Climate change affects the distribution of diversity across marine food webs.

Many studies predict shifts in species distributions and community size composition in response to climate change, yet few have demonstrated how these changes will be distributed across marine food webs. We use Bayesian Additive Regression Trees to model how climate change will affect the habitat suitability of marine fish species across a range of body sizes and belonging to different feeding guilds, each with different habitat and feeding requirements in the northeast Atlantic shelf seas. Contrasting effects of climate change are predicted for feeding guilds, with spatially extensive decreases in the species richness of consumers lower in the food web (planktivores) but increases for those higher up (piscivores). Changing spatial patterns in predator-prey mass ratios and fish species size composition are also predicted for feeding guilds and across the fish assemblage. In combination, these changes could influence nutrient uptake and transformation, transfer efficiency and food web stability, and thus profoundly alter ecosystem structure and functioning.

A comparison of digestive strategies for fishes with different feeding habits: Digestive enzyme activities, intestinal morphology, and gut microbiota.

Fish feeding habit determines the digestive tract structure and intestinal microflora. However, the relationship between feeding habit, digestive intestinal morphology, and microbial diversity of omnivorous, herbivorous, plankton feeder, and carnivorous fish from the same environment has not been compared. This study compared the digestive enzyme activities, intestinal morphology, and intestinal microflora of omnivorous (Carassius auratus), herbivorous (Ctenopharyngodon idellus), carnivorous (Siniperca chuatsi), and plankton feeder (Schizothorax grahami) fishes and predicted the potential functions of specific microflora on different nutrients. Twelve intestine samples were collected from each of the four fishes from Dianchi Lake. The composition and diversity of microbial communities were determined by using high-throughput sequencing of 16S rDNA. The results showed that the carnivorous fish (S. chuatsi) had higher trypsin and pancrelipase activities in the hepatopancreas and enteropeptidase in the intestine, but lower amylase activities in the intestine. The carnivorous fish intestine had more microvilli branches and complex structures than other fish species in the order carnivorous > herbivorous > plankton feeder > omnivorous. The intestinal microflora diversity was higher in the omnivorous fish and followed the order omnivorous > herbivorous > plankton feeder > carnivorous. Acinetobacter species and Bacteroides species were the most dominant flora in the carnivorous and herbivorous fishes, respectively. Acinetobacter species and Pseudomonas species might help the host to digest protein, while Bacteroidetes species may help the host to digest cellulose. Taken together, feeding habit determines the digestive enzyme activities, intestinal tissue morphology, and differential colonization of fish intestinal flora. The knowledge obtained is useful in feed formulation and feeding practices for the studied fish species.

Hydrodynamic analysis of bioinspired vortical cross-step filtration by computational modelling.

Research on the suspension-feeding apparatus of fishes has led recently to the identification of novel filtration mechanisms involving vortices. Structures inside fish mouths form a series of 'backward-facing steps' by protruding medially into the mouth cavity. In paddlefish and basking shark mouths, porous gill rakers lie inside 'slots' between the protruding branchial arches. Vortical flows inside the slots of physical models have been shown to be important for the filtration process, but the complex flow patterns have not been visualised fully. Here we resolve the three-dimensional hydrodynamics by computational fluid dynamics simulation of a simplified mouth cavity including realistic flow dynamics at the porous layer. We developed and validated a modelling protocol in ANSYS Fluent software that combines a porous media model and permeability direction vector mapping. We found that vortex shape and confinement to the medial side of the gill rakers result from flow resistance by the porous gill raker surfaces. Anteriorly directed vortical flow shears the porous layer in the centre of slots. Flow patterns also indicate that slot entrances should remain unblocked, except for the posterior-most slot. This new modelling approach will enable future design exploration of fish-inspired filters.

Novel field observations of coral reef fishes feeding on epiphytic and epizoic organisms associated with the allelopathic seaweed Galaxaura divaricata.

