Stomach Content Analysis Research Articles

Does tagging transparent fish increase predation risk? A laboratory study with glass eel (Anguilla anguilla) and sea bass (Dicentrarchus labrax).

Barriers in the estuaries of the rivers prevent the immigration of glass eels (Anguilla anguilla) arriving on the European coast every spring. This leads to an unnatural accumulation of migrating glass eels below the barriers, and this may lead to additional losses in glass eels by piscivorous fish. The proportion of predation losses can be estimated using mark‐recapture techniques and abundance estimates in combination with stomach content analysis of piscivorous fish. Nonetheless, whether tagging transparent glass eels increases predation risk and what the digestion rate of glass eel is in piscivorous fish are unknown. This study aimed to determine whether there is an increased predation risk for tagged glass eel; it also studies glass eel digestion status in piscivorous fish after appointed time frames. A laboratory experiment with 48 trials was conducted. Tagged (visible implanted elastomer, VIE) and untagged glass eels were exposed to small (19.1–24.4 cm) and large (31.9–43.5 cm) sea bass (Dicentrarchus labrax) during a 2 h trial. In 48% of the trials, successful predation was present and 13% showed clear predation attempts in which bass did not capture glass eels. No significant difference was found in predation rate between tagged and untagged glass eels and between red and blue tagged glass eels. Large sea bass predated more, but all sizes consumed glass eel under laboratory conditions. Stomach content analysis showed intact glass eel bodies 4–6 h after ending the 2 h trial and parts of glass eel bodies up to 16–18 h. This study showed that tagging does not increase predation in mark‐recapture studies using VIE‐tags in transparent glass eel. It also shows that the proportion of predation in relation to local glass eel abundance can be estimated if stomach content analysis is conducted within 4–6 h after predation.

Invasion Risk and Potential Impact of Alien Freshwater Fishes on Native Counterparts in Klang Valley, Malaysia.

Simple SummaryThe mechanisms on how alien species naturally affect the native species in the real aquatic environment are infrequently studied. This study explores the potential effects of alien fishes on the native fish community, well-being, and trophic preferences in selected rivers of Klang Valley, Malaysia. We found that alien fishes benefited from the impacts of anthropogenic activities in their surrounding habitats, while their plasticity in feeding habits might help them to invade, survive, and dominate. This study revealed the natural mechanisms on the establishment of alien fish species and their potential ecological impacts on native fishes in the rivers of Klang Valley, Malaysia.This study explores the potential effects of alien fishes on the native fish community, well-being, and tropic preferences in selected rivers of Klang Valley, Malaysia. Following the Aquatic Species Invasiveness Screening Kit assessment, most of the alien fishes (80%) are invasive. The alien species occurrences correlated positively (p < 0.05) with poor water quality, such as rivers with high ammonia-nitrogen and nitrite, but negatively with phosphate and dissolved oxygen. Anthropogenic characteristics, such as rivers with high pollution levels and ease of accessibility to the fish habitat, are mainly associated positively (p < 0.05) with the occurrences of alien fish species. In general, the results of fish stomach contents analyses and their associated indices, together with stable carbon and nitrogen isotopes, revealed domination by alien fishes or diet overlaps between both alien and native fish species. This finding indicates that alien fishes benefited from the impacts of the anthropogenic activities in their surrounding habitats, while their plasticity in feeding habits might help them to invade, survive, and dominate in the rivers of Klang Valley, Malaysia.

Seasonal trophic ecology of the invasive crab Percnon gibbesi (Brachyura, Plagusiidae) in the southwestern mediterranean: Insights from stomach contents and stable isotope analyses

The invasive sally lightfoot crab Percnon gibbesi (H. Milne Edwards, 1853) has spread among the coasts of the Mediterranean Sea, including the coasts of Annaba Gulf (Algeria). Investigating the trophic position of the species and looking for the seasonal variations in the diet of this alien decapod was the aim of this study. To do this, samples of P. gibbesi were collected along Annaba coasts within a year. The traditional stomach content analysis (SCA) was integrated to the stable isotope analysis (SIA) of nitrogen and carbon to provide a comprehensive evaluation of the feeding ecology of P. gibbesi, and its within-year variability. Results highlighted, for the first time, significant seasonal variation in P. gibbesi diet, improving our understanding of its trophic plasticity and potential dietary overlaps with other herbivore species. Its feeding plasticity is an asset in the successful expansion of its distribution. Relating its diet composition through the different seasons with the interactions with native herbivores will be essential to fully appreciate the impact of the spread of P. gibbesi in the Mediterranean Sea.

