Predatory Fish Research Articles

Spatial and Ontogenetic Patterns in the Trophic Ecology of Two Predatory Fishes in a Large River

ABSTRACTFishes use a variety of physical and biological resources that shift ontogenetically, seasonally and spatially. Quantifying what resources such as prey are required for persistence can improve understanding of ecological needs of fishes and riverine macrosystem functioning. Bowfin (Amia ocellicauda) and largemouth bass (Micropterus nigricans) cohabitate in their native range and potentially compete with one another. Yet, there have been no direct comparisons of their diets across spatial gradients to assess whether they partition resources or shift in prey use. We used multiple univariate and multivariate analyses to compare diet composition, diet overlap, feeding strategy, prey importance and diet partitioning between largemouth bass and bowfin across three reaches of the Upper Mississippi River. Largemouth bass ontogenetically shifted their diet from aquatic invertebrates to fishes and a more diverse assemblage of aquatic invertebrates. Bowfin and adult largemouth bass were top predators which consumed mostly crayfish and fish and overlapped in their diets. Despite overlapping diets, predators partitioned resources by consuming different lengths and abundances of prey, and largemouth bass had greater trophic plasticity. Within a predator group, few differences in diets existed spatially, underscoring the relative homogeneity in resource use potentially from similarities in the river's physical structure. Combined, prey use likely differed sufficiently to reduce potential competition between largemouth bass and bowfin, allowing long‐term coexistence in this system. Our results also highlighted the importance of crayfishes to riverine food webs and underscored the use of multiple prey and habitat types that sustain these predators.

Comparative study of structural variations in gill rakers of different marine and freshwater herbivore and carnivore fishes

Comparative study of structural variations in gill rakers of different marine and freshwater herbivore and carnivore fishes

The effectiveness of crab apartment to shelter egg berried female of blue swimming crab (Portunus pelagicus) in Rembang, Central Java, Indonesia

Abstract Blue swimming crab is an Indonesian fishery commodity with high economic value for export to America, Asia, and Europe. The increase in crab fishing activities every year results in diminishing stocks in nature, in addition to predator attacks around spawning areas. The purpose of this study was to determine the growth of blue swimming crabs and identify types of fish in the crab apartment shelters in Rembang Regency, Central Java Province, from March to May 2023. The egg berried female crabs were put in a floating apartment for three months and monitored every 2 weeks to determine the growth of the hatched crab eggs. Our observations showed as many as 50 egg berried female crab with with an average size of 8–10 cm and a weight of 40–65 g. There were other marine organisms found in the shelter, including rabbit fish, shrimp, small crabs, and therapon-perch. Rabbit fish and therapon-perch often result in reduced juveniles. Therefore, add and installing shelter is highly recommended to the entry of these fish. This study found crab apartment brings positive impacts on the survival of hacthing crabs and protected them from the threat of predatory fish.

How Japanese eels escape from the stomach of a predatory fish

Predation shapes diversity in the defensive tactics of prey. One specialized defensive tactic is to escape the digestive system of the predator after capture1,2,3,4,5,6,7,8. While most of these defensive tactics involve passive ejection alive from predators' mouths and vents1,2,3,4,5, active escape from the digestive tracts of predators has recently been observed in certain invertebrate species6,7 and fish8. However, no study has yet uncovered the behavioral patterns and escape routes of the prey within a predator's digestive tract. Here, we report the sequential escape processes of the Japanese eel Anguilla japonica from capture to escape via the gills of predatory fish Odontobutis obscura using an X-ray video system. All captured eels had at least one portion of their bodies swallowed into the stomach of the predator. Surprisingly, after being swallowed, most individuals attempted to escape by going back up the digestive tract towards the esophagus and gill, and some of them succeeded in escaping via the predator's gill. Some eels, whose entire bodies were completely inside the stomach, exhibited circling behavior along the stomach, seemingly searching for possible escape routes. An electro-anesthetization experiment revealed that eels utilize various escape routes through gill clefts, rather than just one.