In degraded coral reef ecosystems, allelopathic macroalgae have received increasing attention from marine ecologists because their secondary metabolites (also known as allelochemicals) kill corals that grow adjacent to them and weaken the recovery of degraded reefs. One well-known coral-killing macroalga is the calcareous red seaweed Galaxaura. However, our knowledge of how coral reef fishes interact with allelopathic algae like Galaxaura is very limited. Here, we documented novel observations of feeding interactions of 17 species of coral reef fishes (herbivorous and carnivorous) with the filamentous Galaxaura divaricata on degraded lagoon patch reefs in Dongsha Atoll (South China Sea). Video analyses showed that territorial farming damselfishes (i.e., Dischistodus perspicillatus, D. prosopotaenia, Hemiglyphidodon plagiometopon, Pomacentrus grammorhynchus, P. adelus, and Neoglyphidodon nigroris) and juvenile parrotfishes (Scarus schlegeli, S. ghobban, S. rivulatus, and Chlorurus spilurus) likely used G. divaricata as a feeding substratum. Further, microscopic analyses revealed that the filamentous surface of G. divaricata harbored a wealth of epiphytic microalgae, such as filamentous cyanobacteria (i.e., Leptolyngbya, Lyngbya, Rivularia, Oscillatoria, and Stigonema), diatoms (i.e., Synedra, Nitzschia, Mastogloia, and Pleurosigma), and filamentous red algae (i.e., Heterosiphonia), suggesting that these fishes targeted the nutrient-rich microscopic epiphytes rather than the nutrient-poor host. Juvenile benthic carnivores (i.e., Labridae, Parupeneus multifasciatus, and Meiacanthus grammistes) form feeding assemblages with roving parrotfishes to feed on small invertebrates (i.e., amphipods, copepods, isopods, gastropods, and polychaetes) associated with G. divaricata. Given that coral reef fishes appear to target the epiphytes associated with Galaxaura rather than the alga itself, these observations thus substantiate the threat posed by the overgrowth of G. divaricata to coral recovery in degraded reef systems due to the lack of natural grazers.

Labelling fish diets with 15 N -Leucine for monitoring feed consumption and bio-distribution in Atlantic salmon.

Feeding represents 50-70% of the cost of production in salmon farming, higher than any other animal farm. The improvement of this percentage is challenging as the food is thrown into the fish tank, there is no quantification of the amount of food that is consumed by the fish. In consequence, it is difficult to adjust the food composition making it more nutritive or promoting food consumption by fish. In this study, to investigate food consumption, bio-distribution and food residues, leucine containing 15 N (a stable isotope of nitrogen) was used to label the fish food. Atlantic salmon (Salmo salar) weighing 100-120 g were maintained in 30 L tanks at a density of 14 kg/m3 . Fishes were fed daily at 1% of the fish weight with pellet labelled with 15 N-leucine. The 15 N incorporation was determined 14 hours after the feeding in all the fish organs. Results showed that 14 hours after the administration of a single dose of labelled food to Atlantic salmon enables the detection of the tracer in the whole organism allowing determining the food consumption. Through the analysis of nitrogen use efficiency (NUE), we showed that the trunk, pyloric caeca and head incorporate the highest level of the marker (72.7, 8.7 and 5.7%, respectively). This methodology would permit monitoring feeding to minimize food loss, improve administration methodologies or select the preferred foods for the fish, among others to reduce production costs.

Microplastics in some fish species and their environs in Eastern Visayas, Philippines.

Microplastics are a global concern, and yet, Philippine studies about it are still wanting. This study investigated microplastic ingestion among detritus-feeding mullet versus the herbivorous rabbitfish, and between freshwater and marine fishes. The first part aimed to compare microplastics in fishes' guts differing in feeding guilds, individual sizes, and body weights. The second part compared MPs in fishes' guts and their surrounding waters. Part one revealed that herbivores (58.57%) ingested more MPs than their detritivore-counterparts (30.0%). Pearson correlation, averaging 0.06, suggests a weak correlation between fish weight and MPs amount for both species. Part two showed marine fishes (66.0%) ingested more MPs than its freshwater counterparts (45.0%). A very weak correlation was observed between fish weight and amount of MPs ingested. Fish along the estuary ingested more MPs than those in other stations. No significant differences (p = 0.23) between the MPs in the water samples from each sampling stations was found.

Work that body: fin and body movements determine herbivore feeding performance within the natural reef environment.