Juvenile Silver Carp and Bighead Carp as Forage for Predatory Fish in the LaGrange Reach of the Illinois River

AbstractIncreasing numbers of Silver Carp Hypophthalmichthys molitrix and Bighead Carp H. nobilis (commonly called “bigheaded carp”) in the Illinois River have led to concerns about the impact that their invasion has on native food web dynamics. Bigheaded Carp recruited in large numbers in the LaGrange Reach of the Illinois River during the summer of 2014. This provided an opportunity to determine whether native piscivorous fish prey upon invasive carp when they are abundant. Using electrofishing and fyke nets in the LaGrange Reach (August 1–November 8, 2014), we sampled native predatory fish (n = 1,472) for stomach content analysis. Fish community data from the Upper Mississippi River Restoration Program’s Long‐Term Resource Monitoring was used to quantify prey abundance (fish &lt; 100 mm) in the study area and indicated that bigheaded carp represented 9% of available prey. Stomach content analysis revealed that the frequency of occurrence of juvenile bigheaded carp was greater than 15% in Shortnose Gar Lepisosteus platostomus, White Bass Morone chrysops, Black Crappie Pomoxis nigromaculatus, Channel Catfish Ictalurus punctatus, Smallmouth Bass Micropterus dolomieu, Largemouth Bass Micropterus salmoides, White Crappie Pomoxis annularis, Yellow Perch Perca flavescens, Flathead Catfish Pylodictis olivaris, Freshwater Drum Aplodinotus grunniens, and Yellow Bass Morone mississippiensis. Predators sampled in August and September foraged more heavily on juvenile bigheaded carp than those sampled in October and November. Electivity analysis suggested that juvenile bigheaded carp were selected over native forage by White Bass, Black Crappie, and Shortnose Gar, as these predators continued consuming them even as availability declined. Our results imply that native piscivores in the Illinois River consume and sometimes prefer juvenile bigheaded carp as prey. These results suggest that native predators might play a role in regulating bigheaded carp recruitment and that negative impacts to predators in areas of dense carp populations might be somewhat mitigated by the consumption of juvenile bigheaded carp.

Dietary niche breadth of endemic and introduced anurans (Amphibia: Anura) in Lombok, Lesser Sunda Islands– Indonesia

Anurans are important organisms as components of faunal community structure in ecosystems because of their roles as secondary and tertiary consumers in food webs. Anurans are opportunistic organisms that will consume any resources in their habitat. In this study, we dissected thirty-nine specimens of anurans from Museum Universitas Mataram (MUM) reference collection, it consists by three endemic (Ingerophrynus biporcatus, Limnonectes dammarmani and L. kadarsani) and one introduced species (Duttaphrynus melanostictus) of anurans. These reference collections were collected by authors during herpetofauna survey at Pusuk Forest, western Lombok in 2018. Based on stomach content analysis, both endemic and introduced anurans are generalist arthropod predators where hymenoptera, coleoptera, orthoptera and chilopoda are the most important food. In this study, we found positive correlations between body size and dietary niche breadth in which each anuran species has a high overlap of dietary niches. Anurans with large body size have a variety of prey than the small one.

Trophic Ecology of Juvenile Southern King Crab Associated with Kelp Forest: Evidence of Cannibalism

The southern king crab, Lithodes santolla, is a well-known predator/scavenger species during its adult phase but its feeding strategy in early stages is less studied. This information is important to understand their role in ecosystems and to improve fishery management (i.e., stock enhancement). Based on stomach contents and stable isotope analysis, we determined variation in the composition of diet and niche overlap in vagile and cryptic phase collected within and outside a kelp forest, Macrocystis pyrifera, of Aguila Bay at the Magellan Strait in Patagonia, Chile. Results of juvenile stomach content analysis showed 60% dissimilarity between cryptic and vagile juvenile phases. Algae dominated the volumetric contribution in cryptic juveniles while crustacean dominated the diet in vagile phase. Exoskeleton of other king crabs occurred in 43% of juveniles with crustaceans in their stomach. This fact confirms cannibalistic behavior in the wild in this species, which is consistent with findings in massive laboratory cultures. There was no evidence of isotopic niche shift between cryptic and vagile juvenile phases. Overlapping isotopic niches of different-sized juveniles suggest that they exploit similar food resources. However, vagile individuals occupy a higher trophic position than cryptic individuals, which could suggest a switch in dietary preference, from detritivorous/herbivory within kelp forests to omnivory outside of kelp forests, and an increase in the level of cannibalism in vagile juveniles.