The natural diet of Prolatilus jugularis inhabiting Lessonia trabeculata kelp forests of south-central Chile

Kelp forests support species-rich food webs that predator-prey interactions may sustain. Here, we analyze prey availability and stomach contents of the predatory fish Prolatilus jugularis in an unexplored subtidal kelp forest of Lessonia trabeculata in south-central Chile. In the kelp forest, 42 invertebrate taxa and 1016 individuals were observed. In the diet of P. jugularis, 21 taxa and 130 individuals were identified. Crustacea, particularly amphipods, were the dominant and more frequent taxa in the kelp forest and stomach contents. Annelida and Mollusca were also present in the kelp forest and diets but were less abundant. We did not find a statistically significant correlation between kelp forest and stomach-content prey abundances and frequencies. Also, dominance structure significantly differed between kelps and stomach contents. Our results indicate that P. jugularis could feed in other habitats outside the survey area. Seven predatory fish were sampled in the kelp forest. Pinguipes chilensis was the dominant fish, with 65% of the total fish biomass, followed by P. jugularis with 20%.

Genetic Diversity of Bluefish Population in Türkiye Coastal

Bluefish (Pomatomus saltatrix) is a commercially important, highly migratory predatory fish species distributed along the coasts of Türkiye. Conservation and sustainability of bluefish populations requires knowledge of the genetic structure of the population, but There are no genetic studies on bluefish in Türkiye. In this study, the population structure of Bluefish in the coastal regions of Türkiye was investigated by sequence analysis of mitochondrial DNA gene regions (Cytochrome b and Displacement-loop) and nuclear gene region (Rhodopsin). We tried to identify bluefish samples collected from 14 regions in the coastal region of Türkiye by analyzing two mtDNA gene sequences (Cyt b and D-loop) and nuclear gene region (Rhodopsin). While a total of 35 haplotypes were found in the Cytb gene region, a total of 132 haplotypes were found in the D-loop (control region) gene region. A single haplotype was detected in all stations for Rhodopsin. Also, the maximum likelihood trees based on Cyt b and D-loop sequences suggested relationship of Bluefish populations from Türkiye and the world. Results showed a low level of genetic differentiation between Bluefish populations in the study area, but Aegean and Mediterranean populations are more diverse than other populations due to migratory trait of this species.

Myxobolus dabryi n. sp. (Myxozoa: Myxobolidae) Infecting the Gills of Chanodichthys dabryi, Bleeker, 1871 (Cypriniformes: Cyprinidae) in Hunan Province, China.

Culters are a popular and economically important carnivorous freshwater fish, widely distributed in rivers, lakes, and reservoirs in China. An investigation of Myxozoa was conducted to enhance the understanding of Myxozoan diversity in Culters in China, as only 15 Myxosporean species have been previously reported in 6 Culters species. A new species with typical Myxobolus characteristics was discovered exclusively in the gills of Chanodichthys dabryi, Bleeker, 1871, and no other species were found in other Culters fish or organs. The new species elicited whitish plasmodia in the serosa layer of the gill arch, with no distinct inflammatory reaction observed. This species is morphologically different from all reported Myxobolus spp. from Culters, differing in plasmodium and spore size, as well as the coils of polar filaments. Molecular analysis further supports that it does not match any sequences available in GenBank. Therefore, we identified it as a new species and named it Myxobolus dabryi n. sp.

Resilience to changes in salinity and predator diversity in representative Gulf of Mexico estuarine fish predator-prey interactions

Predators strongly influence ecological communities and subsequent ecosystem function by directly consuming prey individuals and indirectly by inciting alterations in prey behavior, termed non-consumptive effects (NCEs). Gulf of Mexico estuaries support complex food webs structured by numerous species interactions maintained in constant environmental flux from variation in salinity. Environmental variation presents a source of physiological stress for estuarine fish and plays a role in their distributions and subsequent interactions. Here, we present the results of a mesocosm experiment examining if acute changes in salinity disrupt NCEs of different predators on estuarine prey. We exposed Gulf killifish (Fundulus grandis) to visual and/or olfactory cues from a common estuarine predator, red drum (Sciaenops ocellatus), and from a freshwater predator that is a transient species in lower portions of estuaries, largemouth bass (Micropterus salmoides), under either decreasing, constant, or increasing salinity. Killifish decreased shoal size and movement in response to olfactory cues or both visual and olfactory cues compared to when they were exposed to no cues or visual cues, demonstrating variable perceived risk dependent on cue type. Behavioral response did not vary by predator species, implying a generalized response to different fish predators. Prey did not change behavior when exposed to decreasing salinity compared to constant salinity. However, prey movement increased with increasing salinity, indicating that salinity changes may provide cues to search for different habitats instead of a stressor. Our experiment indicates that estuarine predator-prey interactions may be resilient to acute salinity changes given the broad tolerances of euryhaline species.

