Fish Gut Research Articles

Coexistence mechanisms and individual trophic niche variation between functionally analogous non-native and native carp species

Understanding the mechanisms that promote coexistence between functionally analogous non-native and native species that share similar prey is important for predicting the ecological consequences of their competitive interactions. Theory predicts that species coexistence is facilitated by stabilizing mechanisms that enhance inter-specific trophic niche partitioning, and/ or the equalizing mechanisms that reduce differences in the average fitness. Inter-specific niche partitioning, influenced by the ecological opportunity in prey resources, also affects intra-specific niche partitioning and individual niche expansion. These theories were tested using the non-native mrigal carp Cirrhinus mrigala and its congener native mud carp C. molitorella that coexist across the Pearl River basin, Southern China, with their trophic interactions analysed using DNA metabarcoding on fish gut contents sampled across the basin in both the dry and wet seasons of 2019 and 2021. The results revealed that the inter-specific trophic niche overlap was lower than their intra-specific trophic niche overlap, suggesting their coexistence was supported by stabilizing mechanisms. The ecological opportunity in prey resources was driving inter-specific niche partitioning and this partitioning then positively influenced intra-specific niche partitioning and individual niche expansion, especially in mrigal carp that had larger body sizes and occupied higher trophic positions at constricted individual niches. Fish body size also affected inter-specific niche partitioning and the relationship between inter- and intra-specific niche partitioning, with positive effects on both in mrigal carp but negative effects on both in mud carp. The results thus provide a mechanistic explanation on how closely related non-native and native species coexist and highlight the importance of dietary plasticity in facilitating the invasion of non-native species.

TLR2/TLR5 Signaling and Gut Microbiota Mediate Soybean-Meal-Induced Enteritis and Declined Growth and Antioxidant Capabilities in Large Yellow Croaker (Larimichthys crocea)

Soybean meal, renowned for its high yield, cost efficiency, and protein richness, serves as a pivotal plant-based alternative to fish meal. However, high soybean meal inclusion in Larimichthys crocea diets is linked to enteritis and oxidative damage, with unknown mechanisms. Our study aims to elucidate the molecular basis of soybean-meal-induced enteritis and its impact on intestinal microbiota in L. crocea. To this end, four isonitrogenous and isolipidic diets with varying soybean meal levels (0% FM, 15% SBM15, 30% SBM30, and 45% SBM45) were administered to L. crocea for 8 weeks. The results indicated that the SBM30 and SBM45 treatments significantly hindered fish growth, digestive efficiency, and protein utilization. Furthermore, high soybean meal levels (SBM30 and SBM45) activated intestinal Toll-like receptors (TLR2A, TLR2B, TLR5, and TLR22), stimulating C-Rel and mTOR protein expression and elevating ERK phosphorylation. This led to increased pro-inflammatory cytokine production (IL-1β, IL-6, and TNF-α) and decreased anti-inflammatory cytokine expression (IL-4/13A, IL-4/13B, and TGF-β), suggesting a potential signaling pathway for soybean-meal-induced enteritis. Furthermore, enteritis induced by high soybean meal levels led to oxidative damage, evident from increased MDA levels and decreased antioxidant enzyme activities (SOD and CAT). The SBM30 and SBM45 treatments increased Firmicutes and Bacteroidetes abundance in fish gut microbiota, while Proteobacteria abundance decreased. This microbiota shift may enhance soybean meal nutrient utilization, yet high soybean meal concentrations still impair growth. A soybean-meal-rich diet promotes harmful bacteria like Rhodococcus and depletes probiotics like Ralstonia, increasing disease risks. L. crocea has limited tolerance for soybean meal, necessitating advanced processing to mitigate anti-nutritional factors. Ultimately, exploring alternative protein sources beyond soybean meal for fish meal replacement is optimal for L. crocea.