The Diet of a Roosting Population of Asian Glossy Starling Aplonis panayensis in Jelebu, Negeri Sembilan, Malaysia

Communal roosting by urban birds, such as crows, mynas, and starlings, can be a public nuisance due to excessive noise and fouling of the surroundings with droppings. Food availability within proximity to the roosting area is one of the key factors influencing roosting site preference and fidelity. The diets of roosting mynas and crows have been well-studied, yet little is known about the diet of the Asian glossy starling (AGS), Aplonis panayensis. This study focused on assessing the diet of roosting AGS and food resource availability around the roosting area. The AGS diet was assessed through microscopic analysis of stomach contents and droppings. The diet mainly consisted of fruits (76%) with a minor component of animal materials, i.e. ants, snails, and beetle larvae. Intact seeds found in the samples were identified using DNA barcoding. Seven out of the nine plant species detected were new records for the AGS diet. The most common fruit found in the samples was Trema orientalis, which grows extensively along roadsides within foraging areas of AGS. The availability of fruits of different fast-growing pioneer species around the roosting site ensured a continuous supply of food to the birds. Animal materials, which were consumed by chance during foraging, supplemented the fruit in the bird’s diet. Hence, the birds’ preference for the roosting site may have been influenced by the availability of various food resources around it.

Advances in the study of the trophic niche of batoids with distribution in Mexican waters

AbstractBatoid (rays and skates) populations are declining worldwide, with unknown ecological consequences due to lacking consolidated data on the trophic ecology of these species. Such trends are particularly disconcerting in Mexican waters, where batoids are heavily exploited by commercial fisheries. To assess the current state of knowledge of batoid diet in this region, we conducted a meta‐analysis of 54 published stomach content analysis studies. Trophic niche was assessed from 44 total species, including variations due to sex, ontogeny, season, and region, as well as trophic overlap among species. The species assessed belonged to the taxonomic families Urotrygonidae, Dasyatidae, Potamotrygonidae, Mobulidae, Rhinopteridae, Aetobatidae, Gymnuridae, Rhinobatidae, Rajidae, Arhyncobatidae, and Narcinidae. Most of the diet studies to date were conducted in the Mexican Pacific (n = 24), whereas only three studies have come from the Mexican Atlantic, with 27 additional studies coming from other American countries from the tropical and subtropical region. Crustaceans were reported in more than 50% of the species assessed and were also generally the most important prey item, with either high (76%–100%) and medium‐high (51%–75%) importance based on dietary indices from the literature reviewed. While the diet of 40 species (91%) consisted of more than one prey type, feeding strategy analysis (Levin and Shannon–Wiener indices) of 27 species indicated that 25 were specialists and two generalists. Species diets varied with ontogeny (20%), sex (11%), region (11%), and seasonality (9%). According to the reviewed studies, interspecific diet overlap was evident in 36% of species, mainly in the family Urotrygonidae. Batoids were grouped into four trophic guilds: crustacivores (68.1%), annelidivores (primarily polychaetes) (13.6%), molluscivores (11.3%), and piscivores (6.8%), based on the literature reviewed. This study showed that most of the batoids had a specialist crustacean‐based diet. Future research should focus on species devoid of dietary data to encapsulate the trophic niche breadth of this group in Mexican waters, particularly from the Mexican Atlantic and surrounding regions.

Factors Influencing Dietary Changes of Walleye Pollock, Gadus chalcogrammus, Inhabiting the East Sea off the Korean Coast

