pathogenic bacteria such as Clostridium botulinum, Yersinia enterocolitica could not be detected. However, Aeromonas hydrophila, A. veronii biovar sobria, A. veronii biovar veronii were prevalent in farmed trout. Presence of bacterial pathogens in the trout farm envisages a strict hygienic handling and processing of fish from such culture systems for ensuring public health safety.

Machine Learning-Based Classification of Malnutrition Using Histological Biomarkers of Fish Intestine: Preliminary Data

The gut is the first organ to contact food, and it is often the target of nutrition studies performed on aquaculture fish. Histological analysis reveals morphological changes in fish intestines caused by ingredients in formulated feeds. However, this type of analysis is mainly based on a semi-quantitative approach, often restricted to specialized researchers, and may provide inconsistent results between studies. This study addresses these limitations by combining semi-quantitative and quantitative features to characterize the anterior, intermediate, and distal sections of the intestine of meagre (Argyrosomus regius) subjected to different nutritional status. Collected data were used to build machine learning models, select the most accurate ones, and identify key features for predicting malnutrition. Logistic regression, support vector machines, and ensemble stacking performed best across all intestinal sections. Combining semi-quantitative and quantitative features yielded the best predictions, with villi number, density and area, and goblet cell count being the most crucial for the classification task. When considering the distal intestine alone, semi-quantitative features outperformed quantitative ones. The intermediate section of the intestine showed the best model accuracy, indicating higher sensitivity to nutritional changes. These results demonstrate the potential of machine learning models to streamline histomorphological analyses to evaluate nutritional status, making them more accessible and standard across users.

Comprehensive transcriptomic, proteomic, and intestinal microbiota analyses of largemouth bass (Micropterus salmoides) intestines reveal new insights into immune responses to Aeromonas hydrophila infection

This study investigates the immune responses of largemouth bass (Micropterus salmoides) to infection by Aeromonas hydrophila, a pathogen responsible for significant economic losses in freshwater aquaculture due to bacterial enteritis. We employed transcriptomic sequencing, label-free LC-MS/MS quantitative proteomics, and 16S RNA sequencing to evaluate the transcriptomic, proteomic, and intestinal microbiota changes in infected fish compared to healthycontrols. Each fish (approximately 60 g) in the infection group was injected with 0.5 ml of an A. hydrophila suspension (1.0 × 108 CFU/mL), while the control group received 0.5 ml of phosphate buffer. Samples were collected 72 h post-injection, with three biological replicates made from an equal mix of tissue samples from six fish each. A total of 1666 differentially expressed genes (DEGs) and 2477 differentially expressed proteins (DEPs) were identified. Integrated analysis revealed that the up-regulated DEGs/DEPs in the intestines of infected largemouth bass were primarily associated with immune-related pathways including "antigen processing and presentation", "MAPK signaling pathway", "ECM-receptor interaction", and "leukocyte transendothelial migration". Notable upregulated immune-related proteins included complement or antigen-presenting proteins like complement C1, complement C3, complement C6, ɑ-2-macroglobulin, laminin, serotransferrin, leukocyte cell-derived chemotaxin-2, immunoglobulin C1-set domain-containing protein, and the MHC class I alpha antigen. 16S RNA sequencing indicated a significant increase in Proteobacteria and a decrease in Fusobacteria in the intestines of infected fish compared to controls. Collectively, these findings demonstrate that A. hydrophila infection significantly alters gene and protein expression as well as intestinal microbiota in largemouth bass, providing insights into their immune defense mechanisms against infection.

IDENTIFIKASI BENTUK DAN KELIMPAHAN MIKROPLASTIK PADA IKAN KAKAP PUTIH (Lates calcarifer) DAN IKAN KEMBUNG (Rastrelliger) DI PERAIRAN PANTAI DEPOK

Microplastics are plastic particles < 5 mm in size from large plastic fragments, industrial waste, and household products (microbeads). Some microplastics come from rivers that flow into ocean which can threaten marine biota and are vulnerable to consumption by marine organisms because they are considered foods. Microplastics have spread widely in Indonesia seas, one of which is Depok Beach, Yogyakarta. White snapper and mackerel are two types of fish often consumed by tourists and local people in the Depok Beach. This research aims to identify the form of microplastics and their content in mackerel and white snapper. This research method includes three stages, namely 1) taking samples of white snapper and mackerel from the fish's stomach, intestines and gills, 2) testing samples using the National Oceanic and Atmosphere Administration (NOAA) method for analyzing microplastics in the marine environment and FTIR to determine chemical compound groups in microplastics. The results of microscope observations showed that the forms of microplastics found in fish were fibers, fragments, pellets and films. For three months of data collection, the results of increasing microplastics in mackerel each month were 28.74% in fiber, 14.96% in fragment, 17.04% in film and 20% in pellet with the largest abundance value being 430 particles/gram in fragment. The results of increasing microplastics in white snapper each month were 5.93% in fiber, 20.84% in fragment, 27.60% in film and 29.41% in pellet with the largest abundance value being 248 particles/gram in fragment.

