Carnivorous Species Research Articles (Page 1)

Aquaculture sector growth is challenged by feed constraints, particularly the erratic availability and cost of fishmeal and oil from wild forage fish. Limited attention is given to the risks that forage fish shortfalls pose to aquaculture feed supplies. Here we develop a shortfall impact model to investigate the effects of varying forage fish supply scenarios on global fed aquaculture. Results suggest fisheries management interventions and persistent climate impact could reduce forage fish catches by 4.5% to 19.4%, resulting in an 8% to 35.2% decline in fed aquaculture production. Countries cultivating carnivorous species and leading aquaculture-producing nations are most affected. To sustain production, 1.8 million tonnes of alternative ingredients annually will be required, highlighting the urgent need for cost-effective alternatives to ensure resilience.

Evidence for reducing fitness and competition of the native fish with invasive fish species in the south Caspian Sea.

This study analyzed microplastics (MPs; target size: 0.1-5mm) in freshwater fish and aquatic plants in an urban lake in Kumamoto, Japan. MPs were detected in 82% of the collected sample of herbivorous fish species, Nile tilapia (Oreochromis niloticus) and Redbelly tilapia (Tilapia zillii) at mean level of 10 ± 13 items ind-1, which was more than 10 times higher than the levels found in two carnivorous fish species, largemouth bass (Micropterus salmoides) and snakehead (Channa argus). Fish samples near the outlets of stormwater runoff and a wastewater treatment plant showed higher abundances of MPs than fish collected from other locations in the lake. Polyethylene (PE), polypropylene (PP), and polyethylene terephthalate (PET) were dominant polymers in fish, accounting for 83%. These three polymers were also commonly detected in three species of aquatic plants, which retained MPs at 4.6-35itemsg-1 dry weight. A comparison of the characteristics of the MPs detected in the herbivorous fish and aquatic plant samples collected at the same station showed similar profiles in terms of polymer types, shape, and colors. This indicates that herbivorous fish are exposed to MPs adsorbed onto the surface of aquatic plants through their feeding activity. Our findings highlighted that aquatic plants act as a mediator to increase the bioavailability of MPs in freshwater fish by trapping MPs on the plant surface.

Fish assemblages are vital for the functioning of Mediterranean coastal ecosystems, yet they have long been overexploited by recreational and professional fishing. In response to this overexploitation, No-take Zones (NTZs) have been applied, resulting in significant conservation benefits. This study, conducted by citizen scientists and members of the scientific community in the north-western (NW) Mediterranean Sea, investigated spatial trends in fish assemblages targeted by small scale and recreational fisheries using the Fish Assemblage Survey Technique (FAST). A total of 1356 fifteen-minute replicate counts, corresponding to 452 hours in the water over a six-year period (2018 – 2023) were analyzed. Results indicated that the ecological status of fish assemblages were spatially dependent, where poor fish assemblage health was observed at dive sites situated in the Lérins Islands, highlighting an area of conservation priority. NTZs were associated with a higher presence of small (p < 0.001) and large (p <0.001) size classes of Serranidae fishes. They were also associated with a higher presence of large, threatened carnivorous species: Dentex dentex (p < 0.001), Epinephelus marginatus (p < 0.001), and Sciaena umbra (p < 0.001). Results from this study suggested that data collected by citizen scientists using FAST was robust enough to meet the same conclusions as researchers. We conclude on the positive application of citizen science programs to assess the ecological status of fish assemblages; fill the need for simple, effective monitoring in Marine Protected Areas (MPAs) and understudied areas; and inform conservation policies focused on threatened habitats and associated marine biodiversity in the French region Provence-Alpes-Côte d’Azur (PACA).