Biosynthesis of long-chain polyunsaturated fatty acids in the nereid polychaete Hediste diversicolor: Molecular cloning and functional characterisation of three fatty acyl elongases and two front-end desaturases

Aquaculture of carnivorous fish species heavily relies on marine ingredients to guarantee the provision of essential nutrients, including long-chain (C20–24) polyunsaturated fatty acids (LC-PUFA) such as arachidonic acid (ARA, 20:4n-6), eicosapentaenoic acid (EPA, 20:5n-3), and docosahexaenoic acid (DHA, 22:6n-3). These nutrients are crucial for fish growth and neural development, offering significant health benefits to consumers. The rapid growth of global aquaculture production in recent decades, has driven the exploration of alternative and sustainable feeding sources that ensure n-3 LC-PUFA content. Within the context of circular economy, polychaete worms arise as promising candidates for aquafeed formulations, due to the enzymatic capacity for de novo LC-PUFA biosynthesis. The present study focused on the molecular and functional characterisation of elongases (Elovl) and front-end desaturases (Fed) involved in the LC-PUFA biosynthesis of the nereid polychaete Hediste diversicolor. The sequence and phylogenetic analysis established the orthology of three Elovl, identified as Elovl2/5, Elovl4 and Elovl1/7, that have putative functions in the LC-PUFA biosynthesis. Functional characterisation in yeast demonstrated their roles as PUFA elongases, exhibiting affinity towards C18 and C20 PUFA substrates (Elovl2/5) and towards C18, C20 and C22 (Elovl4 and Elovl1/7). Additionally, H. diversicolor possesses two front-end desaturases (Fed1 and Fed2) with Δ5 and Δ6/Δ8 desaturation activities, respectively, thus encompassing all the necessary desaturation reactions involved in the LC-PUFA biosynthesis pathways. These findings, along with the previously characterised methyl-end desaturases, show that H. diversicolor possesses the full enzymatic repertoire necessary to produce LC-PUFA like ARA and EPA. This highlights the potential of polychaetes and other annelids for producing nutrient-rich biomass suitable for aquaculture.

Identification of body coloration related genes in ricefield eel (Monopterus albus) using GWAS

Body color is one of the most diverse external morphological characteristics of fish. It not only affects the function of fish predation and individual communication but also has important economic value. The ricefield eel (Monopterus albus) is a popular freshwater aquaculture fish species in China. Few studies have suggested some candidate genes involved in the formation of body color in this fish; however, further genetic evidences are required. Genome-wide association analysis (GWAS) is a powerful analytical method for identifying relationships between target traits and genetic markers or candidate genes in natural populations. In this study, two populations of ricefield eel with different body coloration were used to study the genetic factors that regulate the formation of body color. Through GWAS, 67 SNPs, 463 genes and 5 signaling pathways were found to be associated with body color. These results suggest that a complex molecular regulatory mechanism regulates ricefield eel body coloration. Our findings lay the foundation for subsequent genome selection breeding of ricefield eel.

Phenotypic and behavioral variation as a mechanism behind the invasive potential of a predatory neotropical fish

Phenotypic and behavioral variation as a mechanism behind the invasive potential of a predatory neotropical fish

PI3KR1 and AKT1 in largemouth bass (Micropterus salmoides): molecular cloning, characterization, and its involvement in the alleviation of hepatic glycogen deposition caused by insulin inclusion in vitro.