Fish guts possess higher priority in assessing ecological risk of microplastics in both fish bodies and aquatic environments

Microplastics (MPs, ＜5mm in size) have rapidly spread across aquatic ecosystems, which urgently needs systematic assessment for their ecological risk. Fish species have frequently been selected as indicator organisms in evaluating MPs contaminants. However, it has been questioned that which organs of fishes should be examined due to tissue-specific results. In this study, we investigated the accumulation and depuration process of MPs in the main organs of zebrafish under different MPs concentrations as well as the presence and absence of food resources. Our results recorded consistently higher MPs accumulation in fish guts among different MPs concentrations, implying fish guts as stable organs representing organisms’ MPs contaminants. Meanwhile, MPs accumulated in fish guts increased significantly with increasing exposure concentrations, highlighting fish guts as sensitive organs in reflecting MPs contamination in aquatic environments. In addition, MPs accumulated in fish guts under non-feeding conditions followed a logistic “S” curve while fluctuated under feeding conditions, suggesting increased ecological MPs risk with the absence of food resources. The depuration rate in fish guts was significantly higher in the feeding group than in the non-feeding group, implying better expelling ability of MPs with the presence of food resources. Our study proposes fish guts as the optimal indicator organs in assessing the ecological risk of MPs contaminants in both fish bodies and aquatic environments, and highlights the importance of sustaining sufficient food resources in aquatic environments to reduce the MPs triggered adverse effects on fish species.

Microbiome and network analysis reveal potential mechanisms underlying Carassius auratus diseases: The interactions between critical environmental and microbial factors

Despite the rapid development of research on aquatic environment microbiota, limited attention has been paid to exploring the complex interactions between microbial communities and aquatic environments. Particularly, the mechanisms underlying fish diseases based on such dynamic interactions remain unknown. This study aimed to address the gap by conducting microbiome and co-occurrence network analyses on the typical freshwater aquaculture systems. High-throughput 16S rRNA gene sequencing results revealed significant differences in the microbiota between the disease and healthy groups. Notably, disease mortality varied consistently with the gradient of relative abundance of Proteobacteria (intestine, R2 = 0.46, p < 0.05) and Cyanobacteria (gill, R2 = 0.67, p < 0.01), indicating their potential use as diagnostic criteria. Furthermore, the elevated hepatosomatic index, NO3-N, COD and TC (sediment) were directly correlated with diseases (r > 0.54, p < 0.01). Mean concentrations of NO3-N, COD and TC were elevated by 78.87%, 25.63% and 44.2%, respectively, in ponds where diseases occurred. Quantitative analysis (qPCR) revealed that Aeromonas sobria infected hosts through a potential pathway of “sediment (4.4 × 105 copy number/g)-water (1.1 × 103 copy number/mL)-intestine (1.2 × 106 copy number/g)”. Similarly, the potential route for Aeromonas veronii was sediment (4.9 × 106 copy number/g) to gill (5.1 × 105 copy number/g). Additionally, the complexity of microbial networks in the intestine, water, and sediment was significantly lower in the disease group, although no similar phenomenon was observed in the gill microbial network. In summary, these findings reveal that elevated concentrations of crucial environmental factors disrupt the linkages within microbiota, fostering the growth of opportunistic bacteria capable of colonizing fish gut or gills. This offers new insights into potential mechanisms by which environmental factors cause disease in fish.

Dietary vitamin E (α-tocopherol acetate) modulates growth, digestive enzymes, histopathology, and vulnerability of Nile tilapia, Oreochromis niloticus to Aeromonas hydrophila infection