Chrotopterus auritus is a rare carnivorous species in the Neotropical region. The helminth fauna of this bat is poorly known, with only 1 published record in Peru. In Mexico, C. auritus is classified as endangered, mainly due to deforestation. The study of helminths in wildlife is relevant, as they can influence behavior, population dynamics, and evolution of their hosts, regulating populations and contributing to the maintenance of biodiversity. As a part of a DNA barcoding survey of bats in Mexico, a specimen of C. auritus was examined for helminths. Only three adult female nematodes were recovered from the intestine of this bat. Nematodes were morphologically studied using light microscopy and scanning electron microscopy. In addition, the 28S ribosomal RNA (28S) gene and the cytochrome c oxidase subunit 1 (COI) gene of 1 specimen were amplified and sequenced. Nucleotide sequences obtained from our specimen were used for phylogenetic analyses. The morphology observed in 2 specimens (e. g. cephalic structures, esophagus, rows of spines, vulva, and tail) agreed with characteristics established for the genus Seuratum. Phylogenetic analyses of the superfamily Seuratoidea grouped our 28S and COI sequences of Seuratum sp. with Paraquimperia sp., a species of the family Quimperiidae. The morphology observed in the female specimens differ from those reported for Seuratum cancellatum, the only species reported from Neotropical bats. This suggests that the specimens found in Yucatan represent a distinct, potentially new species. However, additional specimens, particularly males, are needed to confirm this hypothesis. This study provides the first helminthological record in C. auritus from Mexico, as well as the first 28S and COI sequences for members of the family Seuratidea.

The early developmental transition from endogenous to exogenous feeding is a critical period in carnivorous fish larvae, often associated with high mortality rates in aquaculture. Although trypsin, a key protease in protein digestion, is hypothesized to play a pivotal role in initiating exogenous feeding, the expression dynamics and functional contributions of trypsin and isoforms during early development remain poorly characterized in carnivorous species. This study explores the critical role of trypsin in the early feeding process of carnivorous fish, using mandarin fish (Siniperca chuatsi) as a model, which is a commercially valuable species that faces significant challenges during this phase due to its strict dependence on live prey and underdeveloped digestive system. Phylogenetic analysis indicates that, compared to herbivorous and omnivorous fish, carnivorous fish have evolved a greater number of trypsins, with a distinct branch specifically dedicated to try. RNA-seq data revealed the expression profiles of 13 trypsins during the early developmental stages of the mandarin fish. Most trypsins began to be expressed in large quantities with the appearance of the pancreas, reaching a peak prior to feeding. In situ hybridization revealed the spatiotemporal expression pattern of trypsins, starting from the pancreas in early development and later extending to the intestines. Furthermore, inhibition of trypsins activity successfully suppressed early oral feeding in mandarin fish, which was achieved by increasing the expression of cholecystokinin 2 (CCK2) and proopiomelanocortin (POMC) to suppress appetite. These findings enhance our understanding of the adaptive relationship between the ontogeny of the digestive enzyme system and feeding behavior in carnivorous fish. This research may help alleviate bottleneck issues in aquaculture production by improving the survival rate and growth performance of carnivorous fish during critical early life stages.

Simple SummaryOlfaction plays a crucial role in regulating feeding behaviors and ecological adaptation in fish. However, the molecular mechanisms underlying olfactory adaptation in fish species with distinct feeding habits remain largely unexplored. In this study, we conducted comparative transcriptomic analyses of olfactory rosettes from four Xenocyprididae species representing herbivorous and carnivorous diets. We identified and functionally annotated unigenes, screened olfaction-related genes, and analyzed the expression patterns of single-copy orthologs. Furthermore, positive selection analysis revealed molecular evolutionary signals associated with olfactory function. Our findings demonstrate distinct expression trends and evolutionary patterns between herbivorous and carnivorous species, providing new insights into the functional specialization and adaptive evolution of the olfactory system in freshwater fish.Olfaction plays a crucial role in fish feeding behaviors and ecological adaptation. However, systematic studies on its transcriptional regulation and molecular evolutionary mechanisms in herbivorous and carnivorous fishes remain scarce. In this study, we analyzed four Xenocyprididae species: two herbivorous (Ctenopharyngodon idella and Megalobrama amblycephala) and two carnivorous (Elopichthys bambusa and Culter alburnus), using olfactory rosette transcriptome sequencing and cross-species comparisons. The number of unigenes per species ranged from 40,229 to 42,405, with BUSCO completeness exceeding 89.2%. Functional annotation was performed using six major databases. Olfactory-related candidate genes were identified based on Pfam domains (7tm_4) and KEGG pathways (ko04740), revealing 8–19 olfactory receptor genes per species. These candidate genes were predominantly enriched in the olfactory transduction and neuroactive ligand–receptor interaction pathways. A total of 3681 single-copy orthologous genes were identified, and their expression profiles exhibited clear interspecific divergence without forming strict clustering by dietary type. High-threshold differentially expressed trend genes (|log2FC| ≥ 4) were enriched in pathways related to RNA processing, metabolite transport, and xenobiotic metabolism, suggesting that the olfactory system may participate in diverse adaptive responses. Ka/Ks analysis indicated that most homologous genes were under purifying selection, with only 0.87–2.07% showing positive selection. These positively selected genes were enriched in pathways related to immune response and neural regulation, implying potential roles in adaptive evolution associated with ecological behavior. Furthermore, the olfactory-related gene oard1 exhibited Ka/Ks > 1 in the E. bambusa vs. C. idella comparison. qRT-PCR validation confirmed the reliability of the RNA-Seq data. This work is the first to integrate two complementary indicators—expression trends and evolutionary rates—to systematically investigate the transcriptional regulation and molecular evolution of the olfactory system in Xenocyprididae species under the context of dietary differentiation, providing valuable reference data for understanding the perceptual basis of dietary adaptation in freshwater fish.