This study examined the dietary patterns of walleye pollock, Gadus chalcogrammus, off the middle eastern coast of Korea between January 2016 and December 2017 to determine the influences of various predictors on dietary changes. Based on stomach content analyses, walleye pollock was found to be a demersal carnivore that mainly consumes carid shrimps, euphausiids, mysids, teleosts, and cephalopods. The main prey species identified in the diets of walleye pollock were Euphausia pacifica (euphausiids), Themisto japonicus (amphipods), Neomysis spp. (mysids), Neocrangon communis, Pandalus borealis (carid shrimps), Watasenia scintillans (cephalopods), and Bothrocara hollandi (teleosts), which are hyper-benthic and bentho-pelagic organisms. Dietary analyses based on the weight contributions of different prey taxa to the diets revealed significant variations in dietary composition in terms of fish size, water depth, and season, implying intraspecific dietary segregation. Euphausiids dominate the diets of smaller individuals (&lt;30 cm TL), whereas the contributions of carid shrimps, teleosts, and cephalopods increase as body size increases. Similarly, the latter three prey items are dominant food resources in deeper habitats. The PERMANOVA results revealed that the size-related spatial and temporal changes in dietary composition are all significant for the species, as well as their two- or three-way interactions among those factors, except for the size-depth interaction. The coupling effect of size and depth is indicative of depth-dependent differences in fish sizes, with the tendency for larger individuals to be distributed in deeper habitats. In addition, seasonal and interannual variations in water column structures are also evident in the diets, which may, in part, account for the diet seasonality observed in the stomach content analysis. The dietary analyses of walleye pollock will improve our understandings to seek functional role of the species in benthic food webs, and to predict the effects of environmental and anthropogenic perturbations.

Trophic ecology of the Hubb's octopus Octopus hubbsorum (Cephalopoda: Octopodidae) in the central Mexican Pacific

ABSTRACT The diet of the Hubb's octopus Octopus hubbsorum along the coast of Acapulco, Guerrero, Mexico, was determined by analysing the stomach contents of 413 individuals collected monthly between February 2017 and March 2018. Most stomachs (74.3%) presented contents, while 25.7% were empty. Sixty prey items were identified and grouped into 16 categories. The most frequent prey items were Petrolisthes sanfelipensis, Clastotoechus diffractus, Petrolisthes hians and Alpheus spp. Smith's index indicated that O. hubbsorum follows a generalist diet for each hydroclimatic season, sex and size class (1: juvenile; 2: young adult; 3: mature adult). Cannibalism was frequent among males, less so among females. Pianka's index revealed a higher overlap among the three size classes of both sexes during the dry season, while during the rainy season the overlap was reduced for size classes 2 and 3 in both sexes. The average isotopic values overall were δ13C −14.96‰ (±0.08) and δ15N 13.02‰ (±0.09). A significant difference (P = 0.005) was observed in δ13C among hydroclimatic seasons (rainy and dry) and size classes, while for δ15N a significant difference (P = 0.013) was observed between seasons. Stomach content analysis gave values of the trophic position of O. hubbsorum ranging from 3.57 to 3.72, whereas the values obtained using stable isotope analysis, using δ15N, ranged from 3.52 to 3.86. Variation was observed in isotopic niche size and Layman's metrics among hydroclimatic seasons. A higher isotopic niche overlap was observed between size classes 2 and 3 during the dry season. The rocky shore ecosystem has been heavily exploited by artisanal fisheries (fish and invertebrates). A more integrated, ecosystem-based management of these fisheries requires an understanding of their trophic structure.

The microbial contribution to the trophic position of stomiiform fishes

Abstract The trophic position (TP) of fishes determines their importance in terms of energy flows within food webs. However, accurate estimations of TP are often prevented because of the difficulties in tracing all food sources. This is particularly challenging for omnivorous fishes, such as those from the Order Stomiiformes. In this study, we applied recent developments in stable isotope analysis of amino acids to untangle the contributions of microbial vs. metazoan food webs in 13 species of Stomiiformes. The inclusion of the microbial food web reduced the differences between TP estimates using stable isotopes and those derived from stomach content analysis. In addition, the new estimates allowed to quantify the relative contribution of the microbial food web to each species (6–21%), highlighting the importance of detritus consumption even in piscivorous species (e.g. Stomias boa and Chauliodus danae). The comparison of TP estimates obtained with selected amino acids in fish muscle allowed for the detection of the microbial influence integrated at time scales relevant for net fish growth, even when trophic exchanges in the microbial food web occur at much shorter time scales. The assessment of TP considering the differential contribution of microbial and metazoan food webs challenges our current understanding of marine food webs; yet provides a new quantitative tool for the analysis of their structure and function.