Vitamin E is a fat-soluble vitamin that plays a vital function in several biological processes, and fish cannot synthesize it to meet their requirement. So, 56-day research was conducted to examine the influence of vitamin E (vit-E) (α-tocopherol acetate) on the Nile tilapia's growth, digestive enzymes, hematology, histology, and susceptibility to Aeromonas hydrophila. A total of 450 mono-sex Acclimated Nile tilapia (Oreochromis niloticus) were haphazardly dispersed into 30 aquaria, each with a capacity of 100 liters (15 fish/aquarium) to exemplify five groups with six replicates. A control diet (30 % protein) was enriched with 0.0 (E0), 150 (E150), 300 (E300), 600 (E600), and 1200 (E1200) mg/kg feed. Fish (13.5 ± 0.12 g) were given the trial diets until obvious satiation thrice daily for 56 days. At the end of the feeding trial, growth performance, digestive enzymes, hematology, and histology for the mid-intestine were examined. Subsequently, twenty fish from each treatment were challenged to contagion with Aeromonas hydrophila bacteria, and fish mortality was recorded for a further 14 days. At the end of the bacterial challenge, histology for the mid-intestine, liver, and spleen tissues was examined. Growth performance, feed utilization, and digestive enzyme secretion (proteases, lipase, and α-amylase) were substantially (P < 0.5) improved with raising vit-E levels in fish feeds up to E1200. Increasing the vit-E doses improved fish gut histomorphology by increasing the count and size of intestinal folds bordered by well-arranged enterocytes. The body composition was not influenced by dietary vitamin E, except lipid content, which increased substantially as vitamin E levels increased. Fish fed with vita-E enriched diets had higher resistance to A. hydrophila infection; however, the control group exhibited the greatest fish mortality rate (80 %), while the lowest rate was observed at E1200 (30 %). Hepatic and spleen tissues in the control group (E0) showed severe congestion and degeneration, whereas vit-E-treated fish groups progressively recovered normal histomorphology depending on the vit-E doses. Finally, this research recommends feeding Nile tilapia on vit-E, particularly 1200 mg/kg feed, to enhance its performance, welfare status, and resistance to A. hydrophila contagion.

Associations Between Gut Microbiota Diversity and a Host Fitness Proxy in a Naturalistic Experiment Using Threespine Stickleback Fish.

The vertebrate gut microbiota is a critical determinant of organismal function, yet whether and how gut microbial communities affect host fitness under natural conditions remains largely unclear. We characterised associations between a fitness proxy-individual growth rate-and bacterial gut microbiota diversity and composition in threespine stickleback fish introduced to large semi-natural ponds. We detected a 63% higher richness of bacterial taxa (α-diversity) in the guts of high-fitness fish compared to low-fitness fish, which might be driven by stronger bacterial dispersal among high-fitness fish according to the fit of a neutral community model. Further, microbial communities of high-fitness fish were more similar to one another (i.e., exhibited lower β-diversity) than those of low-fitness fish. The lower β-diversity found to be associated with higher host fitness is consistent with the Anna Karenina principle-that there are fewer ways to have a functional microbiota than a dysfunctional microbiota. Our study links differences in α- and β-diversity to a fitness-related trait in a vertebrate species reared under naturalistic conditions and our findings provide a basis for functional tests of the fitness consequences of host-microbiota interactions.

Comparative microbial community occurrence pattern, growth attributes, and digestive enzyme indices of Puntius gonionotus (Bleeker, 1850), Pangasianodon hypophthalmus (Sauvage, 1878) and Heteropneustus fossilis (Bloch, 1794) under freshwater biofloc based polyculture system

BackgroundThe biofloc system (BFS) provides a sustainable aquaculture system through its efficient in situ water quality maintenance by the microbial biomass, besides continuous availability of these protein-rich microbes as feed to enhance growth and immunity of the reared organism. This study explores the gill architecture, growth performance, digestive enzyme activity, intestinal microbial composition, and histology of three freshwater fish species, Puntius gonionotus, Pangasianodon hypophthalmus, and Heteropneustus fossilis reared in biofloc based polyculture system.ResultsThe three species in T2 showed significantly higher WG and SGR, followed by T1 and T3. The wet mount of gill architecture showed smaller inter-filament gaps in gill arches of silver barb followed by stinging catfish and stripped catfish, but showed no correlation with the weight gain. However, silver barb being an omnivore and filter-feeder, accumulated a more diverse microbial community, both in T1 and BFS (T2 and T3), while the bottom feeder H. fossilis exhibited unique gut bacterial adaptability. The presence of floc in T2 and T3 enhanced bacterial abundance in water and fish gut, but their microbial diversities significantly reduced compared to T1 receiving only feed. Next-generation sequencing revealed that the Pseudomonas dominated in gut of P. gonionotus and P. hypophthalmus in T1, Enterobacterales and Fusobacterium prevailed in those of T2 and T3, respectively. In contrast, gut of H. fossilis had the highest proportion of Clostridium in T1, while Rhizobiaceae dominated in T3. Similarly in floc samples, Enterococcus dominated in T1 while Micrococcales and Rhizobiaceae dominated in T2 and T3, respectively. A positive correlation of enterobacteria, with the digestive enzyme activities and growth patterns was observed in all treatments.ConclusionThe present study revealed feeding behaviour to play crucial role in distinguishing the gut microbial composition patterns in fishes reared in Biofloc System. Further it revealed the requirement of supplementary feed along with floc in these three species for higher growth in the biofloc system.

