Insectivorous Fish Research Articles

Short Communication: Aplocheilus panchax Hamilton, 1822 Found at Acidic Waters of Abandoned Ex-tin Mining Ponds as Insectivorous Fish and Its Role for Water Quality Improvement

Kepala timah fish or blue panchax is one of the species found at acidic waters of abandoned ex-tin mining pond. Kepala timah fish belongs to the extremophile fishes which can survive in extreme aquatic environments caused by pressure from environmental factors. This study aimed to confirm the kepala timah fish as a species of Aplocheilus panchax and to analyze its natural food habits. Molecular analysis through DNA barcoding was carried out by analyzing the COI gene and confirming the sequence of kepala timah fish in the gene bank on the NCBI website and constructing a phylogenetic tree for kepala timah fish to other A. panchax populations. Analysis of food habits was carried out by identifying the contents of the digestive tract of kepala timah fish which were observed microscopically. The results showed that kepala timah fish found at acidic waters of abandoned ex-tin mining pond was confirmed as Aplocheilus panchax Hamilton, 1822. Some morphological characters confirmed the similarity between kepala timah fish and A. panchax such as a silvery white spot on its head, terminal type of the mouth position, body shape was sagittiform, small dorsal fin on posterior body, and the shape of the caudal fin was rounded or rhomboid. Analysis of the contents of digestive tract showed the food habits of A. panchax found at acidic waters of ex-tin mining pond was insects. The food habits explained that A. panchax was classified as larvivorous or insectivorous fishes. The presence of A. panchax and its metabolic activity at abandoned ex-tin mining ponds can contributed to increasing organic matter in the waters so that it can be beneficial for improving water quality.

KOMUNIKASI SINGKAT: KEBIASAAN MAKAN IKAN KEPALA TIMAH (Aplocheilus panchax, Hamilton 1822) DI PERAIRAN EKSTREM ASAM PASCATAMBANG TIMAH TERABAIKAN

Kepala Timah (Aplocheilus panchax, Hamilton 1822) is one of the fish that has the survival abilities to live in a wide variety of quality waters. The ability of A. panchax to survive in acidic waters has begun to be widely studied as extremophile fish to study ecosystems in aquatic habitats that have acidic characteristics. This study aimed to determine the food habits of A. panchax as natural food in acid water of abandoned ex-tin mining activity. The results showed that the natural food for A. panchax was insects larvae or insects that fall on the surface of the waters. The food habits and terminal mouth type confirmed that A. panchax was surface feeder fish, carnivorous fish, larvivorous or insectivorous fish. The sagittiform body type was used A. panchax to did the strategy of feeding behavior by pursue or ambush their prey and it indicated that A. panchax as ambush predator.

Compound‐specific stable isotopes resolve sources and fate of polyunsaturated fatty acids in biota of headwater streams

Abstract Organisms at the base of stream food webs are typically poor in long‐chain polyunsaturated fatty acids (LC‐PUFA), especially in docosahexaenoic acid (DHA), whereas consumers at higher trophic levels are often rich in LC‐PUFA. For example, fish tissues, especially the brain, are DHA‐rich. This obvious mismatch between consumer LC‐PUFA and their basal dietary supply may result from selective retention and/or endogenous conversion of dietary precursors to LC‐PUFA. To determine which is more likely, we investigated compound‐specific carbon stable isotopes in PUFA (δ13CPUFA) of potential basal resources (stream epilithon, leaf litter) and consumers (invertebrates, European bullhead, and two salmonid species and their brain, eye, liver, and muscle tissues). We predicted that consumer‐PUFA, depleted in 13C values relative to their dietary sources, would indicate internal de novo PUFA synthesis. Alternatively, higher consumer‐δ13CPUFA values would imply selective retention of aquatic (epilithon and conditioned leaves) rather than terrestrial resources or internal production, irrespective of trophic levels. Invertebrate grazers and predators resembled δ13C values of essential fatty acids (δ13CEFA) of benthic algae, while shredder‐δ13CEFA values reflected those of conditioned rather than fresh leaves. Lower eye‐δ13CEFA values of salmonids than in livers indicated high retention of dietary PUFA sources (invertebrates and epilithon). Stable isotope values of eicosapentaenoic acid suggest that all consumers retained algal EPA, while insectivorous fish produced DHA in their liver. There is no further evidence from carbon stable isotopes for local PUFA conversion within neural tissues. Our study demonstrates that δ13CPUFA can be used to track sources of these highly functional molecules in aquatic consumers and highlights the importance of algal derived‐PUFA for these consumers in oligotrophic headwater streams.

