Rufino Vieira-Lanero

Feeding habits of four sympatric fish species in the Iberian Peninsula: keys to understanding coexistence using prey traits

Trophic interactions are important factors structuring animal communities. We assessed the trophic relations of four fish species that live in sympatry in the River Ladra (NW Spain), and cluster analysis differentiated two feeding strategies: (1) species with omnivorous feeding habits, feeding mainly on detritus and plant material but with aquatic macroinvertebrates as an important complement (Achondrostoma arcasii and Pseudochondrostoma duriense) and (2) species feeding mainly (Salmo trutta) or exclusively (Gasterosteus gymnurus) on aquatic macroinvertebrates. Concerning ingested macroinvertebrates, the trophic overlap was quantified using Schoener’s index and the results obtained revealed a high diet overlap among the species (from 81.3 up to 99.2%). In order to get a deeper insight into mechanisms of fish species coexistence, we used ten biological and ecological traits of macroinvertebrate prey to discriminate feeding preferences. As a result, despite the high similarity among the diets, our analyses suggest that differences in diel activity patterns and drift behaviour of preys, as well as differences in the prey size, are important adaptive features that may reduce the inter-specific competition in the fish community and permit the partitioning of food that allows coexistence.

Downstream migration and hematophagous feeding of newly metamorphosed sea lampreys (Petromyzon marinus Linnaeus, 1758)

The metamorphosis of sea lamprey (Petromyzon marinus Linnaeus, 1758) allows young postmetamorphic individuals to migrate to the sea and start the hematophagous feeding. However, the information about this phase is very limited, especially for European populations. Herein, we provide for the first time a comprehensive study on the phenology of downstream migration, the timing and location of first feeding and the prey species in the River Ulla and its estuary (NW Spain). Results show that downstream migration occurs between October and May with a peak in March. At least for a part of the postmetamorphic lampreys this migration stops for several months when they reach the estuary, where lampreys find shelter and abundant food, before moving to coastal waters. Hematophagous feeding in the estuary allows postmetamorphics to increase their total length and weight exponentially. Our results also suggest that part of the postmetamorphics (10–30%) start the hematophagous feeding in the river, with a special affinity for anadromous species, probably because of their larger size.

First feeding diet of young brown trout fry in a temperate area: disentangling constraints and food selection

Diet composition of newly emerged brown trout fry in natural areas remains poorly known, and foraging abilities at this early stage, although presumably reduced, are still under discussion. We have studied gut content composition of brown trout fry in a temperate area (Galicia, NW Spain) and compared it to the benthic macroinvertebrate community. Small prey such as chironomid larvae and baetid nymphs were the most important food items for newborns, some of them still presenting yolk remnants. However, the positive selection observed for Polycentropodidae and Simuliidae and the rejection of Elmidae and Leuctricidae suggest that other factors apart from size, such as locomotor abilities of fish or accessibility and antipredator behaviour of prey play an important role in feeding behaviour. Additionally, analysis of diet changes on the studied fry suggests a dramatic shift in niche breadth at the moment of complete yolk absorption, which might be related to the improvement of swimming and handling ability of fry for capturing and ingesting prey. The presence of aerial imagoes only in the stomachs of fry with no yolk provides further support to this hypothesis. Planning of restoration works on spawning grounds should then allow enough time for complete recolonization by benthic macroinvertebrates, including first instars, as searching for food in newborns is limited to the nest area due to mobility constraints.

Ontogenetic Dietary Shifts in a Predatory Freshwater Fish Species: The Brown Trout as an Example of a Dynamic Fish Species

The brown trout (Salmo trutta) is a species of Eurasian origin, but at has become naturalized in many other parts of the world. It has an outstanding socio-economic importance, both in commercial and sport fisheries, and it is frequently used as tourist attraction [1,2]. The case of brown trout is a clear example of a ‘dynamic’ fish species, as its diet and feeding behaviour can vary greatly among individuals, age classes, seasons and rivers. The composition of brown trout diet is strongly influenced by environmental and biotic factors. For example, water temperature plays an important role, as it influences food intake and the activity of fishes [3], but also the emergence and activity of aquatic insects or other potential prey items. Also water flow rate can be extremely important for drifting feeders such as brown trout, as they regulate food availability. The are many abiotic factors that influence feeding behaviour, but in general, biotic factors such as the locomotor ability of fishes, accessibility, abundance and antipredator behaviour of prey are thought to be the most important factors in the determination of the diet and feeding strategies in fishes. Usually not all the available prey is consumed by the predator, a feature that allows biologists to distinguish between trophic base and trophic niche (Figure 1). The trophic base consists of all potential prey items that the brown trout is able to consume and it is determined by the feeding habits of the fish, the size of the mouth and the anatomical characteristics of its digestive tract. However, the trophic niche is the variety of organisms that are really consumed by the predator, which depends on different factors that play an important role when choosing criteria prey items as, for example, prey abundance, including site-specific

Prey trait analysis shows differences in summer feeding habitat use between wild YOY Atlantic salmon and brown trout

Abstract We evaluated the vertical use of the water column for feeding by young of the year (YOY) of brown trout (Salmo trutta) and Atlantic salmon (S. salar) in a natural river during the summer. Prey trait analysis and diet composition demonstrated that brown trout showed a higher ability to feed on prey in the surface of the water column than Atlantic salmon. Hence, the differences in the ability to feed at different depths of the water column (surface vs. bottom) are important adaptive features that may reduce interspecific competition between the two sympatric fish species. Finally, results derived from the prey trait analysis provide useful information on resource partitioning between sympatric salmonid species.