Mandarin Fish Ranavirus (MRV) Infection Induced Inflammation and Histologic Lesions in the Gut of Mandarin Fish.

Mandarin fish ranavirus (MRV) is widely spread in China and causes huge economic losses to the mandarin fish (Siniperca chuatsi) aquaculture. However, the pathogenesis of MRV is still unclear. In the present study, mandarin fish were artificially infected with MRV, and then different gut compartments from diseased fish were subjected to histologic analysis by H&E staining, quantification of proinflammatory genes and MRV copies by qPCR. MRV-MCP protein expression was assessed using indirect fluorescence assay (IFA) and immunohistochemistry. Proliferation of IgM+ B cells was evaluated by indirect fluorescence assay (IFA). Then, we found that MRV infection caused serious histologic lesions along with inflammatory cell infiltration, especially in the foregut. A significant accumulation of IgM+ B cells was detected in the foregut (~6.5-fold) and hindgut (~3.3-fold), respectively. The expression of inflammation-related genes such as IL-1β, IL-6, IL-8,TNF-α, CSF1r and NCF1 was significantly upregulated in the foregut, varying from ~2.8-fold to ~11.9-fold. In addition, MRV exhibited foregut tropism, according to the investigation of viral loads and MCP protein expression. Overall, our findings indicated that MRV-induced hyperinflammation in the gut eventually led to enteritis. This study provided new insights into uncovering the pathogenesis of MRV infection.

Comparative Analysis of Intestinal Morphology and Gut Microbiota of Spinibarbus sinensis Under Different Aquaculture Systems

Fish gut health is influenced by various factors, with the environment being a significant one. S. sinensis is a key aquaculture species in China, yet research on the impact of different aquaculture systems on its intestinal health remains limited. This study aims to explore the changes in intestinal morphology and gut microbiota of S. sinensis under two aquaculture systems. The juveniles of S. sinensis were divided into two groups and cultured in traditional ponds (CT) and an in-pond tank culture system (JY), with equal amounts of feed provided daily over a 72-day experimental period. The results showed no significant differences in growth performance metrics, including the specific growth rate, weight gain rate, hepatosomatic index, and viscerosomatic index between the two groups. In terms of intestinal morphology, the JY group villus width was significantly wider than the CT group, and the number of goblet cells in the CT group was significantly higher than that of the JY group (p &lt; 0.05), which suggested that the fish in the JY group may have better intestinal nutrient absorption capacity, while the water quality in the CT group may be worse. The 16S rRNA gene sequencing analysis of the gut microbiota showed that the JY group had a significantly higher Shannon index compared to the CT group (p &lt; 0.05), indicating greater species richness and evenness. Principal Coordinates Analysis (PCoA) revealed a distinct clustering of gut microbiota between the two groups. At the phylum level, the relative abundance of Fusobacteriota was significantly higher in the CT group, whereas Bacteroidota and Proteobacteria were significantly higher in the JY group (p &lt; 0.05). Furthermore, KEGG pathway predictions indicated differences in the potential metabolic capabilities of the gut microbiota between the two groups (p &lt; 0.05). Overall, this study is the first to conduct a comparative analysis of the growth performance, intestinal tissue morphology, and gut microbiota of S. sinensis under two different aquaculture systems, which has valuable implications for the further optimization of aquaculture practices.