Indirect functional effects of neighbors on food web compartments could not overcome density-dependent limited growth of a grazing minnow

Ecosystems include diverse taxonomic and functional groups of animals with variable levels of niche overlap that can lead to direct and indirect interactions with positive or negative outcomes. Species feeding at low trophic positions might be sensitive to interactions with co-occurring functional groups (neighbors) that influence their food resources through various processes, such as indirect nutrient subsidies and trophic cascades. Employing a target-neighbor experimental design using large, outdoor mesocosms, we tested whether adding neighbors with different functional traits affected food web compartments relative to a control group that had grazing minnows, Campostoma anomalum (Central Stoneroller). Additionally, we tested whether growth and body condition of Central Stoneroller was positively influenced through interactions with each neighbor treatment: additional stonerollers, benthic-insectivorous fish Etheostoma spectabile (Orangethroat Darter), terrestrial insectivorous fish Lepomis megalotis (Longear Sunfish), or filter-feeding mussels (two-species assemblage) that are predicted to increase primary production through nutrient enrichment, a trophic cascade or both. Over the 29-day experiment, the presence of neighbors had generally negative or highly variable effects on food web compartments. Stoneroller growth was not evident during the experiment and body condition generally declined but was not influenced by neighbor treatments. Our results show that adding neighboring functional group did not reduce density-dependent growth of grazing fishes via indirect food web interactions over short temporal scales. This study suggested that indirect interactions among species and their combined influence on ecosystem properties were weak under experimental conditions representing typical prairie stream communities.

Microplastics in fishes in amazon riverine beaches: Influence of feeding mode and distance to urban settlements

Microplastic (MP) pollution is a global problem and has affected several biological levels even in protected areas. In the present study, MP contamination was investigated in fish associated with sandy beaches in a permanent environmental protection area in the Amazon. In order to achieve this goal, the shape, color, abundance, richness, and chemical composition of MPs in the digestive tract of 29 fish species in 24 beaches of the Machado River, western Brazilian Amazon, were evaluated. Linear mixed models (LMMs) were adjusted to test the effects of local human modification (HMc), distance from urban settlements, distance from the closest affluent, and trophic categories of fish species on microplastic abundance and richness in their digestive tracts. From the 1082 fish analyzed, 332 (30 %) presented MPs in their digestive tracts. A total of 617 MPs was found (1.8 ± 1.6 MPs; 4.5 ± 1.9 MPs/g fish). Omnivorous and insectivorous fish presented more MPs in sandy beaches located closer to urban settlements. However, carnivorous fish presented a higher abundance of MPs in their digestive tracts compared with the other trophic guilds. This is the first study to analyze plastic contamination in fish associated with sandy beaches in the Amazon (Brazil), and it revealed contamination of the ichthyofauna mainly related to the distance from urban settlements. Our results reinforce the need for better management of landscape surrounding protected areas to mitigate MP pollution.

Season and environment modulate aquatic invertebrates’ responses to trout and indigenous fishes in three South African mountain streams

Introduced organisms are seen as one of the greatest threats to resource sustainability worldwide, and aquatic macroinvertebrates are regarded as good indicators of the health of water resources. To explore these two perspectives, the responses of macroinvertebrate faunas to native and introduced fishes in three headwater tributaries of the Keiskamma River system, South Africa, were examined by comparing potential indicator communities in reaches considered to be fishless, reaches invaded by introduced salmonid species, and reaches containing native fishes. Patterns in the macroinvertebrate faunal assemblage data were driven strongly by season and flow rate, and less strongly by the presence of insectivorous fishes and biotope availability, a finding in parallel with several similar studies from the region. This affirms that aquatic macroinvertebrate faunas are responsive indicators of both environmental and biotic factors and leaves room for further studies to resolve the effects of non-native fish in the Keiskamma River system and other similar systems from South Africa.

