Trophic morphoecology in the genus barbus (pisces, cyprinidae)

In this paper the morphological features and feeding habits of three coexisting Barbus species in the Tajo basin (Spain) were studied. Fifteen biometric measurements of each specimen were taken, then eleven morphological variables were calculated, and at the same time, the gastnc contents of each individual were analyzed. The results showed and important relationship of barbillon length, body form, branchial filter and buccal apparatus to size, distribution and food items. The exploitation of available resources in the reservoirs is discussed in the light of the discriminant body differences of the specie

The Iberian ichthyofauna : ecological contributions

The actual Iberian ichthyofauna is the result of the functioning of the aquatic systems and the human activities. For 27 years the Fish Ecology Research Group of Seville University has worked on understanding the complex relationships established around fish in different water systems and from differents approach scales (life strategies, population dynamics, structure and diversity of the communities, energy, etc.). The work carried out through those years has yielded a huge increase in the knowledge of our continental ichthyofauna. Now we are getting closer to understanding the Iberian epicontinental ecosystems and the ecology role of their fish, a basic need for management and conservation purposes.La actual ictiofauna ibérica es el resultado tanto del funcionamiento de los ecosistemas acuáticos como de las actividades humanas. Durante 27 años, el Grupo de Investigación de Ecología de Peces de la Universidad de Sevilla ha trabajado en la comprensión de las complejas relaciones que giran en torno a la ecología de los peces de nuestros diferentes ecosistemas epicontinentales, abordándolos desde distintas aproximaciones (estrategias de vida, dinámica de sus poblaciones, estructura y diversidad de sus comunidades, energéticas, etc). Los estudios llevados a cabo a lo largo de estos años han contribuido a incrementar el conocimiento de los ecosistemas acuáticos epicontinentales de la Península Ibérica y el papel ecológico de sus peces, conocimientos ambos básicos para el manejo y la conservación de los mismos

Trophic habits of the fish assemblage in an artificial freshwater ecosystem: the Joaquín Costa reservoir, Spain

The Joaquín Costa reservoir contains a mixed fish assemblage of native and exotic species. Feeding habits and feeding relationships of species in the fish assemblage were analysed over a one year cycle. Differences in diet composition were found both between species and within species among seasons. Food overlap and trophic similarity among species also showed seasonal variations. Cluster analysis differentiated four groups of predominant diet: (1) macroinvertebrates (trout and largemouth bass), (2) detritus (nase), (3) cladoceran crustaceans and (4) an omnivorous feeding regime, with large seasonal variations in food habits. Food of fish species included in groups 3 and 4 (roach, white bream, barbel, common and mirror carp) varied seasonally. Using graphical models of feeding strategies, similarity indexes, cluster and multivariate analyses based on the relative importance of food categories in the diet of the species, we illustrate that the fish assemblage showed food resource partitioning according to food habits and foraging habitats within the reservoir

Feeding ecology of the Ruivaco Achondrostoma oligolepis, a Portuguese endemic cyprinid fish

This study assessed the feeding ecology of the ruivaco Achondrostoma oligolepis, a Portuguese endemic resident cyprinid fish whose dietary habits are virtually unknown. Samples were taken seasonally in three medium-sized rivers representing a gradient of temporality. The stomach contents of 97 individuals (42-126 mm total length, TL) were analysed. Although there was no significant overall variation in diet composition between rivers, differences were found among seasons. A broad range of food categories was identified, although a smaller subset of primarily detritus (77.6 %) and plant material (18.4 %) constituted the base diet. Of the animal prey, Coleoptera and Diptera were the most prevalent, occurring in 13.2 % and 9.8 % of the fish, respectively, and were consumed mainly in the spring. Based on the observed diet composition and feeding strategy, the ruivaco could be considered a generalist, foraging on the most abundant and available preyEste estudio evaluó la ecología alimentaria del ruivaco (Achondrostoma oligolepis), un ciprínido endémico de Portugal cuyos hábitos alimenticios son prácticamente desconocidos. Las muestras fueron recogidas estacionalmente, en tres ríos medianos representando un gradiente de temporalidad. Los contenidos estomacales de 97 individuos (42-126 mm de longitud total, LT) fueron analizados. Aunque en general no hubo variación significativa en la composición de la dieta entre ríos, sí se encontraron diferencias entre las estaciones. Se identificó una amplia gama de categorías de alimentos, aunque un subconjunto más pequeño conformó la base de la dieta, encontrándose principalmente dominada por detritus (77.6 %) y material vegetal (18.4 %). Los coleópteros y dípteros fueron los grupos más frecuentes entre las presas animales, siendo encontrados en el 13.2 % y el 9.8 % de los peces respectivamente, y consumidos principalmente en primavera. Con base en la composición de la dieta y en la representación de la estrategia trófica, el ruivaco puede ser considerado como generalista, alimentándose de las presas más abundantes y disponible