The need for high-resolution gut microbiome characterization to design efficient strategies for sustainable aquaculture production

Microbiome-directed dietary interventions such as microbiota-directed fibers (MDFs) have a proven track record in eliciting responses in beneficial gut microbes and are increasingly being promoted as an effective strategy to improve animal production systems. Here we used initial metataxonomic data on fish gut microbiomes as well as a wealth of a priori mammalian microbiome knowledge on α-mannooligosaccharides (MOS) and β-mannan-derived MDFs to study effects of such feed supplements in Atlantic salmon (Salmo salar) and their impact on its gut microbiome composition and functionalities. Our multi-omic analysis revealed that the investigated MDFs (two α-mannans and an acetylated β-galactoglucomannan), at a dose of 0.2% in the diet, had negligible effects on both host gene expression, and gut microbiome structure and function under the studied conditions. While a subsequent trial using a higher (4%) dietary inclusion of β-mannan significantly shifted the gut microbiome composition, there were still no biologically relevant effects on salmon metabolism and physiology. Only a single Burkholderia-Caballeronia-Paraburkholderia (BCP) population demonstrated consistent and significant abundance shifts across both feeding trials, although with no evidence of β-mannan utilization capabilities or changes in gene transcripts for producing metabolites beneficial to the host. In light of these findings, we revisited our omics data to predict and outline previously unreported and potentially beneficial endogenous lactic acid bacteria that should be targeted with future, conceivably more suitable, MDF strategies for salmon.

Microcystin exposure alters gut microbiota composition in fish: An in-Situ analysis of post-bloom effects in Hulun Lake, China

Cyanobacterial blooms are one of the most common stressors aquatic plants and animals encounter in freshwater ecosystems such as rivers and lakes. Following such outbreaks, some cyanobacteria release toxins, notably microcystins, which are highly toxic. Although numerous studies have explored the effects of microcystins on fish, their in-situ effects on the fish gut microbiome remain unexamined. Our objectives were to examine the fish gut microbiome before (Ju) and after (Au) cyanobacterial blooms and to monitor water quality. We collected Ju and Au fish gut and water samples from Hulun Lake. Using 16S rRNA full-length sequencing, we analyzed the composition, structure, and function of the fish gut microbiome. Results revealed significant disparities in microcystin concentrations between the Ju and Au water samples. In addition, the microcystin concentration in the carp gut was significantly higher than that in its muscle after the cyanobacterial bloom outbreak. Notably, the Au group demonstrated an increase in the microcystin level in water and a marked reduction in fish gut microbiota diversity compared with the Ju group. The cyanobacterial bloom decreased gut microbiome diversity in fish, with the Au group exhibiting a significantly reduced abundance of bacteria related to gut stability and microcystin degradation compared to the Ju group. Furthermore, we observed an upregulation of disease-associated bacterial metabolic functions in the Au group. In conclusion, these findings suggest that microcystins influence the composition and function of fish gut microbiota, improving our understanding of the interaction between fish gut microbiome and their environment. This study offers new perspectives on the adaptive mechanisms of aquatic organisms to cyanobacterial blooms.

Xylanase enhances gut microbiota-derived butyrate to exert immune-protective effects in a histone deacetylase-dependent manner