In this study, the full-length cDNA sequences of the phosphatidylinositol-3-kinase p85 alpha (PI3KR1) and serine/threonine kinase 1 (AKT1) genes in largemouth bass (Micropterus salmoides) were obtained using the rapid amplification of cDNA ends (RACE) method. Sequence analysis revealed that the cloned sequences of PI3KR1 and AKT1 are 4170 bp and 3672 bp in length, with open reading frames (ORFs) of 1389 bp and 1422 bp encoding 462 and 473 amino acids, respectively. Sequence alignment and evolutionary tree analysis indicated their close relationship to other teleosts, especially those with similar feeding habits. Tissue distribution demonstrated widespread distribution of both genes in various tissues, with the highest abundance in the liver. Further results found that the upregulation of the expression of p-PI3KR1, p-AKT1, p-FoxO1, and GLUT2 proteins by insulin, while suppressing the expression of the total FoxO1 protein, effectively triggers a significant activation of the PI3KR1-AKT1 insulin signaling pathway. Meanwhile, the mRNA levels of the key glycolytic genes, including glucokinase (gk), pyruvate kinase (pk), and phosphofructokinase liver type (pfkl), have been enhanced evidently. In contrast, the expression of gluconeogenic genes such as phosphoenolpyruvate carboxykinase (pepck), glucose-6-phosphatase catalytic subunit (g6pc), and fructose-1,6-bisphosphatase-1 (fbp1) has been notably down-regulated. In addition, insulin treatment promoted the phosphorylation of glycogen phosphorylase (PYGL) and the dephosphorylation of glycogen synthase (GS), and the glycogen content in the insulin-treated group was remarkably reduced compared to the control group. Overall, our study indicates that the activation of PI3KR1-AKT1 insulin signaling pathway represses the hepatic glycogen deposition via the regulation of glycolysis and gluconeogenesis, which provides some new insights into nutritional strategy to effectively regulate the glucose metabolism in carnivorous fish.

Environmental DNA Reveals the Impact of Submarine Groundwater Discharge on the Spatial Variability of Coastal Fish Diversity.

Submarine groundwater discharge (SGD) has recently been recognized as an influential factor in coastal ecosystems; however, little research has been conducted on its effects on coastal fish diversity. To investigate the relationship between SGD and fish diversity, we conducted a survey at the coastal island scale using the environmental DNA (eDNA) method. Our findings indicate that fish species richness and functional richness peak at stations with high SGD. Environmental variables, such as salinity, dissolved inorganic nitrogen (DIN) concentration, and SGD, significantly influence fish diversity. Carnivore fish richness was negatively correlated with salinity, while planktivore fish richness was positively correlated. Additionally, SGD and DIN concentrations were found to be crucial in shaping omnivorous and pelagic communities, respectively. This study highlights the role of SGD in enhancing nutrient conditions favorable for diverse fish communities and demonstrates the effectiveness of eDNA metabarcoding for rapid marine biodiversity assessment. These findings provide valuable insights for coastal ecosystem monitoring and management.

Effect of different feeding regimens on physiological indicators, intestinal transcriptome, and bacterial flora of mandarin fish (Siniperca chuatsi)

Mandarin fish (Siniperca chuatsi) represents a typical carnivorous freshwater economic fish in China. Recently, the study of their feeding behavior to acclimate formulated diets has become a research focus. This study evaluated the effects of various diets on the body composition, nutritional content, digestive enzyme activity, gene expression, and gut microbiota of mandarin fish. Firstly, no significant differences were found in the muscle's basic nutritional components (moisture, crude protein, crude fat, and crude ash), as well as in the fatty acid and amino acid content, between the live feed group (LFSC) and the compound feed group (CFSC). However, mandarin fish in the LFSC group exhibited significantly higher lipase activity in the liver and intestine compared to the CFSC group, while amylase activity in the intestine showed an opposite pattern. Additionally, intestinal transcriptome analysis revealed 6238 differentially expressed genes and identified several differentially expressed clock genes associated with diet type. Furthermore, gut microbiota analysis indicated that different feeding regimens influenced microbial composition, revealing correlations between bacterial genera and intestinal gene expression levels. These findings provided novel insights into the gut microbiota and transcriptomic responses of mandarin fish to different dietary types.