Habitat fragmentation and the disruption of connectivity caused by roads are major concerns for the conservation of large carnivores as apex predator. The central arid plains of Iran support a variety of carnivore species, which their populations have sharply decreased because of habitat destruction, deterioration, and fragmentation. This study was conducted in the three conservation areas (CAs) and surrounded landscapes in central plains of Iran, focusing on two large carnivores: the grey wolf and the Persian leopard. The objectives were to predict habitat suitability and identify the environmental variables influencing the distribution of these carnivores. Additionally, the study aimed to predict core habitats and corridors, as well as their integration with CAs. Furthermore, road densities and the number of road crossings relevant to the assessed carnivores were applied. An ensemble modeling approach for habitat suitability, which includes five different algorithms and factorial least cost analysis were applied to predict habitat suitability, core habitats and their connectivity. The results indicated that the most important variables for habitat suitability were distance to CAs, grassland density, and distance to water resources for both carnivores. Three core habitats were identified for the grey wolf, while two core habitats were identified for the Persian leopard. The coverage of predicted core habitats within CAs exceeded 90%. However, the high road density within the corridors for grey wolves (80 m/km²) and particularly for Persian leopards (152 m/km²) in our study area indicated that the habitat was fragmented by roads for the assessed carnivorous species. To enhance connectivity and reduce habitat fragmentation, it is recommended to facilitate the movement of carnivores within corridors by implementing warning signs and speed cameras in areas bisected by roads. Integrated management of core habitats and corridors for the assessed carnivores, encompassing both conservation and road management, should be prioritized by wildlife managers in the study area.Supplementary InformationThe online version contains supplementary material available at 10.1038/s41598-025-17644-4.

Quantitative assessment of microplastics in fish from the Gulf of Guinea, Ghana, using LDIR spectroscopy: Implications for marine food safety and health risk evaluation.

Home range is the spatial evolutionary arena where an individual can succeed or fail. Its size reflects the balance between individual energy requirements and acquisitions. Since various behavioural traits can affect individual energy demand, we investigated how these traits affect individual space-use behavior and resulting home range size of aquatic organisms. We compiled data for 172 freshwater and marine species, ranging from invertebrates to marine mammals, spanning 8 orders of magnitude in body size and 13 in home range size. Across all taxa, home range size scaled allometrically with body size (R 2 = 0.78, exponent = 1.68 ± 0.07). Behavioural traits explained an additional 27.15% of the variance beyond that explained by body size alone. In particular, carnivorous and pelagic species exhibited significantly larger home ranges than herbivorous and benthic ones, whereas migration and sociality were not retained as significant predictors beyond body size, despite migration affecting the intercept of the scaling relationship. We show that while body size is a strong predictor of home range, behavioural categories significantly modulate the allometric relationship. Our findings provide new insights into the behavioural constraints shaping spatial ecology in aquatic environments. These results underscore the role of energy-demanding behaviours in shaping spatial ecology, with implications for individual density, the intensity of intra-specific interactions, and patterns of interspecific coexistence.