BackgroundCommensal bacteria in the intestine release enzymes to degrade and ferment dietary components, producing beneficial metabolites. However, the regulatory effects of microbial-derived enzymes on the intestinal microbiota composition and the influence on host health remain elusive. Xylanase can degrade xylan into oligosaccharides, showing wide application in feed industry.ResultsTo validate the immune-protective effects of xylanase, Nile tilapia was used as the model and fed with xylanase. The results showed that dietary xylanase improved the survival rate of Nile tilapia when they were challenged with Aeromonas hydrophila. The transcriptome analysis showed significant enrichment of genes related to interleukin-17d (il-17d) signaling pathway in the xylanase treatment group. High-throughput sequencing revealed that dietary xylanase altered the composition of the intestinal microbiota and directly promoted the proliferation of Allobaculum stercoricanis which could produce butyrate in vitro. Consequently, dietary xylanase supplementation increased the butyrate level in fish gut. Further experiment verified that butyrate supplementation enhanced the expression of il-17d and regenerating islet-derived 3 gamma (reg3g) in the gut. The knockdown experiment of il-17d confirmed that il-17d is necessary for butyrate to protect Nile tilapia from pathogen resistance. Flow cytometry analysis indicated that butyrate increased the abundance of IL-17D+ intestinal epithelial cells in fish. Mechanistically, butyrate functions as an HDAC3 inhibitor, enhancing il-17d expression and playing a crucial role in pathogen resistance.ConclusionDietary xylanase significantly altered the composition of intestinal microbiota and increased the content of butyrate in the intestine. Butyrate activated the transcription of il-17d in intestinal epithelial cells by inhibiting histone deacetylase 3, thereby protecting the Nile tilapia from pathogen infection. This study elucidated how microbial-derived xylanase regulates host immune function, providing a theoretical basis for the development and application of functional enzymes.7BVRPuQYn3eQdwFeU5j8vPVideo

Gut microbiome as biomarker for triclosan toxicity in Labeo rohita: bioconcentration, immunotoxicity and metagenomic profiling.

Triclosan (TCS) is a lipophilic, broad spectrum antimicrobial agent commonly used in personal care products with a projected continuous escalation in aquatic environments in the post COVID 19 era. There is rich documentation in the literature on the alteration of physiological responses in fish due to TCS exposure; however, studies on gut associated bacteria of fish are still scarce. This is the first attempt to determine changes in bacterial community structure due to exposure of TCS on Labeo rohita, a commercially essential freshwater species, using 16S V3-V4 region ribosomal RNA (rRNA) next-generation sequencing (NGS). Chronic exposure of TCS at environmentally realistic concentrations viz. 1/5th (T1: 0.129 mg/L) and 1/10th (T2: 0.065 mg/L) of LC50 for 28 days resulted in the dose dependent bioconcentration of TCS in the fish gut. Prolonged exposure to TCS leads to disruption of gut bacteria evidenced by down regulation of the host immune system. Additionally, high-throughput sequencing analysis showed alternation in the abundance and diversity of microbial communities in the gut, signifying Proteobacteria and Verrucomicrobia as dominant phyla. Significant changes were also observed in the relative abundance of Chloroflexi and Gammatimonadetes phyla in TCS exposed groups. The study revealed that gut microbiome can be used as a biomarker in assessing the degree of TCS toxicity in commercially important fish species.

Effects of poultry by-product meal and complete replacement of fish oil with alternative oils on growth performance and gut health of rainbow trout (Oncorhynchus mykiss): a FEEDNETICS™ validation study

BackgroundAquaculture, traditionally a form of biotechnology, has evolved to integrate innovative biotechnological applications, such as advanced feed formulations, aimed at improving the growth performance and health of farmed fish species. In the present study, the effects of feeding rainbow trout with novel feed formulations were investigated. Fish growth, gut and liver morphology, the concentration of fatty acids in the fillet, and volatile fatty acids in the gut were assessed. The study also validated scenarios from in vivo experiments using a nutrient-based model called FEEDNETICS™. This globally used model serves as a tool for data interpretation and decision support in the context of precision fish farming.MethodsAlternative protein and oil sources, including poultry by-product meal (PBM) and natural algae oil, were explored as sustainable replacements for fishmeal (FM) and fish oil (FO). A 90-day feeding trial was conducted using rainbow trout, comparing two isoproteic, isolipidic and isoenergetic diets. The control diet contained 15% FM, 5% PBM, and 8% FO, while the test diet replaced FM with 15% PBM and 5% feather meal hydrolysate (FMH), and fully substituted FO with VeraMaris® natural algae oil and rapeseed oil.ResultsPBM successfully replaced FM protein without negatively affecting feed intake, growth performance or feed utilization in trout. The combination of PBM and natural algae oil was well tolerated by the trout and showed no negative effects on gut health. A detailed analysis of fatty acids in the fillet revealed that PUFAs of the n3 and n6 series were significantly higher in the PBM group than in the FM group. Values of fatty acid-related health indexes, including atherogenicity index, and thrombogenicity index, confirmed the high nutritional value of trout filet, thus representing a healthy product for human. In addition, the predictions using the FEEDNETICS™ indicated that the tested novel alternative formulations are economically viable. The validation of the model for fish growth resulted in a Mean Absolute Percentage Error (MAPE) of 8%.ConclusionsThe FEEDNETICS™ application enhances our ability to optimize feeding strategies and improve production efficiency in the aquaculture industry. VeraMaris® algae oil and PBM could serve as viable and sustainable raw materials for fish feed, promoting environmentally friendly aquaculture practices.