Exploring fish assemblage structure, feeding guild, and water quality in a typical river-reservoir interface of tropical large reservoir environment, Central India.

The present study aims to understand the spatio-temporal dynamics in habitat ecology and fish assemblage and determine the relationship of habitat transition and fish distribution in a large riverine-reservoir cascade system (Sardar Sarovar Reservoir part in Madhya Pradesh). This study was carried out along a 125-km riverine-reservoir interface (RRI) during 2018-2020. The study showed presence of a total of 110 fish species (104 spp. in upstream main Narmada River stretch excluding reservoirs, 56 in RRI, and 39 in Sardar Sarovar reservoir). We recorded 50 species common in upstream riverine stretch of Narmada and the RRI while RRI uniquely harbored 3 native species (Chitala chitala, Labeo boga, Salmostoma phulo) not previously reported from Narmada River stretch upstream. The similarity percentage (SIMPER) analysis showed presence of S. phulo causing 27.91%, Schistura dayi (3.71%), and Rita pavimentata (3.41%) of dissimilarity among Maheshwar (S1), Rajghat (S2), Koteshwar (S3) non-confluence zone, and Kakrana (S4)-confluence zone. The analysis of data indicated disappearance of some species like deccan peninsular carp Labeo fimbriatus, Mahseer Tor khudree which was earlier reported but was absent in recent years. The statistical correlation of environmental variables with observed abundances offish feeding guilds showed significant positive correlation with specific conductivity and total dissolved solid content of the water. The canonical correspondence analysis (CCA) indicated association among omnivorous fishes of the reservoir with water temperature; total dissolved solids; specific conductivity; total alkalinity; chlorophyll; and NO3-N. The herbivore fishes were found to be more associated with magnesium, dissolved oxygen, and phosphorus content of the water while insectivorous fishes were more associated with the silicate and transparency of the water. The abundance of omnivores species indicated dominance of generalist fish species rather than specialists in the interface region of reservoir showing conservation and ecological importance of the ecosystem. The baseline information generated on fish assemblage and ecological perspectives of the river reservoir interface and science-based management recommendations formulated in the study are critical for sustaining fish diversity, promoting fisheries enhancement, and management planning of tropical large reservoirs.

Export and bioaccumulation of methylmercury in streams draining distinct soils in the Central Brazilian Amazon, 2012-2013

BackgroundUpland forest streams of the Central Amazon are unique aquatic systems.These small streams have short, unpredictable and multimodal flood-pulses that are influenced by local rainfall. The biogeochemical cycles in these systems are almost unknown. This study investigated the role of soil type on the export and bioaccumulation of methylmercury (MeHg) in upland forest streams of the Central Amazon during a complete annual cycle. Basic ProceduresLimnological measurements and water samples for MeHg analyses were collected monthly from October 2012 to October 2013 in two headwater streams drained by different soil types, spodzol (Campina Stream) and oxisol (Barro Branco Stream), in natural forest reserves. Shrimp and fish were collected for total mercury (THg) in April 2013 in both streams. Main findingsMeHg in water varied from 0.04 to 0.50 ng/L in the Campina Stream and between <detection limit and 0.04 ng/L in Barro Branco Stream. Physical characteristics of soils and the interaction between mercury and organic matter influenced the methylation of mercury and its export to the streams. In both streams, MeHg export was highest during the rainy season, probably due to soil leaching, lateral flooding and soil hydromorphism during this period, processes conducive to mercury methylation and export. THg in shrimps (omnivores) and carnivorous fish, which fed on aquatic food items, reflected the MeHg differences between streams while those in insectivorous fish, feeding on allochthonous food items, did not. Principal ConclusionsMeHg dynamics in streams were influenced by the physical characteristics of basin soils and by local seasonal rainfall.