Spoiled for Choice during Cold Season? Habitat Use and Potential Impacts of the Invasive Silurus glanis L. in a Deep, Large, and Oligotrophic Lake (Lake Maggiore, North Italy)

The ecological features of invasive alien species are crucial for their effective management. However, they are often lacking in newly invaded ecosystems. This is the case of the European catfish Silurus glanis L. in Lake Maggiore, where the species is present since 1990, but no scientific information is available on its ecology. To start filling this knowledge gap, 236 catfish (67 cm to 150 cm of total length) were collected, measured, and dissected for stomach content analyses from three localities and in two habitats (littoral vs. pelagic) in late autumn/early winter. The NPUE and BPUE (individuals (N) and biomass (B, in grams) per unit effort (m2), respectively) of catfish were generally higher in littoral (NPUE &gt; 0.01; BPUE &gt; 96) than in pelagic habitats (NPUE &lt; 0.009; BPUE &lt; 114), but the catfish had, on average, larger sizes in pelagic habitats. Overall, 581 individual prey items were recorded, belonging to 12 taxa. Pelagic catfish specialized their diet exclusively on three prey fish (coregonids, shad, and roach), whilst the diet of littoral catfish was more variable and dominated by crayfish, perch, and roach. These results highlighted for the first time the interaction of larger catfish with the lake’s pelagic food web, and thus possible consequences are discussed, including the potential contrasting role S. glanis may have for the lake’s fishery.

Trophic assessment and isotopic niches of the sympatric penaeids species Penaeus brasiliensis and P. paulensis in SW Atlantic estuarine systems

ABSTRACT Penaeus brasiliensis and P. paulensis are shrimp species which overlap their distribution only in the Southwest Atlantic. In addition, they are fishery resources intensively exploited. The interactions between these two sympatric species, especially sharing of food resources, are still unknown. We have investigated the niche breadth of juvenile pink shrimps in two proximal coastal nurseries (Sepetiba and Guanabara bays) located in Southeast Brazil (∼23°W) by means of stable isotopes and stomach content analyses. These two bays are important nurseries for these species and are located in one of the most populous regions of Brazil. Diets were basically composed of benthic invertebrates (mollusks, crustaceans and polychaetes), particulate organic matter and benthic diatoms. We detected significant spatial differences in isotopic compositions (δ13C and δ15N), with pink shrimps from Guanabara Bay displaying the lowest values of both isotopes. The δ13C range and diet support that benthic microalgae are the primary producers in P. brasiliensis and P. paulensis food chains. Trophic diversity was higher in Guanabara Bay based on δ15N range, Standard Ellipse Area, and Centroid Distance metrics, displaying greater individual variability in isotopic signatures compared to Sepetiba Bay, probably due to enhanced food diversity and spatial heterogeneity in the former. The overlap in the ellipses areas between the two shrimp species was greater in Sepetiba Bay and indicates a greater sharing of resources that should be more abundant and available. Niche metrics analysis revealed greater spatial rather than interspecific differences. We advocate paying particular attention to monitoring the pink shrimps of Sepetiba Bay due to their smaller trophic niche width and lower δ15N range, which increases their sensitivity to changing habitat, mainly due to human actions.

Use of diet and body condition assessments as intermediate indicators of translocation success in the Critically Endangered Philippine crocodile (Crocodylus mindorensis)

AbstractIntermediate metrics of translocation success are useful for long‐lived, slow to mature species where survival and reproduction happen over decades.With fewer than 150 individuals in the wild, the Critically Endangered Philippine crocodile (Crocodylus mindorensis) is one of the most threatened species on Earth. This study presents the first analysis of diet and body condition of wild Philippine crocodiles and headstarted (i.e. captive‐reared) individuals released into the wild over the last decade, and uses these results to show how diet and body condition can be pertinent intermediate metrics of translocation success.Analyses of stomach contents revealed 17 different aquatic and terrestrial invertebrate and vertebrate prey species. Interestingly, 70% of Philippine crocodiles showed snails to be the predominent prey type, followed by fish (36.7%), birds (33.3%) and reptiles (33.3%). More than 50% of crocodiles consumed the invasive golden apple snail, a leading agricultural pest. Regardless of crocodile history (wild vs. headstarted) or size class (juvenile vs. adult), no evidence was found for dietary differences in percentage occurrence, percentage composition or prey diversity.Body condition was significantly higher in wild compared with headstarted individuals when analysed together in a pooled group, although neither group differed significantly from the standardized expectation, and headstarted individuals were not significantly different when body condition was derived independently for the two groups.This study provides a working example of how assessing the convergence of diet and body condition between translocated and wild individuals can provide complementary monitoring parameters to demonstrate post‐release establishment of translocated crocodylians. The congruent dietary composition and comparable body condition observed in this study suggest that headstarted crocodiles adapt well following release.Crocodylus mindorensissurvives in an agricultural landscape and is likely to play an ecologically important role by exploiting invasive species, reinforcing the importance of this species to local communities.