Making in vitro conditions more reflective of in vivo conditions for research on the teleost gastrointestinal tract.

To date, the majority of in vitro or ex vivo fish gastrointestinal research has been conducted under unrealistic conditions. In a living fish, ionic conditions, as well as levels of ammonia, pH, HCO3- and PCO2differ considerably between the different regions of the gastrointestinal tract. These factors also differ from those of the saline often used in gut research. Furthermore, the oxygen gradient from the serosa to the gut lumen is rarely considered: in contrast to the serosa, the lumen is a hypoxic/anoxic environment. In addition, the gut microbiome plays a significant role in gut physiology, increasing the complexity of the in vivo gut, but replicating the microbial community for in vitro studies is exceptionally difficult. However, there are ways in which we can begin to overcome these challenges. Firstly, the luminal chemistry and PO2in each gut compartment must be carefully considered. Secondly, although microbiological culture techniques are improving, we must learn how to maintain the microbiome diversity seen in vivo. Finally, for ex vivo studies, developing mucosal (luminal) solutions that more closely mimic the in vivo conditions will better replicate physiological processes. Within the field of mammalian gut physiology, great advances in 'gut-on-chip' devices are providing the tools to better replicate in vivo conditions; adopting and adapting this technology may assist in fish gut research initiatives. This Commentary aims to make fish gut physiologists aware of the various issues in replicating the in vivo conditions and identifies solutions as well as those areas that require further improvement.

Meta-analysis of the effects of microplastic on fish: Insights into growth, survival, reproduction, oxidative stress, and gut microbiota diversity

Aquatic ecosystems are primary repositories for microplastics (MPs), which pose significant risks to aquatic organisms. This study addresses the gap in understanding the effects of MPs pollution by analyzing 3,757 biological endpoints from 85 laboratory studies. Overall, our results indicate that MPs exposure significantly inhibits fish growth, survival, and reproductive ability, and increases oxidative damage, specifically, MPs exposure leads to elevated levels of malondialdehyde. However, MPs do not have a significant impact on the diversity of fish gut microbiota. Subgroup and correlation analyses indicate that the extent of various toxic effects is influenced by multiple factors, including MPs’ type, exposure pathway, size, concentration, as well as the aquatic environment or life stage of the fish. In addition, the regression analysis revealed a relationship between the magnitude of toxic effects and the size, concentration, or duration of MPs exposure. This study provides useful information for understanding the potential impacts of MPs on aquatic organisms and offers new insights for the protection and management of aquatic ecosystems.

Identification of Protease Producing Bacteria From Fish Gut.

Identification of Protease Producing Bacteria From Fish Gut.

Mangrove forest ecological function is influenced by the environmental settings and the benthic fauna composition