Evaluation of biofloc system effects on water quality, growth, innate immunity, physiological status, and immune- and growth-related gene expressions in early growth stages of thin-lipped mullet (Liza ramada)

A 90-day experiment was carried out to study the influence of biofloc system on water quality, growth, feed utilization, survivability, bacteria in fish gut, and physiological and immunological responses of thin-lipped mullet (Liza ramada). Two treatments, clear water (CW) and biofloc (BFS), were each designed in triplicates. Both treatments were stocked with Liza ramada (mean weight of 1.18 ± 0.02 g). BFS group showed the highest final body weight, weight gain, average daily weight gain, and specific growth rate, the lowest feed conversion ratio, and the highest protein efficiency ratio and survivability. The proximate analysis of biofloc samples showed that percent crude protein and lipid were 26.17 and 7.75% respectively with the presence of essential minerals required for fish growth. The total body chemical composition of fish demonstrated improved crude protein and fat in Liza ramada stocked in BFS compared to CW. The highest total bacterial count and Bacillus number were recorded in the intestine of fish kept under BFS. Protease, lipase, and amylase levels significantly increased in fish stocked in BFS. The highest antioxidant activity was observed in fish kept under BFS treatment, while cortisol, alanine aminotransferase, and serum aspartate aminotransferase showed the lowest activity. Significantly high serum total protein, serum albumin, serum globulin, phagocytic activity, lysozymes, respiratory burst activity, and immunoglobulin M were observed in fish raised in BFS compared to CW. The intestinal histomorphometry examination showed a significantly high villi length and width, crypt depth, high number of intraepithelial lymphocytes, and goblet cells in BFS group. BFS resulted in a significantly up-regulation of the immune genes in the liver (IL-1β, TNF-α, IL-8, and IL-10) and the growth-related genes in the liver (IGF-1 and GH) compared to CW treatment. These results revealed that applying biofloc system in the rearing of Liza ramada resulted in many advantages including growth improvement, high survivability, enhanced activity of digestive enzymes, antioxidant system, immunological response, gut health, and decreased stress enzymes.

Intestinal DHA-PA-PG axis promotes digestive organ expansion by mediating usage of maternally deposited yolk lipids

Although the metabolism of yolk lipids such as docosahexaenoic acid (DHA) is pivotal for embryonic development, the underlying mechanism remains elusive. Here we find that the zebrafish hydroxysteroid (17-β) dehydrogenase 12a (hsd17b12a), which encodes an intestinal epithelial-specific enzyme, is essential for the biosynthesis of long-chain polyunsaturated fatty acids in primitive intestine of larval fish. The deficiency of hsd17b12a leads to severe developmental defects in the primitive intestine and exocrine pancreas. Mechanistically, hsd17b12a deficiency interrupts DHA synthesis from essential fatty acids derived from yolk-deposited triglycerides, and consequently disrupts the intestinal DHA-phosphatidic acid (PA)-phosphatidylglycerol (PG) axis. This ultimately results in developmental defects of digestive organs, primarily driven by ferroptosis. Our findings indicate that the DHA-PA-PG axis in the primitive intestine facilitates the uptake of yolk lipids and promotes the expansion of digestive organs, thereby uncovering a mechanism through which DHA regulates embryonic development.

Nano-Bacillus amyloliquefaciens as a dietary intervention in nile tilapia (Oreochromis niloticus): Effects on resistance to Aeromonas hydrophila challenge, immune-antioxidant responses, digestive/absorptive capacity, and growth

The present investigation proposed an innovative trial at the probable beneficial effects of nano-Bacillus amyloliquefaciens (NBA) dietary incorporation on the Nile tilapia (Oreochromis niloticus). The investigation included the impact on the growth, digestive functions, immune-antioxidant indices, and resistance to Aeromonas hydrophila challenge. A total of 135 fish (35.14 ± 0.12 g) were equally allocated into three groups (45 fish/group; 15 fish/replicate) in triplicates for 70 days. The control, NBA2, and NBA4 groups were fed basal diets enriched with 0, 102, and 104 CFU/kg NBA, respectively. Following the feeding experiment, all experimental groups were injected with 0.1 mL (1.5 × 106) A. hydrophila, and the fish mortalities were observed for 14 days. The outcomes showed that dietary NBA (NBA4 followed by the NBA2 diet) augmented the growth variables (final body weight, total weight gain, and specific growth rate) and condition factor and declined the feed conversion ratio. The intestinal digestive enzyme (amylase and lipase) and growth hormone levels were increased and the serum glucose level was decreased by dietary NBA. Furthermore, NBA diets enhanced the immune (total protein, globulin, lysozyme, complement 3, myeloperoxidase, and phagocytic activity) and antioxidant (superoxide dismutase, catalase, and total antioxidant capacity) parameters. The intestinal histology revealed no pathological lesions with a significant improvement in the intestinal histomorpho-measures (villus height and width, villus surface area, lamina propria thickness, and tunica muscularis thickness) by NBA diets in a dose-dependent manner. In the fish intestine, the B. amyloliquefaciens count was increased in the NBA groups (NBA4 group followed by NBA2 group) with no discernible difference in the total bacterial count. Fish resistance to the A. hydrophila challenge was increased by increasing the survival % in the NBA4 group (91.70 %) followed by the NBA2 group (83.30 %) compared to the control group (70.80 %). Overall, dietary NBA (especially 104 CFU/kg diet) could be a promising feed supplement in the Nile tilapia diets for improving their growth, health, and resistance to bacterial challenges.