Organic pollution induces domestication-like characteristics in feral populations of brown trout (Salmo trutta)

Sewage pollutants may impair growth or survival of the freshwater biota, though animals might benefit from the extra food availability as production increases. We examined biochemical (muscle glycogen), morphological (condition factor and hepatosomatic index), and diet biomarkers in brown trout for evaluating the effects of chronic exposure to organic pollution. Trout were collected at three locations: ST1 downstream of a trout farm, ST2 affected by the effluents of a wastewater treatment plant and ST3, the reference site. Individuals at polluted sites showed high hepatosomatic index, although no differences were found between ST2 and ST3 for the condition factor. A significant reduction was detected in the levels of muscle glycogen of individuals captured at polluted sites. Moreover, trout diet in these rivers was dominated quantitatively by Chironomidae and Simuliidae, in contrast with the diverse diet of individuals at ST3. Remarkably, individuals at polluted sites showed high stomach fullness and energy gut values, which might be considered as a case of hyperphagia. Our findings suggest that food surplus in organic enriched sites, in the form of high densities of macroinvertebrates, provide an environment similar to that of domesticated animals, where individuals might adopt less energetically costly behavioural strategies to ingest more food.

The larva of Drusus bolivari (McLachlan, 1880) (Trichoptera: Limnephilidae: Drusinae)

The hitherto unknown fifth instar larva of Drusus bolivari (McLachlan, 1880) is described for the first time and compared with other known similar Iberian species. The most important features are illustrated, and some zoogeographical and ecological notes are included. The thick pronotal ridge of D. bolivari is the main character to clearly distinguish this larva from those of the remaining known Iberian species of this genus. The most similar larva is that of Anomalopterygella chauviniana (Stein, 1874), but a deep dorsomedian gap occurs in the pronotal ridge of D. bolivari that is absent in that of A. chauviniana.

The larva and female of Rhyacophila fonticola Giudicelli & Dakki, 1984 (Trichoptera: Rhyacophilidae), an interesting Betic–Rifean endemic species

The female and last instar larva of the hitherto unknown Betic–Rifean species Rhyacophila fonticola Giudicelli & Dakki, 1984 are described and figured for the first time. Some notes on male variability and ecological preferences of this species are also included. The female is clearly different from that of the remainder species of the vulgaris group in the valvar structure of segment VIII. The larva belongs to the “Pararhyacophila group”, but an unusual character makes this species unique within this group: there are two gill tufts on each side of the first abdominal segment. This character makes the larva of R. fonticola clearly different from the remaining known Iberian species.

Densities and biomass of larval sea lamprey populations (Petromyzon marinus Linnaeus, 1758) in north-western Spain and data comparisons with other European regions

Although the sea lamprey, Petromyzon marinus Linnaeus, 1758, is a threatened species in Europe, available data on the condition and dynamics of its populations are very limited. Thus, electrofishing surveys were conducted annually between 2007 and 2011, so as to study the status and trends of larval populations of P. marinus in north-western Spain. In addition, data from other European regions were compiled. The density and biomass (mean±standard error) of ammocoetes in selected areas of larval habitat in north-western Spain were 11.0±1.44 individuals m–2 and 15.1±2.64g m–2, and showed signs of a population increase during the study period. However, conservation status of P. marinus was not considered favourable because of several factors, such as the widespread presence of obstacles (restriction of migration and habitat availability), along with some cases of organic pollution. Results and available data suggest that the largest populations of P. marinus as well as the main fisheries are located throughout the south-western areas of Europe (north-central Portugal, north–north-west of Spain and west–south-west of France). Signs of population increases were also registered in other European regions; however, more data are needed to confirm whether this trend has any relevance to a possible overall recovery.

The Immature Stages of Ptilocolepus extensus McLachlan, 1884 (Trichoptera: Hydroptilidae: Ptilocolepinae) with Notes on Biology

The last instar larva and the pupa of Ptilocolepus extensus McLachlan, 1884, an endemic of the Iberian Peninsula, are described for the first time. The final instar larva of Pt. extensus bears close resemblance to those of Ptilocolepus granulatus (Pictet, 1834), but the abdomen has a well-developed dorsal sclerotized plate on segment VIII; this is a morphological feature which has not been observed in any other Ptilocolepinae. Final instar larvae make dorsoventrally flattened, elongate-oval cases of leaf pieces from several moss and liverwort species; such cases are characteristic of the Ptilocolepinae. Some additional data on biology and geographical distribution are given.