High-fat diets (HFDs) are increasingly being studied in aquaculture because of their complex species-specific effects on fish physiology. While moderate fat levels can lower feed costs, supply essential fatty acids, and promote growth in some carnivorous and fast-growing species, excessive fat intake is linked to negative outcomes, such as impaired lipid metabolism, hepatic steatosis, immune suppression, and reduced growth. Although some studies have reported improved growth in zebrafish and other tolerant species, most finfish exhibited growth inhibition, metabolic dysfunction, and greater disease susceptibility under prolonged HFD exposure. Mechanistically, HFDs disrupt lipid homeostasis by downregulating lipolytic genes (e.g., cpt1a, pparα, and atgl) and upregulating lipogenic genes (e.g., srebp-1, fas, and acc), resulting in hepatic lipid accumulation. These shifts are associated with mitochondrial dysfunction, reduced fatty acid β-oxidation, oxidative stress, and activation of ER stress pathways such as ire1/xbp1. HFDs also stimulate inflammatory pathways through tlrs, nf-κb, and cytokines (il-6, tnf-α, and il-1β), contributing to immunometabolic imbalances. Additionally, HFDs negatively affect intestinal health by altering morphology, weakening barrier function, and disrupting microbiota composition, leading to poor nutrient absorption and increased infection risk. This review provides current evidence of HFD-induced changes in growth, immunity, lipid metabolism, mitochondrial function, and gut health in finfish. This emphasizes the importance of species-specific dietary fat optimization to improve feed efficiency, safeguard fish health, and ensure sustainable aquaculture practices.

Synthetic flavors from standardized processes have recently emerged as a promising and sustainable alternative to traditional feed attractants. In this study, two attractive (F25, cheese; F35, caramel) and one repulsive (F32-, coconut) synthetic flavors were individually added (1% w/w) to a commercial diet for European seabass (Dicentrarchus labrax) and tested over a 90-day feeding trial (30 fish per tank, in triplicate; initial weight 72.48 ± 8.04 g) to assess their impact on fish growth performance, welfare, and the modulation of brain appetite and monoaminergic pathways. None of the tested flavors negatively affected overall fish health. The F35 flavor enhanced feed intake (90.1 ± 5.6%) and growth (SGR 2.2 ± 0.2%) and positively influenced appetite-related and monoaminergic signals, thus being more effective than the F25 one (80.4 ± 3.2 and 1.6 ± 0.1%, respectively). A weekly feeding rotation between F35 and F25 (ROT group) resulted in suboptimal outcomes compared to F35 administration alone. The F32- flavor was not clearly perceived as strongly aversive by seabass and did not impair zootechnical performance. These findings highlight the potential of attractive synthetic flavors to improve diet palatability in a carnivorous species of commercial value, offering novel insights for more sustainable and cost-effective aquaculture feeding strategies.

Abstract Traditional livestock ranching impacts biodiversity by fragmenting and isolating habitats first as habitat loss, then as habitat isolation, affecting local fauna that occupies native habitats that rely on forest. In degraded areas, silvopastoral systems (SPS) are an agroforestry practice that integrates trees and livestock and they could provide new habitats for this fauna, though their effects are not well understood for Neotropical mammalian assemblages. This study assessed habitat selection and activity patterns in the Andes piedmont of Colombia. Using camera traps, we evaluated records in an intervened area, which was located around two fragments of native forest. A total of 17 mammal species were recorded, with 5 species using the SPS, of which Cerdocyon thous was exclusive to the SPS, whereas 12 species were found only in the forest, including six carnivorous species. Two anteater species showed overlapping activity in the forest but different patterns in the SPS. Despite more anteater records in the forest, both species selected the SPS. These results suggest that SPS could benefit certain species and alter interactions among Neotropical mammals.