Herbivorous fishes form a keystone component of reef ecosystems, yet the functional mechanisms underlying their feeding performance are poorly understood. In water, gravity is counter-balanced by buoyancy, hence fish are recoiled backwards after every bite they take from the substrate. To overcome this recoil and maintain contact with the algae covered substrate, fish need to generate thrust while feeding. However, the locomotory performance of reef herbivores in the context of feeding has hitherto been ignored. We used a three-dimensional high-speed video system to track mouth and body kinematics during in situ feeding strikes of fishes in the genus Zebrasoma, while synchronously recording the forces exerted on the substrate. These herbivores committed stereotypic and coordinated body and fin movements when feeding off the substrate and these movements determined algal biomass removed. Specifically, the speed of rapidly backing away from the substrate was associated with the magnitude of the pull force and the biomass of algae removed from the substrate per feeding bout. Our new framework for measuring biting performance in situ demonstrates that coordinated movements of the body and fins play a crucial role in herbivore foraging performance and may explain major axes of body and fin shape diversification across reef herbivore guilds.

Oropharyngeal morphology related to filtration mechanisms in suspension-feeding American shad (Clupeidae).

To assess potential filtration mechanisms, scanning electron microscopy was used in a comprehensive quantification and analysis of the morphology and surface ultrastructure for all five branchial arches in the ram suspension-feeding fish, American shad (Alosa sapidissima, Clupeidae). The orientation of the branchial arches and the location of mucus cells on the gill rakers were more consistent with mechanisms of crossflow filtration and cross-step filtration rather than conventional dead-end sieving. The long, thin gill rakers could lead to a large area for the exit of water from the oropharyngeal cavity during suspension feeding (high fluid exit ratio). The substantial elongation of gill rakers along the dorsal-ventral axis formed d-type ribs with a groove aspect ratio of 0.5 and a Reynolds number of approximately 500, consistent with the potential operation of cross-step filtration. Mucus cell abundance differed significantly along the length of the raker and the height of the raker. The mucus cell abundance data and the observed sloughing of denticles along the gill raker margins closest to the interior of the oropharyngeal cavity suggest that gill raker growth may occur primarily at the raker tips, the denticle bases, and the internal raker margins along the length of the raker. These findings will be applied in ongoing experiments with 3D-printed physical models of fish oral cavities in flow tanks, and in future ecological studies on the diet and nutrition of suspension-feeding fishes.

Quality improvement of common carp (Cyprinus carpio L.) meat fortified with n-3 PUFA.

The effect of carp feeding with n-3 PUFA-enriched feed (Schizochytrium sp. meal or salmon oil) on nutritional quality indicators (proximal composition, fatty acid profile of fat) and culinary quality (color parameters, texture, sensory properties) was evaluated. Highly significant effects of carp nutrition on chemical composition and fat characteristics, L* and a* color parameters, muscle fiber size, endomysium thickness, moisture and taste of fillets were determined. Fillets obtained from carps fed with the experimental feed contained less protein and more crude fat and had larger muscle fibers, but scored more highly in the sensory evaluation of moisture and fishy taste. In the fat of carp fed the enriched feed, a greater share of total PUFA, n-3 PUFA, total EPA and DHA, n-3/n-6 ratio, and a smaller share of total MUFA were observed compared with control fish. However, no effect of nutrition on the texture of carp fillets, assessed either instrumentally or using sensory methods, was found. The use of Schizochytrium sp. meal as a source of EPA and DHA gave much better results than salmon oil, as it allowed a higher content of these valuable fatty acids to be achieved, without compromising quality.

Predator-informed looming stimulus experiments reveal how large filter feeding whales capture highly maneuverable forage fish.

The unique engulfment filtration strategy of microphagous rorqual whales has evolved relatively recently (<5 Ma) and exploits extreme predator/prey size ratios to overcome the maneuverability advantages of swarms of small prey, such as krill. Forage fish, in contrast, have been engaged in evolutionary arms races with their predators for more than 100 million years and have performance capabilities that suggest they should easily evade whale-sized predators, yet they are regularly hunted by some species of rorqual whales. To explore this phenomenon, we determined, in a laboratory setting, when individual anchovies initiated escape from virtually approaching whales, then used these results along with in situ humpback whale attack data to model how predator speed and engulfment timing affected capture rates. Anchovies were found to respond to approaching visual looming stimuli at expansion rates that give ample chance to escape from a sea lion-sized predator, but humpback whales could capture as much as 30-60% of a school at once because the increase in their apparent (visual) size does not cross their prey's response threshold until after rapid jaw expansion. Humpback whales are, thus, incentivized to delay engulfment until they are very close to a prey school, even if this results in higher hydrodynamic drag. This potential exaptation of a microphagous filter feeding strategy for fish foraging enables humpback whales to achieve 7× the energetic efficiency (per lunge) of krill foraging, allowing for flexible foraging strategies that may underlie their ecological success in fluctuating oceanic conditions.