Hydroacoustics for density and biomass estimations in aquaculture ponds

The use of hydroacoustics is currently being studied and developed as a promising non-intrusive methodology to monitor and manage fish stocks in aquaculture farms. The main objective of this study was to develop an acoustic method for the estimation of fish density and biomass in inland aquaculture farms and test the accuracy and precision of the estimates with real data provided by the company. The study was conducted in sea bass (Dicentrarchus labrax) production ponds located in Seville (Southern Spain). A Simrad EK60 echosounder with two split-beam circular transducers operating simultaneously at 200 kHz was used for hydroacoustic surveys. Two different hydroacoustic designs were considered: central trajectories and zigzag trajectories. The accuracy and precision of the estimates were examined in order to select the best sampling design. Due to a non-homogeneous fish distribution in the pond caused by the avoidance behaviour, as a response to the sampling disturbance presented by fish, acoustic density and biomass were corrected by applying sampling theory according to the probability of fish detection. When density and biomass were corrected, the estimates became highly accurate and precise with respect to real data, which confirms that the proposed method is adequate. Similarly, acoustic estimates of fish weight were highly in agreement with real data, due to the use of specific equations developed “in situ” for the study. Although no significant differences were recorded in the density and biomass estimates with regard to the trajectory used (central vs. zigzag), it was observed that the most accurate agreement and precision were always obtained in central trajectories. Therefore, central design is proposed as the most appropriate design for hydroacoustic measurements in inland ponds. The results obtained in this study provide estimates of density and biomass that accurately match the real data, supporting the use of hydroacoustics as a potentially valid tool to manage inland aquaculture farms

Testing of new sampling methods and estimation of size structure of sea bass (Dicentrarchus labrax) in aquaculture farms using horizontal hydroacoustics

In aquaculture, monitoring fish size and density is fundamental to improve management and profitability of fish farms. The aim of this study is to test whether horizontally aimed 200-kHz transducers are adequate to obtain fish size structure in open-sea cages in order to apply horizontal hydroacoustics as a non-intrusive and innovative technique in sea bass (Dicentrarchus labrax) farming. Several sampling strategies have been tested by placing the transducer in two different positions: outside the cage and inside the cage. In addition, two sampling approaches have been implemented: placing the transducer at a fixed position or moving it vertically. The results show that horizontal hydroacoustics is a useful technique for monitoring size distribution of sea bass in farming cages. The most adequate sampling method consists of using a vertically moving transducer positioned outside the cage, since it exhibits the narrowest size distributions with the lowest variance estimates, which matches the data provided by fish farmers

Life strategies in fish species inhabiting fluctuating streams in South Spain: a holistic conception

Nuestro trabajo revisa los resultados obtenidos desde 1987 a 1992 sobre la ¡ctiofauna del río Guadalete (SW España), donde se relacionan las características particulares de los estilos de vida que presentan las especies de peces con los factores ambientales (características físico-químicas del medio y la disponibilidad de alimento). El Guadalete se caracteriza por ser un río de régimen mediterráneo y su ictiofauna está compuesta solamente por tres especies de ciprínidos: Barbiis sclateri (76%), Chondrostoma polylepis willkommi (17%) y Leiiciscus pyrenaicus (7%). Las tres especies presentan la misma estrategia de vida caracterizada por: esperanza de vida corta, tasa de crecimiento elevada, temprana edad de maduración sexual, pequeña longitud en la maduración y primera puesta, alta inversión reproductora, elevada fecundidad y hábitos alimentarios generalistas. A pesar de presentar la misma estrategia, se detectan diferencias entre ellas debido a que desarrollan tácticas diferentes.The paper reviews the relationships between the life-history strategies and habitat characteristics (physic-chemical variables of the environment and resource availability) of three cyprinid species inhabiting a fluctuating stream (Guadalete, Southern Spain) since 1987 to 1992. The Guadalete River has a Mediterranean régimen and a fish assemblage composed exclusively by Barbus sclateri (76%), Chondrostoma polylepis willkommi (17%) and Leuciscus pyrenaicus (7%). The life strategy of these three fish species is characterised by: short life span, high growth rate, early age at maturity, small length at maturity and first breeding, high reproductive investment, high fecundity and generalist feeding habits. Nevertheless, in spite of showing the same strategy, differences have been detected among them due to having developed different tactics.Comisión Interministerial de Ciencia y Tecnología de España (CICYT) NAT89-109

Biomass and abundance biases in European standard gillnet sampling

The European Standard EN 14757 recommends gillnet mesh sizes that range from 5 to 55mm (knot-to-knot) for the standard monitoring of fish assemblages and suggests adding gillnets with larger mesh sizes if necessary. Our research showed that the recommended range of mesh sizes did not provide a representative picture of fish sizes for larger species that commonly occur in continental Europe.We developed a novel, large mesh gillnet which consists of mesh sizes 70, 90, 110 and 135mm (knot to knot, 10m panels) and assessed its added value for monitoring purposes. From selectivity curves obtained by sampling with single mesh size gillnets (11 mesh sizes 6 – 55mm) and large mesh gillnets, we identified the threshold length of bream (Abramis brama) above which this widespread large species was underestimated by European standard gillnet catches. We tested the European Standard gillnet by comparing its size composition with that obtained during concurrent pelagic trawling and purse seining in a cyprinid-dominated reservoir and found that the European Standard underestimated fish larger than 292mm by 26 times. The inclusion of large mesh gillnets in the sampling design removed this underestimation. We analysed the length-age relationship of bream in the Římov Reservoir, and concluded that catches of bream larger than 292mm and older than five years were seriously underrepresented in European Standard gillnet catches. The Římov Reservoir is a typical cyprinid-dominated water body where the biomass of bream > 292mm formed 70% of the pelagic trawl and purse seine catch. The species-specific relationships between the large mesh gillnet catch and European Standard catch suggested that the presence of carp (Cyprinus carpio), European catfish (Silurus glanis), tench (Tinca tinca) or bream warrants the use of both gillnet types.We suggest extending the gillnet series in the European Standard to avoid misinterpretation of fish community biomass estimate