Biological and Ecological Aspects of the Blackmouth Catshark (Galeus melastomus Rafinesque, 1810) in the Southern Tyrrhenian Sea

Data on the biology and ecology of Galeus melastomus are old/absent for the Southern Tyrrhenian Sea, despite there being numerous studies in the wider area. A total of 127 specimens of G. melastomus from the southern Tyrrhenian Sea, collected in 2018–2019 using trawling nets, were analyzed to investigate size at sexual maturity, sex ratio, length–weight relationships, and feeding habits. To our best knowledge, this is the first time in which all these features were investigated in the Southern Tyrrhenian Sea for G. melastomus. The stomach content analysis showed that G. melastomus had intermediate feeding habits, preying on a great variety of species, especially Cephalopoda, Osteichthyes, and Crustacea. The Levin’s index value (Bi) was 0.53. Sex ratio was 0.92:1, with females slightly more abundant and bigger than males. The results also showed a decrease (33.7 cm for females, 31.1 cm for males) in length at 50% maturity (L50). This could be a result of anthropogenic stressors, such as overfishing and/or and environmental changes, which can induce physiological responses in several species. Our results highlighted the differences related to sexual maturity, growth, and feeding habits of the blackmouth catshark in the studied area, providing reference data to allow comparison with future studies on this species adaptations to this and other deep-sea areas in the Mediterranean Sea.

Stomach content analysis and feeding habit of the Antarctic krill &amp;lt;italic&amp;gt;Euphausia superba&amp;lt;/italic&amp;gt;: A review

Antarctic krill (<italic>Euphausia superba</italic>) has become a key species in the Antarctic ecosystem due to its abundant biomass and important position in the food web; therefore, its ecological role and feeding activities have garnered increasing attention. Antarctic krill is a typical phytophagous zooplankton, but also exhibits a certain degree of omnivorous behavior, as its feeding composition differs owing to the varying dominance of phytoplankton in the sea, thus having the potential to be a natural sampler of phytoplankton. The study of stomach content analysis has a long history, but those studies have significant spatiotemporal differences and the study areas were sparse and uneven with regard to circumpolarly. With the application of emerging approaches in the study of feeding habits, stomach content analysis has lacked necessary attention in recent years, due to being time-consuming, labor-intensive, and requiring a high-level of professional knowledge. However, as a direct way to examine the short-term feeding activity of Antarctic krill, the limitation of this single approach could be overcome by combining the traditional method, i.e. stomach content analysis, with lipid biomarker analysis, stable isotope analysis, PCR, and other emerging methods. Such practice will provide more accurate and comprehensive data on the feeding ecology of Antarctic krill for future studies. This paper summarized and concluded the research status of the stomach contents of krill, methods and applications, major gastric species, and seasonal, sea area, and ontogenetic differences, and further explored the potential of stomach content analysis of krill as a natural sampler of phytoplankton in the Southern Ocean. The results provide new scientific ideas for further study of the trophic dynamics of the Antarctic marine ecosystem.

Microplastic ingestion by Characidae in rural streams (Rio Grande do Sul, Brazil)

Microplastics (MP) have several negative effects on biodiversity, from the ecosystem to individual levels, and can be easily consumed by small invertebrates and fish. The increased production of plastic and absence of efficient management systems for these residues facilitate their presence in aquatic environments. In this study, we evaluated the presence of MP in the stomach contents of four species of Characidae in rural streams in the upper portion of the Uruguay River watershed (northern Rio Grande do Sul). Among the total of collected organisms (n=121), the presence of MP was observed in 72% of the analyzed stomach contents. Bryconamericus iheringii had the highest occurrence of MP (85.7%), followed by Astyanax lacustris (69.4%), Astyanax henseli (69.1%) and Oligosarchus breviostris (66.7%). Our results demonstrate the high occurrence of MP in freshwater aquatic environments, especially rural streams. The results observed in this study confirm the importance of conservation of streams, from the maintenance of riparian vegetation as a way to reduce the input of MP in these ecosystems.