The influence of tourism-based provisioning on fish behavior and benthic composition.

Distribution of non-natural food (provisioning) to attract fish, though popular in coral reef tourism, has often been discouraged due to its assumed adverse effects on fish health and behavior. However, the effects of provisioning on community structure, anti-predator, and foraging behavior of teleost fishes, as well as their potential to indirectly affect benthic organisms, are not yet clear. Here, we compared fish composition, wariness, foraging behavior of herbivorous fishes, and the benthic cover between provisioned and control sites. We found significant differences in fish abundance, species number, and composition at some locations, but not all. Although most provisioned herbivorous fish did not reduce their biting rates of benthic algae, provisioned sites still had higher coverage of green macroalgae. Our results dispute widely held presumptions on the effects of tourism-based provisioning on the ecology and behavior of teleost fishes, as well as the benthic cover. These findings suggest that while regulation of provisioning is necessary to manage and mitigate any deleterious outcomes, when moderated and monitored, it could still provide an educationally beneficial tool for coral reef ecotourism.

UV-light and dietary vitamin D and their effects on ionized calcium and 25-OH-D plasma concentrations in captive gentoo penguins (Pygoscelis papua).

In this study, the effect of ultraviolet (UV) light and dietary vitamin D on calcium metabolism in permanently indoor-housed gentoo penguins (Pygoscelis papua) was investigated. The study consisted of three periods, each completed with blood samples to analyse plasma concentrations of 25-OH-D, 1,25-(OH)2 -D, ionized (iCa) and total calcium (tCa). During the first study period (D), animals were housed under routine conditions without UV-light and fed a diet of different fish species, supplemented with 1,000 IU vitamin D per animal and day. The following study period (Baseline) of 28-day duration consisted of the same diet without any vitamin D supplementation and without UV-light. During the study period (UVB) artificial UV-light was added for 3 weeks. The vitamin D content of fish was measured by high-performance liquid chromatography. It varied between fish species and between facilities, ranging from no measurable content in capelin (Mallotus villosus) to 7,340 IU vitamin D/kg original matter (OM) in herring (Clupea spp). The average dietary vitamin D content was 311 IU/kg OM at facility 1 and 6,325 IU/kg OM at facility 2, resulting in a vitamin D intake per animal and day without supplementation of 130 IU (25.5 IU/kg body weight BW) and 2,454 IU (438.2 IU/kg BW) respectively. The supplementation of vitamin D elevated significantly the plasma concentrations of 25-OH-D by an intraindividual difference of 15 (range -2 to 59) nmol/L and tCa by 0.1 (0.0-0.3) mmol/L only at facility 2. The exposure to UV-light raised the blood concentrations of tCa at facility 2 by 0.15 (0.1-0.2) mmol/L, and of iCa and tCa for females at facility 1 by 0.23 (0.13-0.41) mmol/L and 1.8 (1.1-2.5) mmol/L respectively. No significant influence of the study periods (D) and (UVB) was found for the concentrations of 1,25-(OH)2 -D at both facilities.

Longitudinal variation in fish prey utilization, trophic guilds, and indicator species along a large subtropical river, China.