Relationships between land use, habitat quality, physicochemical water quality and fish communities in the Sironko River Catchment, a mountainous tropical stream flowing into the Lake Kyoga in Eastern Uganda

AbstractThis study investigated the relationships between land use, habitat quality, physicochemical water quality and fish assemblage in the Sironko River catchment, a tropical mountain stream flowing into the Lake Kyoga asin in Eastern Uganda. The study was carried out at different land use sampling sites (natural forest, pastureland, plantation forest, mixed agriculture, banana plantation, urban and sugarcane plantation) for 6 months from November 2019 to April 2020. The habitat quality score (HQS) ranged between 49% in the urban area and 75% in the natural forest. There was a general increase in the temperature, conductivity, total dissolved solids, turbidity and nitrate concentration in the Sironko River as it flowed from upstream to downstream from the natural forest to the sugarcane plantation. Conversely, there was a reduced dissolved oxygen concentration and water transparency as the river traversed the different land uses downstream. A total of 765 fish individuals belonging to 9 fish species (Amphilius jacksonii, Amphilius uranoscopus, Barbus altianalis, Labeo victorianus, Clarias leocephalus, Clarias carsonii, Cyprinus carpio, Barbus palludinosus and Barbus jacksonii) were captured using an electrofishing gear. Fish identification was based on external morphological characteristics. Amphilius uranoscopus and Barbus altianalis were only caught in the natural forest and pastureland at a high altitude characterized by low temperature and high dissolved oxygen concentration. The fish species belonged to 3 trophic feeding groups dominated by the insectivorous fish. Pearson correlation coefficients showed a weak negative relationship (r = −0.249) between fish community and habitat quality, while fish assemblage and physicochemical water quality unveiled a weak positive relationship (r = 0.176). The coefficient of determination (R2 = 0.695) indicated 69.5% of the fish community variability was accounted for by the physicochemical water quality variables in Sironko River System. Accordingly, it was concluded that physicochemical water quality attributes are the most important factors determining the distribution of fish species with land use in the Sironko River catchment, a tropical mountain stream. The Sironko River catchment is hydraulically and biologically connected to Lake Kyoga through a series of satellite lakes and swamps. The river is spawning area for Clarias leocephalus, Clarias carsonii and Amphilius lujani fish species of the lake.

Trophic Patterns of Freshwater Fish across the Balkan Biodiversity Hotspot

Ecological information regarding trophic patterns and the inherent structure of freshwater aquatic communities is considered fundamental in ecological research. In this study, the trophic patterns of the Greek freshwater fish fauna, belonging to the Balkan biodiversity hotspot, were investigated, and comparisons of freshwater fish species feeding habits among the Greek freshwater ecoregions were performed. The analyses based on the widely used trophic level index and the available composition feeding datasets, along with the utilization of clustering methods, indicated seven major distinct trophic guilds in the Greek ecoregions. The trophic level of the studied fish species ranged from 2.0 to 4.5, thus being within the expected values for freshwater ecosystems, revealing the presence of both top predators and primary consumers. The highest trophic level values were found in the ecoregions of northern Greece. The results also exhibited considerable predominance of higher-trophic-level zooplanktivorous and insectivorous freshwater fish species in the mainland, compared to lower-trophic-level opportunist species in the island-isolated ecoregions. These results could be used for the application of ecosystem-based models and the formulation of conservation and fishery management schemes.

Occurrence and characteristics of microplastics in fish of the Han River, South Korea: Factors affecting microplastic abundance in fish

This study examined the abundance of microplastics (MPs) in 106 fish from 22 species inhabiting three sites of the Han River, South Korea. In total, 1753 MPs from 106 fish samples were identified with an average abundance of 15.60 ± 13.45 MPs per individual fish (MPs indiv−1) in the North Han River, 16.35 ± 12.32 MPs indiv−1 in the South Han River, and 20.14 ± 10.01 MPs indiv−1 in downstream of the Han River, indicating that the fish in the downstream of the Han River was the most contaminated by MPs. The dominant size of MPs detected in fish ranged between 0.1 and 0.2 mm, and the most common polymer types found in fish were polypropylene (PP) (≥40%) and polyethylene (PE) (≥23%), followed by polytetrafluoroethylene (PTFE) (≥16%) at all sampling locations. A significant correlation was observed between the log-transformed number of MPs with log-transformed fish length (p < 0.01) and with log-transformed fish weight (p < 0.01). The Kruskal-Wallis test disclosed a significant difference in the number of MPs among the feeding habits (p < 0.01), indicating that omnivorous and insectivorous fish contained more MPs than carnivorous and herbivorous fish. In addition, fish habitat result showed that pelagic fish contained a higher level of MPs than demersal fish, but no significant differences in the number of MPs among fish habitats were observed (p > 0.05).