Protective effect of betaine supplementation in low-met diet against Aeromonas hydrophila-induced intestinal injury in grass carp (Ctenopharyngodon idella)

This study evaluated the effect of supplemental betaine in low-methionine (Met) diet concerning the regulatory role of bacteria-induced intestinal injury in fish. 540 grass carp (Ctenopharyngodon Idella) (210 ± 0.68 g) were selected and randomly divided into 6 groups, which contained a reference group fed with the diet supplemented with DL-Met (3.1 g kg−1 diet) and 5 groups fed on the diets added with increasing levels of betaine (0–6.4 g kg−1 diet) for 60 days. Then, a 14-day Aeromonas hydrophila challenge was conducted. Compared with BET0 group, results indicated that appropriate betaine supplementation (1) enhanced antioxidant enzymes activities (except glutathione S-transferase pi-1 (GSTP1) and copper zinc superoxide dismutase (CuZnSOD) and glutathione (GSH) contents, and NF-E2-related-factor 2 (Nrf2) protein nuclear translocation, while reduced reactive oxygen species (ROS), and representative oxidative damage markers; (2) up-regulated the transcription abundance of anti-apoptosis-related molecules while reduced DNA-ladder occurrence and the transcription levels of pro-apoptosis-related genes; (3) down-regulated the transcription of tight junction-related proteins (such as zonula occludens-1 (ZO-1) etc.) in fish intestines. Furthermore, correlation analysis revealed that feeding betaine ameliorating the oxidative damage, apoptosis and tight junction breakdown was possibly related to intestinal Nrf2, p38 mitogen-activated protein kinase (p38 MAPK) and c-Jun N-terminal kinases (JNK), and myosin light chain kinase (MLCK) signaling, respectively. According to the regression analysis for intestinal ROS abundance, claudin-b and caspase-2 transcription, the appropriate betaine supplementations were estimated to be 3.82, 3.98, and 3.62 g kg−1 diet, respectively. Notably, betaine has the potential to spare part Met and the efficacy of betaine relative to Met was 206.67 % based on intestinal ROS contents in grass carp (210–776 g).

Effects of mercury and magnetic fields on the activity of proteinases and glycosidases in the intestine of common carp Cyprinus carpio.

Aquatic ecosystems are increasingly affected by anthropogenic pollution, including heavy metals like mercury, which accumulate in organisms and cause harmful effects. At the same time, human activities such as industrial operations and the use of electric power lines also alter the magnetic background in natural water bodies. However, the interaction between mercury exposure and magnetic fields remains poorly understood. This study aimed to investigate the combined effects of mercury and magnetic fields on the digestive enzyme activity of common carp (Cyprinus carpio), focusing on the relevance of magnetic fields due to their increasing presence in industrialized environments. Two groups of fish were fed diets with low (0.02mg/kg) or high (0.27mg/kg) mercury content for 6months and exposed to extremely low-frequency magnetic fields or hypomagnetic conditions. Results showed significant differences in mercury accumulation between groups, with higher levels in carps fed with high-mercury content diets. These fish also exhibited increased body length and weight compared to those on a low-mercury diet. The amylolytic activity (total activity of enzymes hydrolyzing starch: α-amylase, glucoamylase, and maltase) and proteolytic activity (total activity of serine proteinases) in the fish intestine were assessed. Magnetic exposure had contrasting effects on enzyme activity, depending on mercury levels in the diet. Fish fed the low-mercury diet exhibited decreased amylolytic activity following magnetic field exposure, while fish on the high-mercury diet showed increased activity. Proteolytic activity followed a similar pattern, with opposite effects observed between the two dietary groups. These findings suggest that mercury accumulation alters the biological response to magnetic fields, possibly through compensatory biochemical mechanisms. Understanding the interactions between toxic substances and magnetic fields is critical for improving environmental risk assessments.