Due to the heterogeneous distribution of resources along large rivers, understanding prey utilization by basin-scale fish assemblages remains a challenge, and thus, recognizing regional fish trophic guilds and indicator species is important. We analyzed the stomach contents of 96 fish species along the subtropical East River in China and identified 8 prey items (29 subcategories). Site-specific differences in fish diet composition (DC) revealed longitudinal shifts in utilized prey taxa, from upstream lotic to downstream semi-lentic items, and these were characterized by a decrease in the proportions of epilithic diatoms and aquatic insect larvae (Ephemeroptera and Chironomidae) accompanied by an increase in bivalves (Corbicula and Limnoperna), shrimps and fishes, and organic sediments. The relative prey consumption weighted by fish abundance and biomass indicated that decreasing insect consumption and increasing detritus consumption were two fundamental vectors governing fish-centered feeding pathways. Seventeen prey-oriented fish guilds that were clustered based on DC matrix determined the spatial variation in the fish trophic structure. The cumulative presence of (a) upstream guilds reliant on insects and epiphytes, (b) midstream guilds reliant on hydrophytes, molluscs, and nekton, and (c) downstream guilds reliant on detritus, annelids, and plankton resulted in a longitudinal increase in guild richness, but this continuity was interrupted near the industrialized estuary. The most abundant 28 fish species across the guilds were selected as trophic indicator species; their spatial distribution significantly (p < 0.05) explained >80% of the environmental and prey variables identified. These species signified the availability of predator-prey links in distinct habitats and the key environmental factors supporting these links. With a high contribution (>51%) of exotic species, an increase in detritivores downstream distinguishes the subtropical East River from temperate rivers. Particularly, in the disturbed lower reaches, the dominance of detritivores prevailed over the predicted increase in other feeding groups (e.g., omnivores and carnivores).

The effects of fish feeding by visitors on reef fish in a Marine Protected Area open to tourism / O efeito da alimentação artificial em peixes recifais em uma Área Marinha Protegida com atividade turística

Abstract: Coral reef-based tourism has risen sharply across the globe, coupled with an increase in fish feeding by visitors. Studies indicate that fish feeding is one of the leading causes of changes in distribution patterns, abundance, the structure of marine fish communities, and fish behavior. The aim of this study was to determine the effect of human presence and fish feeding on the behavior of reef fish by conducting in situ experiments in tide pools in a Marine Protected Area located at the northern limit of the Abrolhos Bank in the South Atlantic Ocean. Eight feeding sessions were conducted and filmed, resulting in a total of 160 minutes of video footage. Each filming session recorded four different experimental conditions alternating between human presence, human absence, and fish feeding. Our findings suggest that fish feeding may cause changes in fish behavior, such as habituation to human presence, conditioning to fish feeding, increased aggressiveness, attacks on humans, and short-term changes in species distribution. The continuation of fish feeding over time can cause an increase in the size of the populations of species that consume food provided during feeding and consequently trigger changes in the structure of communities.

Resumo: O uso turístico de recifes de corais tem aumentado fortemente em todo o mundo, e com ele o fornecimento de alimento aos peixes por humanos. Porém, estudos indicam essa atividade como causa de distúrbios nos padrões de distribuição, abundância, estrutura da comunidade e comportamento de peixes marinhos. O objetivo deste estudo foi determinar o efeito da presença humana e da alimentação artificial no comportamento dos peixes recifais, através de experimentos in situ realizados em piscinas de maré de uma Área Marinha Protegida no limite Norte do Banco dos Abrolhos, Atlântico Sul. Para isso foram realizadas 8 sessões (160 min) de filmagem remota do experimento de alimentação artificial. Cada sessão de filmagem registrou quatro tratamentos, os quais alternavam momentos de presença e ausência humana, e de alimentação dos peixes.Os resultados encontrados indicam que a alimentação artificial tem provocado alterações comportamentais nos peixes como a habituação à presença humana, condicionamento à oferta de alimento, aumento da agressividade, ataques a humanos e alterações na distribuição das espécies em curto prazo. A permanência da atividade de alimentação artificial, ao longo do tempo, pode provocar o aumento das populações que consomem o alimento oferecido e consequentemente, desencadear alterações na estrutura da comunidade.

Is coexistence between non-native and native Erythrinidae species mediated by niche differentiation or environmental filtering? A case study in the upper Paraná River floodplain

The limiting similarity theory predicts that divergence in the functional traits of native and introduced species is an essential component in species establishment, as introduced species must occupy a niche that is unoccupied by resident species. On the other hand, the environmental filtering hypothesis predicts convergence between introduced and native species, as both possess traits that make them adapted to the local abiotic environment. Morphology, spatial co-occurrence, diet, feeding selectivity, and niche breadth and overlap of Erythrinidae were evaluated to detect possible mechanisms acting in the coexistence between non-native and native species. Native (Hoplias sp. B and Hoplias cf. malabaricus) and non-native (Hoplerythrinus unitaeniatus and Hoplias mbigua) species presented differences in morphological traits, spatial co-occurrence, diet, selectivity, and niche breadth and overlap. The mechanisms mediating species coexistence seem to vary according to species. The absence of spatial and feeding overlap suggests that non-native species H. unitaeniatus occupy a different niche than native species, supporting its successful establishment without eliminating the native species. However, low feeding overlap and similar morphologies between non-native and native species of Hoplias point to environmental filters; in this case, the non-native H. mbigua is able to establish due to similarities in functional traits.(AU)