Effect of Natural Feeding Capacity of Dengue Mosquito (Aedes aegypti) Larvae and Different Stocking Densities of Gold Molly Panda Fish (Poecilia spp) on the Feeding Speed and Function of Natural Predators in Gold Molly Panda Fish (Poecilia spp)

Effect of Natural Feeding Capacity of Dengue Mosquito (Aedes aegypti) Larvae and Different Stocking Densities of Gold Molly Panda Fish (Poecilia spp) on the Feeding Speed and Function of Natural Predators in Gold Molly Panda Fish (Poecilia spp)

Learning obstacle avoidance and predation in complex reef environments with deep reinforcement learning

The reef ecosystem plays a vital role as a habitat for fish species with limited swimming capabilities, serving not only as a sanctuary and food source but also influencing their behavioral tendencies. Understanding the intricate mechanism through which fish adeptly navigate the moving targets within reef environments within complex water flow, all while evading obstacles and maintaining stable postures, has remained a challenging and prominent subject in the realms of fish behavior, ecology, and biomimetics alike. An integrated simulation framework is used to investigate fish predation problems within intricate environments, combining deep reinforcement learning algorithms (DRL) with high-precision fluid-structure interaction numerical methods-immersed boundary lattice Boltzmann method (lB-LBM). The Soft Actor-Critic (SAC) algorithm is used to improve the intelligent fish's capacity for random exploration, tackling the multi-objective sparse reward challenge inherent in real-world scenarios. Additionally, a reward shaping method tailored to its action purposes has been developed, capable of capturing outcomes and trend characteristics effectively. The convergence and robustness advantages of the method elucidated in this paper are showcased through two case studies: one addressing fish capturing randomly moving targets in hydrostatic flow field, and the other focusing on fish counter-current foraging in reef environments to capture drifting food. A comprehensive analysis was conducted of the influence and significance of various reward types on the decision-making processes of intelligent fish within intricate environments.

Awareness and perceptions of contaminants in the Dehcho and Sahtú Regions of the Northwest Territories

ABSTRACT The development and dissemination of health messaging is a critical component of reducing health disparities. Participants (n = 87) from a human biomonitoring study in six Dene communities responded to a survey about health communication regarding contaminants. The survey included questions on awareness of health messages and risk perceptions related to country foods and contaminants. The vast majority of participants reported eating country foods (99%) and heard that country foods had beneficial nutrients (90%). Seventy per cent of respondents had heard or seen messages about fish with high levels of mercury, and 60% had concerns about the safety or quality of country foods they consumed. Respondents who reported decreasing the number of fish they ate since hearing the messages about fish and mercury had lower (p = 0.04) mercury concentration in hair, compared to those who had not heard the messages. However, no differences in hair mercury were observed for respondents who reported to have changed their fishing location, chosen smaller fish or eaten less predatory fish since hearing the messages. Results indicate the need to examine reasons for self-reported behaviour changes, in addition to awareness. The conclusions of this study can inform the development of messaging and risk management decisions about contaminants within Indigenous populations.

Efficiently Substituting Dietary Fish Meal with Terrestrial Compound Protein Enhances Growth, Health, and Protein Synthesis in Largemouth Bass.

Inappropriate substitution of dietary fishmeal (FM) can adversely affect the growth, health, and metabolism of carnivorous fish species. To effectively reduce the amount of dietary FM in carnivorous largemouth bass (Micropterus salmoides), a terrestrial compound protein (Cpro) with chicken meal, bone meal, and black soldier fly protein was used to formulate four isoproteic (52%) and isolipidic (12%) diets, namely T1 (36% FM), T2 (30% FM), T3 (24% FM), and T4 (18% FM), for feeding juveniles (initial weight: ~12 g) for 81 days. Results indicated that the growth performance, feed efficiency, and morphological indicators, as well as muscle texture and edible quality of fish, did not differ significantly among the four groups. However, the muscle protein contents and ATP/AMP ratio of fish in the T4 group were significantly increased in comparison with those of fish in the T1 group, while the opposite was true for muscle glycogen. Compared with the T1 group, high serum total amino acid and MDA contents, as well as low AST activities, were observed in the T3 and T4 groups, and relatively high intestinal trypsin and lipase activities were found in the T2-T4 groups. The transcripts of intestinal proinflammatory cytokines (il-1β, il-6, and tnf-α) were downregulated in the T2-T4 groups compared with T1 group, while the expression of anti-inflammatory cytokines (il-10) and tight junction (zo-1 and occludin) showed the reverse trend. The mRNA expression of positive regulators related to protein synthesis (sirt1, pgc1-α, pi3k, and akt) were significantly upregulated in the muscle of fish fed diets T3 and T4, while their negative regulators (4e-bp1) mRNA levels were downregulated. The results indicate that the dietary FM of largemouth bass could be effectively reduced to at least 18% by the Cpro, which is beneficial to health, digestion, and protein synthesis for maintaining accelerated growth.