Impacts of environmental factors on the food web structure, energy flows, and system attributes along a subtropical urban river in southern China

Tropical and subtropical rivers are being subjected to multiple stressors from human disturbance (e.g., water pollution and habitat degradation). Understanding the relationship between environmental conditions and the river ecosystem is important for improving river management. We built 14 Ecopath models composed of 28 functional groups (trophic levels [TLs] of 1.0–3.8) along a subtropical urban river to explore the influence of environmental changes on system attributes. From headwaters to downstream, the model outputs showed that the transfer efficiency (TE), energy flow parameters, and ecosystem theory indices exhibited significant (P < 0.05) differences across a longitudinal gradient of disturbance, indicating heterogeneous attributes of local river segments. The high TE values of TLs I, II, and III separated the upper, middle, and lower reaches, respectively, which could be attributed to the shift in dominant consumption flows from upstream ‘periphyton – aquatic insects – insectivorous fish’ to midstream ‘detritus – shrimp – crustaceavorous fish’ and to downstream ‘phytoplankton – filter-feeding invertebrates/fish’. Structural equation modelling was used to test the causal relationships among environmental variables and demonstrated that abiotic factors directly influenced biomass composition and indirectly influenced trophic networks. Water quality, including dissolved oxygen and flow velocity; habitat characteristics, such as riffles, cobble-gravel substrate, and seasonal floodplain; and biological indicators, including the relative contributions (%) of decapods, insectivorous fish, and insect scrapers to biomass composition, had significant (P < 0.05) positive impacts on system maturity (evaluated by omnivory, connectance, and cycling indices). In the future, it will be possible to evaluate the health of river ecosystems by monitoring representative environmental factors, which could be a cost-effective approach to system-level improvement.

Pervasive decline of subtropical aquatic insects over 20 years driven by water transparency, non-native fish and stoichiometric imbalance.

Insect abundance and diversity are declining worldwide. Although recent research found freshwater insect populations to be increasing in some regions, there is a critical lack of data from tropical and subtropical regions. Here, we examine a 20-year monitoring dataset of freshwater insects from a subtropical floodplain comprising a diverse suite of rivers, shallow lakes, channels and backwaters. We found a pervasive decline in abundance of all major insect orders (Odonata, Ephemeroptera, Trichoptera, Megaloptera, Coleoptera, Hemiptera and Diptera) and families, regardless of their functional role or body size. Similarly, Chironomidae species richness decreased over the same time period. The main drivers of this pervasive insect decline were increased concurrent invasions of non-native insectivorous fish, water transparency and changes to water stoichiometry (i.e. N : P ratios) over time. All these drivers represent human impacts caused by reservoir construction. This work sheds light on the importance of long-term studies for a deeper understanding of human-induced impacts on aquatic insects. We highlight that extended anthropogenic impact monitoring and mitigation actions are pivotal in maintaining freshwater ecosystem integrity.

Fish feeding groups, food selectivity, and diet shifts associated with environmental factors and prey availability along a large subtropical river, China

Understanding spatial variation in fish trophic structures along large river systems remains a challenge, and the influence of fish food selectivity and diet shifts on these structures remains unknown. In this study, the assemblage composition and stomach contents of fish in the subtropical East River of southern China were analyzed to determine their diet composition (DC) and identify prey-oriented feeding groups. Ten prey items were identified and used to cluster 106 fish species into 23 feeding groups. The number of groups increased longitudinally due to the accumulated emergence of site-specific prey sources in fish DC, although this number decreased sharply near the estuary due to the loss of insectivorous fish. The fish assemblages showed a longitudinal decrease in abundance and an increase in biomass, with higher values observed in the rainy season than the dry season. A downstream decrease in insectivores and epiphytivores and increase in detritivores and molluscivores represented the basic patterns observed along the river. Seven widespread fish species exhibited spatial dietary shifts, among which three generalist feeders with a high abundance notably influenced the fish trophic structures, and four specialist feeders with high food selectivity were significantly (P < 0.05) correlated with prey availability. Multivariate data analysis showed that the flow velocity, water depth, riffle areas, and nutrient concentrations were the key environmental factors that determined the distribution of fish feeding groups, while hydrophytes, plant debris, Ephemeroptera and Odonata insects, and Atyidae shrimp were the key prey sources.