Teorias sobre nicho ecológico afirmam que divergência em traços funcionais entre espécies nativas e introduzidas são essenciais ao estabelecimento da espécie introduzida, pois estas devem ocupar um nicho não utilizado pelas espécies residentes. Por outro lado, a teoria de filtros ambientais afirma a convergência entre espécies introduzidas e nativas, pois ambas possuem traços funcionais que fazem com que essas espécies estejam mais adaptadas as variáveis ambientais. Foram avaliadas a morfologia, ocorrência espacial, dieta, seletividade alimentar, sobreposição e largura de nicho em Erythrinidae para detectar possíveis mecanismos atuando na coexistência de espécies nativas e não nativas. Espécies nativas (Hoplias sp. B e Hoplias cf. malabaricus) e não nativas (Hoplerythrinus unitaeniatus e Hoplias mbigua) apresentaram diferenças em todos os atributos testados. Os mecanismos mediando a coexistência de espécies nativas e não nativas parecem variar de acordo com a espécie considerada. A ausência de sobreposição espacial e na dieta sugere que a espécie não nativa H. unitaeniatus ocupa um nicho distinto que as espécies nativas, favorecendo seu estabelecimento sem eliminar as espécies nativas, apontando para segregação de nicho. Por outro lado, morfologias similares, porém com diferentes dietas foram observadas para as espécies de Hoplias, sugerindo que as espécies coexistem devido à filtros ambientais, assim, neste caso, a espécie não nativa H. mbigua é capaz de se estabelecer no novo ambiente devido à similaridades em traços funcionais.(AU)

Dietary burden calculations relating to fish metabolism studies.

Fish farming is increasingly dependent on plant commodities as a source of feed leading to an increased risk for pesticide residues in aquaculture diets and consequently their transfer into aquaculture food products. The European pesticide regulation requires fish metabolism and fish feeding studies where residues in fish feed exceed 0.1 mg kg(-1) of the total diet (dry weight basis) to enable the setting of appropriate maximum residue levels in fish commodities. Fish dietary burden calculation is therefore an important prerequisite to decide on further experimental testing as part of the consumer risk assessment. In this review, the different aquaculture production systems are compared with regard to their specific feeding practices and the principles of dietary burden calculation are described.

Clear as mud: a meta-analysis on the effects of sedimentation on freshwater fish and the effectiveness of sediment-control measures.

Increase in fine sediments in freshwater resulting from anthropogenic development is a potential stressor for fish and thus may cause population declines. Though a large body of literature exists on the topic, there have been few attempts to synthesize this information in a quantitative manner. Through meta-analysis we investigated the effects of sediment in lotic environments on resident ichthyofauna using ecologically-relevant endpoints for tolerant (e.g., northern pike Esox lucius) and intolerant (e.g., brook trout Salvelinus fontinalis) species. Further, the efficiency of sediment-control devices was explored to inform mitigation measures. An increase in suspended and deposited sediments was demonstrated to have a negative effect on all parameters and tolerances tested (feeding behavior [feeding rate, reaction distance to food item]; spawning success [survival of fry to eyed stage, fry emergence]; species richness; P < 0.001) except fish abundance (P = 0.058). Heterogeneity between studies was a factor in all analyses. Although there were insufficient studies to conduct meta-analysis on sediment-control devices, weighted percent efficiency estimates revealed that properly installed sediment-control fences tended to have a higher percent efficiency (73-80%) than sediment traps and basins (40-52%). These results highlight the negative impact that increases in suspended and deposited sediments can have on resident fishes from the individual to the population, and the need for more transparent and thorough statistical reporting. The analysis also identifies a clear need for rigorous experimental studies contrasting different sediment-control devices and strategies given that little such work has been published. That alone is remarkable given that sediment-control devices are often a requirement of regulators for riparian development activities, yet the evidence to support the effectiveness of the primary mitigative strategies is weak.