The yellow-edged lyretail grouper, Variola louti, is ecologically and commercially important in the Red Sea. As a carnivorous species, V. louti plays a vital role in maintaining coral reef ecosystem health. Annually, an estimated 260 tonnes of V. louti are landed along the Saudi Arabian Red Sea coast, contributing approximately 6.5 million USD to the national economy. Given its significance, effective fishery management is crucial for sustainability. This study assessed the growth, maturity, and mortality of V. louti using fishery-dependent samples collected from the eastern Red Sea (February 2022–December 2024). Fork length (FL, n = 7,087) ranged from 10.5 to 64.3 cm, while total weight (W, n = 2,629) varied from 53 to 2,910 g. The FL–W relationship for both sexes combined was W = 0.0117×FL3.1. Von Bertalanffy growth parameters, based on sagittal otolith readings, were FL∞ = 62.28 cm, K = 0.12 year−1, and t0 = −2.26 years. Median FL at first maturity was 24.98 cm, with no significant sex differences. Mean natural mortality (M), derived from three different methods, was 0.243 year−1. Total mortality (Z), estimated using a linearized exponential decay model, was 0.38 year−1. Based on these Z and M estimates, fishing mortality (F) was calculated as 0.137 year−1. Yield-per-recruit and spawning potential ratio analyses indicate that the current F estimate places the stock near the target reference point. The current exploitation rate (E = 0.36) remains well below the limit reference point of 0.5. The V. louti fishery encompasses a broad FL range and multiple age groups, with immature individuals comprising less than 12% of total landings. However, according to the minimum landing size of 33 cm FL set by Saudi Arabian fisheries regulations, 47% of the total catch consisted of mature fish aged 2–3 years but below this threshold (25 cm ≤ FL < 33 cm), while only 41% met the legal-size requirement (FL > 33 cm). The high proportion of legally undersized individuals in landings underscores the need for ongoing monitoring and additional management measures, such as catch quotas, seasonal restrictions, and fishing effort reduction, to ensure long-term stock sustainability.

Gut microbiota and metabolic functions in herbivorous fish from Xisha coral reefs, China.

Small carnivorous fishes serve as important mesopredators in coral reef ecosystems. However, the habitat and prey availability degradation within these ecosystems has intensified the trend of body size miniaturization and interspecific competition among these species. To better understand the food selection and resource partitioning strategies of mesopredators, we conducted a comprehensive study on the feeding habits of four small carnivorous fish species collected from the coral reefs of the Nansha Islands. This study employed a combination of morphological analysis and molecular identification of gut contents, along with stable isotope analysis. Similar food items, mostly semi-digested/undigested body remains/fragments from crustaceans, fish, and mollusk were detected in the guts of the analyzed fishes. High-throughput sequencing based on DNA barcoding identified approximately 24 taxa belonging to Arthropoda, Chordata, and Mollusca, with Arthropoda being the most abundant prey group, accounting for 82.2%-92% of the total sequences across the four fish species. Stable isotope analysis further revealed that the trophic levels of the four species ranged from 3.4 to 3.6. The results of food overlap analysis based on stable isotopes contrasted with those obtained from high-throughput sequencing, highlighting the distinct characteristics and complementary strengths of these methods. This study broadens the current understanding of the feeding ecology of four carnivorous fish species. The findings reveal that crustaceans are the primary food source for carnivorous fishes in the Nansha Islands, differing from previous assumptions that their diets were predominantly fish-based. Additionally, the differentiated utilization of crustacean resources among these species suggests that marine benthic invertebrates may play a crucial role in supporting mesopredators within degraded coral reef ecosystems, potentially helping to mitigate the environmental stress they face.

Mercury biomagnification and microbial adaptation in a mining-impacted Amazonian River.

Drosera rotundifolia has one of the widest natural distributions of any carnivorous plant species, and is commonly associated with bogland habitats. New observations are presented of an ecologically unique population of D. rotundifolia growing on the gravely, poorly vegetated, slopes of an active volcano in Hokkaido, Japan. These field observations highlight the ecological plasticity of D. rotundifolia and indicate that under appropriate biotic and abiotic conditions, it can thrive in atypical habitats.

The modulation of mTOR signaling on dietary carbohydrate utilization in largemouth bass (Micropterus salmoides).

The carnivorous Drosera species employ hair-like appendages called trichomes that secrete a deadly adhesive consisting of an acidic polysaccharide, sugars, organic acids, and water to capture prey insects. Here, we develop a sustainable alternative to chemical pesticides using hyaluronic acid in a sugar-based natural deep eutectic solvent to mimic the composition and trapping mechanism of the Drosera mucilage. We formulate trichome biomimetic adhesives that become sprayable with added water to lower their viscosity, which can then regain the required adhesiveness as water evaporates up to the equilibrium content. Using a custom indentation setup, we measure promising adhesion energies between 9.5–14.5 µJ over one week, along with the formation of elongated fibrils (>2.3 cm) for the best-performing sample. Additionally, the material shows no phytotoxicity for over two weeks and effectively immobilizes western flower thrips through multiple contact points with the material in Petri dish bioassays, highlighting its efficacy and trapping mechanism akin to natural trichomes.