Bio-Ecological Features Update on Eleven Rare Cartilaginous Fish in the Central-Western Mediterranean Sea as a Contribution for Their Conservation.

Cartilaginous fish are commonly recognized as key species in marine ecosystems for their fundamental ecological role as top predators. Nevertheless, effective management plans for cartilaginous fish are still missing, due to the lack of knowledge on their abundance, distribution or even life-history. In this regard, this paper aims at providing new information on the life-history traits, such as age, maturity, reproductive period, in addition to diet characteristics of eleven rare cartilaginous fish inhabiting the Central-Western Mediterranean Sea belonging to the orders Chimaeriformes (Chimaera monstrosa), Hexanchiformes (Heptranchias perlo and Hexanchus griseus), Myliobatiformes (Aetomylaeus bovinus and Myliobatis aquila), Rajiformes (Dipturus nidarosiensis and Leucoraja circularis), Squaliformes (Centrophorus uyato, Dalatias licha and Oxynotus centrina) and Torpediniformes (Tetronarce nobiliana), useful for their assessment and for future management actions. Particularly, the present paper provides for the first time the age estimation of D. nidarosienis and L. circularis which were both found capable of becoming older than ten years. In addition, the present study updates the sizes of first maturity of C. uyato and D. licha, which appeared to be capable of reproducing earlier than what was previously hypothesized, representing very valuable information for a better understanding of these rare species populations status and, eventually, their conservation. On the basis of the stomach content analysis, it was possible to identify five different predator groups.

Assessing trophic interactions between pelagic predatory fish by gut content and stable isotopes analysis around Fernando de Noronha Archipelago (Brazil), Equatorial West Atlantic.

The objective of this study was to analyse the feeding habits and trophic interactions between four oceanic predatory fish around the Fernando de Noronha Archipelago (FNA), Brazil, in the western equatorial Atlantic (3.86°S/32.42°W), internationally recognized as an environment of high economic and ecological value. For this purpose, biological samples of yellowfin tuna (Thunnus albacares), wahoo (Acanthocybium solandri), barracuda (Sphyraena barracuda) and dolphinfish (Coryphaena hippurus) were collected for stomach content and stable isotope analysis. Values of the index of relative importance revealed varied diets, with a strong presence of teleost fishes (Diodontidae and Exocoetidae) for all species, with yellowfin tuna having a greater diversity of food items. Despite being generalists/opportunists, the feeding strategy of these predators showed a tendency towards a specialized diet in the use of the available resources around the FNA. They presented a narrow trophic niche width (Levin's index, Bi < 0.6) and low overlap between species, except between barracuda and wahoo (MacArthur and Levin's, R0 =0.72). Isotopic compositions had broad values of δ13 C and δ15 N, and were significantly different between species. Our results provide information about the four species' trophic organization and suggest that the predators avoid competition by preying on different prey, thus allowing their coexistence.

Feeding habits and seasonal trophic guilds structuring fish community in the bay mouth region of a tropical estuarine habitat.

Understanding trophic relationships of fish in estuarine ecosystem is an important element for sustainable resource management. This study examined the feeding habits of 29 dominant fish species, characterized the trophic guilds, assessed the impact of season and clarified the role of diets in structuring the fish community in the mouth region of Pattani Bay, Thailand. Samples of 5792 fishes collected monthly by gillnets from March 2019 to February 2020 were used for stomach content analyses. It was found that the number of food types and fullness index differed between fish taxa (P < 0.001). Most fishes were specialist feeders feeding on specific food components and were categorized into five trophic guilds: piscivore, shrimp-fish feeder, polychaete feeder, zooplanktivore and planktivore. Six species were piscivorous, considered as apex predators, that fed almost entirely on fishes. High diet overlaps among some species (>0.6) were recorded. Not much variation in seasonal guilds was observed: four guilds in the dry season, three in the moderate rainy season and four in the rainy season. Some species remained in the same guild the whole year round, but some fishes changed seasonally. Two fish communities from different regions of the bay were segregated based on feeding habits. The inner bay community comprised mainly copepod and plankton feeders, but there were more piscivores in the deeper bay mouth area. Results from this study help us to understand the feeding habits and trophic guilds of dominant fish species at the mouth of this tropical estuarine bay.