Sex-specific distribution and diet of Platichthys flesus at the end of spawning in the northern Baltic Sea.

This study examined the relationship of seascape structure, prey availability and sex on the post-spawning distribution and diet of European flounder Platichthys flesus in the northern Baltic Sea. The objectives were to determine whether: (1) wave exposure and substratum affect abundance and distribution of P. flesus, (2) diet reflects the benthic prey composition and (3) sex affects the distribution or diet of P. flesus. The results showed that P. flesus was evenly spread in the archipelago with no correlation to wave exposure. The distribution was, however, sex specific; reproductive males dominated the exposed zone and mainly post-reproductive females dominated the intermediate and sheltered zones. Platichthys flesus fed mainly on two bivalve prey species: blue mussels Mytilus edulis and Baltic tellins Macoma balthica. Hard substratum invertebrates dominated the diet in all habitats and apart from some typical soft substratum species, there was no clear link between fish feeding and the dominance structure of benthic prey. Diet was further sex specific, with females showing a broader range of diet than males. Results suggest that P. flesus is a specialist molluscivore found commonly and equally in soft- and hard-substratum habitats throughout the archipelago area. Previous studies on P. flesus in the Baltic Sea have yielded inconsistent results regarding diet and it has commonly been believed that the distribution of Baltic Sea P. flesus is linked to sand and soft substrata. The present findings emphasize the importance of including the entire range of habitats when diet and regional species distributions are assessed.

Trophic ecology of Saccodon dariensis (Pisces: Parodontidae) in Guatapé River tributaries, Magdalena River Basin, Colombia / Ecología trófica de Saccodon dariensis (Pisces: Parodontidae) en afluentes del río Guatapé, Cuenca río Magdalena, Colombia

Objective. To study the trophic ecology of Saccodon dariensis in the Peñoles and El Cardal streams, Guatape River mid-basin, Magdalena River Basin, Colombia. Materials and methods. To compare differences in size between individuals from the two streams in terms of hydrologic periods, oral polymorphisms or sexes, an analysis of variance was conducted (ANOVA). Volume percentages, frequency of occurrence and the food importance index (FII) were determined; a principal component analysis (PCA) and an ANOVA was carried out to determine the diet differences between streams, climatic periods, oral polymorphism, sexes and developmental states, as well as a Mann-Whitney pairwise comparison test for each food category. Results. A significant difference was found in size between individuals of the two streams with different oral polymorphism. Algae are the most important food item (FII: 91.9%), followed by Trichoptera and insect remains (FII: 4.3%), and vegetal material (FII: 1.8%). The PCA did not indicate significant differences in diet between streams, climatic periods, oral polymorphisms, sexes or developmental states, but the ANOVA and Mann-Whitney pairwise comparison test indicated differences in oral morphotype, where individuals with a straight mouth consumed more vegetal material. We also observed different proportions in consumption of different algae genera, and increased consumption of insects in ontogeny, this being higher in individuals with a straight mouth. Conclusions. The species is algaevorous. The oral morphotypes of S. dariensis may be related to a trophic polymorphism that confers different trophic habits and differential access to the items that constitute their diet.

Objetivo. Estudiar la ecología trófica de Saccodon dariensis en las quebradas Peñoles y El Cardal, parte media del río Guatape, cuenca del rio Magdalena, Colombia. Materiales y métodos. Para contrastar diferencias entre individuos de las dos quebradas en cuanto a períodos hidrológicos, polimorfismos bucales y sexos se realizó un análisis de varianza (ANOVA). Se determinó los porcentajes de volumen, frecuencia de ocurrencia e índice de importancia alimentaria (IIA); se realizó un análisis de componentes principales (ACP) y un ANOVA para determinar diferencias de dieta entre quebradas, períodos climáticos, polimorfismos bucales, sexos, estados de desarrollo, y una prueba de comparación por pares de Mann-Whitney para cada categoría de alimento. Resultados. Se encontró diferencia significativa en la talla entre individuos de las dos quebradas con diferente morfotipo bucal. Las algas es el ítem de alimento más importante (IIA: 91.9%), seguido por Trichoptera y restos de insectos con (IIA: 4.3%) y material vegetal (IIA: 1.8%). El ACP no indicó diferencias en la alimentación entre quebradas, períodos climáticos, polimorfismo bucal, sexos o estados de desarrollo, pero la ANOVA y la prueba de Mann-Whitney indicaron diferencias por morfotipo bucal, donde individuos de boca recta consumen más material vegetal. Se observó en proporciones diferentes el consumo de diferentes géneros de algas, y aumento de consumo de insectos en ontogenia, siendo más alto para individuos de boca recta. Conclusiones. La especie es alguivora. Los morfotipos bucales en S. dariensis pueden estar relacionados con un polimorfismo trófico que le confiere diferentes hábitos tróficos y acceso diferencial a los ítems que constituyen su dieta.