Yinchenhao Decoction mitigates intestinal impairment induced by high carbohydrate diet in largemouth bass (Micropterus salmoides): insights from inflammation, apoptosis, oxidative stress, tight junctions, and microbiota homeostasis.

As a major source of energy, carbohydrates have a protein-saving effect. However, excessive consumption of carbohydrates can lead to the disruption of the intestinal barrier in fish, especially for carnivorous fish. Therefore, traditional Chinese medicine component Yinchenhao Decoction (YD), was used to detect the effect on intestinal barriers and microbial community equilibrium for largemouth bass in current research. In this research, a series of NC (normal carbohydrate diet) and HC (high carbohydrate diet) with graded YD treatments during 10 weeks feeding trial. Results suggested that 2% and 4% YD treatments significantly reduced gut inflammation and mucosal loss caused by HC. Compared with NC, HC significantly decreased the relative expression of intestinal tight junction-related genes (zo1, claudin1, claudin7, and occludin). However, with the application of YD, the expression of tight junction-related genes (zo1, claudin1, and claudin7) increased significantly (p < 0.05). Likewise, administration of YD significantly reduced elevated plasma diamine oxidase (DAO) activity caused by HC (p < 0.05). Additionally, YD significantly downregulated the mRNA expression of endoplasmic reticulum stress (ERS)-related genes (grp78, atf6, chopα, ire1, xbp1, and eifα) and pro-apoptosis genes (casp3, casp8, and bax) (p < 0.05), while upregulating the anti-apoptosis gene bcl2 (p < 0.05). Moreover, YD significantly increased the mRNA expression of antioxidant genes and the enzyme activities of CAT and GPX, while decreased MDA concentration significantly (p < 0.05). Whereas, YD markedly decreased the expression of pro-inflammatory genes (il1β, tnfα, il8, and nf-κB) and the immune enzymes activity (ACP and AKP) (p < 0.05) by up-regulating the expression of anti-inflammatory genes (ikb and il10). Notably, YD modulated the largemouth bass intestinal microbial community, enhanced the diversity and increased the abundance of probiotic microorganisms in the intestinal microbiota. In summary, YD supplementation in HC alleviated inflammation, apoptosis, oxidative stress, tight-junction injury, and microbiota disequilibrium in the intestine, which suggested that YD could be a valuable functional additive in aquaculture.

Background selection for camouflage shifts in accordance with color change in an intertidal prawn.

To maximize camouflage across visually heterogeneous habitats, animals have evolved a variety of strategies, including polyphenism, color change, and behavioral background matching. Despite the expected importance of behavioral processes for mediating camouflage, such as selection for matching substrates, behavior has received less attention than color traits themselves, and interactions between color change and behavior are largely unexplored. Here, we investigated behavioral background matching in green and red chameleon prawns (Hippolyte varians) over the course of a color change experiment. Prawns were housed on mismatching green and red seaweeds for 30 days and periodically given a choice test between the same seaweeds in y-choice trials over the experiment. We found that, as prawns change color and improve camouflage (to the perspective of a fish predator), there is a reinforcing shift in behavior. That is, as prawns shift from red to green color, or vice versa, their seaweed color preference follows this. We provide key empirical evidence that plasticity of appearance (color) is accompanied by a plastic shift in behavior (color preference) that reinforces camouflage in a color changing species on its natural substrate. Overall, our research highlights how short-term plasticity of behavior and longer-term color change act in tandem to maintain crypsis over time.