Diet of two insectivorous fish species in a Brazilian semiarid reservoir

Long periods of aridity can cause changes in the diet of fish since hydrological variations affect the availability of food resources. The objective of this study was to investigate the diet of two species of fish (Astyanax aff. bimaculatus and Triportheus signatus), present in the Umari reservoir in Upanema, Rio Grande do Norte, Brazil, to evaluate the influence of seasonality on their diets. The samples were collected quarterly during the months of February to November 2013, with four days in the field, and at five different sites of the reservoir with nets with meshes ranging from 12 to 70 mm (between adjacent nodes). For the identified items in the diet, the frequencies of occurrence and volume, combined in the calculation of the Alimentary Index (IAi), were obtained. Significant alterations in the diet of the species were observed, predominantly in insects. The changes found in the diet indicate an influence of seasonality on the feeding habits of these species, with a predominance of autochthonous items in the dry period and allochthonous items in the rainy period.

Longitudinal variation in energy flow networks along a large subtropical river, China

To understand the longitudinal variation in the structure and functioning of large river ecosystems, six Ecopath models were constructed to exhibit the energy flows of aquatic food webs along the subtropical East River in China. Input parameters were primarily obtained from field data collected in 2012–2016; model outputs were estimated by network analysis. Longitudinally, ecosystem characteristics of the East River had high spatial heterogeneity. The biomass, production, and consumption, of which >75.8% of each was distributed at trophic level (TL) II, were determined by aquatic insects upstream, molluscs midstream, and zooplankton downstream. Carnivorous fish occupied the maximal TL of 2.95–3.50. Due to the different trophic interactions of regional food webs, the keystone groups shifted from odonate larvae in headwaters to piscivorous fish upstream/midstream, to zooplankton downstream, and to phytoplankton near the estuary. Aquatic insects, insectivorous fish, epiphytes, and hydrophytes, all of which had ecotrophic efficiencies >0.99, were critical groups that influenced mass balance through short prey supply. The mean transfer efficiencies (TEs) through TLs IIIV had the lowest values of 1.8–4.1% upstream and increased to the highest levels of 8.0–8.4% midstream before they decreased to 6.4–7.0% downstream. The low TEs along the river were limited mainly by the lack of carnivorous fish upstream and the low predation on mollus and plankton midstream/downstream. A series of theory and information indices showed that the pristine upstream system was mature but underdeveloped in organisation; in contrast, the downstream systems in the urban and industrial reaches were immature and stressed in terms of excessive phytoplankton production and short cycling.

The river continuum concept predicts prey assemblage structure for an insectivorous fish along a temperate riverscape

AbstractThe river continuum concept (RCC) provides a framework for processes structuring lotic ecosystems by synthesizing sources and transport of C in streams. Considerable attention, refinement, ...

Gut content biomass of stream fishes: associations with streamflow velocity, population density, and prey abundance at two spatial scales

Although food consumption rate has been identified as an important biological variable informing growth rates and population dynamics in fisheries management, equivalent measures receive little attention for native stream fishes. This research investigates whether spatial variation in fish gut fullness can be explained by streamflow velocity, population density, or prey abundance. We tested hypotheses associated with outcomes of habitat-specific energetic demands, exploitation competition, and resource-driven habitat use. Gut content biomass (GCB) of insectivorous fish species was compared at reach and at landscape scales in the Meramec River basin (Missouri, USA). Explanatory variables were selected using ridge regression with cross-validation. GCB of widely distributed species was correlated with body size, streamflow velocity, conspecific fish density, and prey abundance. At the reach scale, GCB was positively correlated with streamflow velocity in three species, supporting a prediction of an optimal foraging model. Negative relationships between GCB and density of Luxilus zonatus may be due to exploitation competition, while positive relationships between GCB and density of Etheostoma flabellare likely result from resource-driven habitat use. We found few relationships between GCB and explanatory variables at the landscape scale, suggesting that unmeasured biological and habitat variables are more important determining gut fullness at broad spatial scales.