EVALUACIÓN DE UN SISTEMA DE ALIMENTACIÓN ORGÁNICO SOBRE EL DESEMPEÑO PRODUCTIVO DE LA TILAPIA NILÓTICA (Oreochromis niloticus) CULTIVADA EN ESTANQUES DE TIERRA / EVALUATION OF AN ORGANIC FEEDING SYSTEM ON THE PRODUCTIVE PERFORMANCE OF NILE TILAPIA (Oreochromis niloticus) IN EARTHEN PONDS

Se evaluó el efecto de un sistema de alimentación integrado por dietas formuladas con recursos alternativos orgánicos y diferentes niveles de fertilización orgánica sobre parámetros zootécnicos en peces de consumo cultivados en estanques de tierra. Se utilizaron 1.324 juveniles de Tilapia nilótica (Oreochromis niloticus) cuyo peso inicial promedio fue de 161,9 ± 7,0 g, solo machos sexados manualmente, sin reversión hormonal. Se empleó un diseño completamente al azar con tres tratamientos y tres repeticiones, distribuidos en 9 estanques de tierra (200 m² cada uno), cultivados bajo las normas de Naturland (2007, 2008, 2011) para la acuicultura orgánica. Durante 180 días se suministraron dietas (levante: 27% PB y 4.120 cal/g EB; finalización: 21% PB y 4.200 cal/g EB) formuladas con recursos provenientes de producción agrícola orgánica certificada. Se implementaron tres variables: un control sin fertilizante y dos diferentes niveles de fertilización con gallinaza orgánica (T1: Abonamiento intensivo con 5 g/m²/día; T2: Abonamiento periódico con 14 g/m²/semana y T3: Sin abonamiento). Se evaluó el efecto de los tratamientos sobre parámetros productivos: ganancia diaria de peso, conversión alimenticia aparente, tasa de crecimiento específico, rendimiento en filete, índices viscerosomático, hepatosomático y de grasa visceral, relación de eficiencia proteica, valor productivo de proteína y eficiencia de retención de energía. No se encontraron diferencias significativas en las variables evaluadas (p>0.05). Los resultados indican la posibilidad de implementar un sistema de alimentación orgánico como alternativa productiva que logra parámetros productivos que se aproximan a lo reportado para explotaciones convencionales de tilapia y con el potencial de posicionar un producto final en eco-mercados diferenciales siendo sustentable en su obtención.

It was evaluated the effect of a feeding system that included formulated diets with organic alternative resources and different levels of organic fertilization on animal production evaluation parameters in fish farmed in earthen ponds. 1,324 juvenile Nile tilapia (Oreochromis niloticus) with initial weight of 161.9 ± 7.0 g, male manually sexed without hormonal reversal were used. It was used a completely randomized design with three treatments and three replicates, randomly distributed in 9 earthen ponds of 200 m² each. The husbandry management was under the Naturland standards for organic aquaculture. During 180 days fish were fed diets (growth: 27% CP and 4,120 cal/g GE; finish: 21% CP and 4,200 cal/g GE) formulated using resources from certified organic agricultural production. Were handled without fertilizer control and two different levels of organic chicken manure fertilization (T1: intensive fertilization with 5g/m²/day; T2: periodically fertilization with 14g/m²/week and T3: no fertilization). The effect of treatments was evaluated on: daily weight gain, apparent feed conversion, specific growth rate, fillet yield, viscerosomatic, hepatosomatic and visceral fat index, protein efficiency ratio, protein production value and energy retention efficiency. There were not significant differences in the variables evaluated (p<0,05). Results obtained suggest that it is possible to implement an organic feeding system to be a productive alternative that able to maintain production parameters approximate to that reported to conventional production, with potential to position the final product markets to be sustainable differential extraction.