Benthic communities perform many important roles within mangrove ecosystems and are responsible for facilitating many of the functions attributed to mangrove forests. For instance, they are instrumental in mediating mangrove system productivity, and provide crucial food for juvenile nekton. Despite their importance, very few studies have investigated the benthic community of mangrove forests, and among those the results are inconsistent. This variability manifests in strong location effects, with low organism density and species richness in Indo-Pacific mangroves, compared to West Atlantic sites. These regional difference are confounded by differences in within-region environmental settings (e.g. rainfall, tidal range, spatial location along the coastal mosaic), and this complicates the development of a clear understanding of underlying consistencies. To assess the influence of contrasting environmental influences on the benthic community of mangrove forests we studied the benthic community of Rhizophora stylosa forests at two coastal estuaries and along the shores of two islands within a 75 km radius. The results showed that the community composition differed among settings, with several taxa only occurring at one of the two forests type. Furthermore, Peracarida, a common prey found in the gut of juvenile fish, was only found through the island forests, but never observed within the estuarine forests. This indicates that environmental setting can play a key role in determining the nature of mangrove benthic assemblages and their potential ecological roles. Consequently, caution is required when attributing the ecological roles of mangrove forests without accounting for changes in settings. Additionally, we only investigated a single mangrove species within the same climatic region, meaning that even greater variability is likely when the full range of mangrove types, conditions and areas are assessed. Understanding this variation is important because it implies that mangrove forest restoration projects are unlikely to achieve their desired outcomes unless setting-specific conditions are understood and taken into account.

Plastics at an Offshore Fish Farm on the South Coast of Madeira Island (Portugal): A Preliminary Evaluation of Their Origin, Type, and Impact on Farmed Fish

Plastic pollution is a global problem affecting all ecosystems, and it represents most of the marine litter. Offshore aquaculture is a sector particularly vulnerable to this issue. To investigate this concern, the present study employed videography to monitor macroplastics at an offshore fish farm on Madeira Island (Portugal) and analysis of fish gut content to evaluate macroplastic ingestion by farmed sea bream Sparus aurata. Our analysis revealed that the majority of identified plastic debris originated from domestic use (66.66%) and fisheries/aquaculture activities (24.99%). While the number of dead fish suitable for sampling was limited (1.05% of the total mortality), macroplastic debris ingestion was identified in 5.15% of the total mortalities and reported for the first time in species in offshore farming conditions. Fish ingested fragmented plastic sheets, with the amount positively correlated with fish weight (r = 0.621, p = 0.031, n = 12). Notably, the stretched length of these fragments exceeded 50% of the standard length of most fish. Inconsistencies were observed in the number of samples collected per cage and per week. To ensure robust results, these discrepancies should be rectified in future studies. Additionally, extending the sampling period to encompass all seasons would be beneficial for a more comprehensive understanding of seasonal variations in plastic occurrence.

Evaluation of the potential probiotic Bacillus subtilis isolated from darkbarbel catfish (Pelteobagrus fulvidraco) on growth performance, serum immunity, and disease resistance of Aeromonas hydrophila.

This study aimed to identify potential probiotic strains of Bacillus subtilis from healthy fish gut microbiota for application in aquaculture. The effects of dietary B. subtilis administration on growth performance, serum enzyme activity, immune gene expression, and disease resistance in darkbarbel catfish (Pelteobagrus fulvidraco) were investigated. The isolate, identified through gene sequencing and biochemical tests, demonstrated resilience to pH 3.0% and 6.0% bile, and exhibited extracellular protease, cellulose, lipase, and amylase production. Darkbarbel catfish were fed diets with varying B. subtilis concentrations (0 CFU/kg [T0], 107 CFU/kg [T1], 108 CFU/kg [T2], and 109 CFU/kg [T3]). After 8 weeks, significant increases (p < 0.05) were observed in final body weight, weight gain rate, specific growth rate, serum lysozyme, serum superoxide dismutase, alkaline phosphatase, and total antioxidant capacity, whereas malondialdehyde levels significantly decreased. Feeding darkbarbel catfish with B. subtilis diets increased immunoglobulin M (IgM) and C3 gene expression (p < 0.05), indicating a positive impact on the fish's immune system. The strain upregulated interleukin 10 (IL-10) and transforming growth factor-β (TGF-β) expression and downregulated TNF-α and IL-1β, suggesting potential anti-inflammatory effects. Following a 7-day challenge with Aeromonas hydrophila, fish fed with B. subtilis exhibited lower mortality, with higher survival rates in the T2 and T3 groups. In conclusion, supplementing darkbarbel catfish diets with B. subtilis effectively enhances growth performance, immune response, and disease resistance.