Trophic structure of coastal freshwater stream fishes from an Atlantic rainforest: evidence of the importance of protected and forest-covered areas to fish diet

The role of riparian forests in the functioning of aquatic ecosystems is well known, and they are recognized as an important food source for riverine fauna. This study investigates the trophic structure of coastal freshwater stream fishes from a large conservation area in an Atlantic rainforest using stomach content and food availability analyses. Four samples were collected from 19 sample sites. Fishes were caught with electrofishing. Prey were sampled with trays, Surber, traps, and electrofishing to evaluate the availability of food resources. The diets of 20 fish species were determined from the stomach contents of 1691 individuals. Terrestrial and aquatic insects and detritus were the most consumed items. Fish diet and prey availability were not seasonally dependent. A cluster analysis showed five trophic functional groups: terrestrial insectivores, aquatic insectivores, detritivores, carnivores, and omnivores. Insectivores predominated in species richness (60%), abundance (47%) and biomass (39%). Allochthonous and autochthonous items were found in similar proportions in the environment; however, allochthonous items were representative for insectivores and detritivores, whereas autochthonous items were important for primarily aquatic insectivores. The preference for certain insects by insectivorous fishes was associated with food selectivity rather than the availability of the resource and demonstrated the strong relationship between feeding behavior and food preference. The absence of seasonal variation in the diets of the fishes was possibly related to the consistent food supply. Our results confirm the role of the forest as a food provider for stream fishes, such as terrestrial insects and plant debris/detritus (also consumed by aquatic insects, which subsequently serve as food for fish), highlighting the importance of conserving the Brazilian Atlantic rainforests.

Dieta y reproducción de Bryconamericus caucanus (Characiformes: Characidae) en la Quebrada La Venada, Río Quindío, Colombia

Objetivo. Se analizó la ecología trófica y reproductiva de Bryconamericus caucanus en la quebrada la Venada, Rio Quindío, Alto Cauca, Colombia. Materiales y métodos. Los ejemplares se recolectaron entre enero y diciembre del 2013. Se realizaron análisis multivariados para comparar las características tróficas entre épocas climáticas (bajas y altas lluvias), sexos y estados de madurez (juveniles y adultos). Se analizó también el factor de condición (K), porcentajes numéricos (%N), volumétricos (%V) y frecuencia de ocurrencia (%Fo) para cada presa. La proporción de sexos se evaluó usando pruebas de Chi-Cuadrado y se estimaron los indices gonadosomático (IGS) y de fecundidad absoluta (Fa). Resultados. Se analizó un total de 162 ejemplares (LS: 40-75 mm). Se encontró que B. caucanus es un pez insectívoro (86.47% IRI), con un consumo preponderante de ephemeropteros (Baetidae; 27.71%), hymenopteros (Formicidae; 23.57%), dipteros (Simuliidae 17.36%; Chironomidae 9.79%) y trichopteros (Hydropsychidae; 8.04). Los analisis multivariados revelaron diferencias tróficas entre épocas climáticas, con menor riqueza durante la época de sequía. Entre sexos, las hembras registran una mayor amplitud del nicho trófico. Los adultos, presentan una amplitud de nicho mayor a juveniles. La especie tiene dos eventos reproductivos en los periodos de altas lluvias relacionados con el incremento en la riqueza trófica durante las mismas épocas (i.e. marzo-abril, septiembre-noviembre). Conclusiones. B. caucanus presenta una segregación trófica incipiente entre estadios ontogénicos y sexos. La distinción trófica es sin embargo notable entre periodos climáticos. Los periodos de desove para B. caucanus ocurren a inicio de los periodos de lluvias (i.e. mayo-junio y septiembre-octubre).