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

Abstract

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 and Food Selection of Endemic <I>Squalius Carolitertii</I> (Actinopterygii: Cypriniformes: Cyprinidae) in River Tormes, Central Spain, in Summer

“…This study shows that the size-frequency distribution of gastrointestinal tracts was not identical to that in the benthos and drift samples. This supports the findings of Sánchez-Hernández et al (2011a) who found that the size-frequency distribution of potential prey items in the benthos was different to that of prey in the stomachs of brown trout. Our findings are in concordance with the observations of brown trout by Rincón and Lobón-Cerviá (1999), and prey-size selection is probably dependent of the characteristics of the size-frequency distribution of the available prey.…”

“…Moreover, the preference for Baetis spp. found in this study could also be related to site-specific prey accessibility as demonstrated by other researchers (Oscoz et al 2006, Johnson et al 2007, Leunda et al 2008, Sánchez-Hernández et al 2011a.…”

“…On the other hand, according to several authors prey size and other factors related to fish size including, for example, handling ability of fishes are important variables that determine food selection (Cunha and Planas 1999, de Crespin de Billy et al 2002, Sánchez-Hernández et al 2011a). This study shows that the size-frequency distribution of gastrointestinal tracts was not identical to that in the benthos and drift samples.…”

“…A better knowledge of the feeding habits of S. carolitertii would provide important information to help understand the trophic requirements of this fish. Several researchers have demonstrated that studies based on food selection provide insight into factors involved in prey choice in freshwater fish species (Rincón and Lobón-Cervía 1999, Johnson et al 2007, Sánchez-Hernández et al 2011a. Hence, the goal of this research was to study the ontogenetic dietary shifts and food selection of S. carolitertii in an Iberian river during summer, contributing to the knowledge of the feeding behaviour of this fish species.…”

Age-related differences in prey-handling efficiency and feeding habitat utilization of Squalius carolitertii (Cyprinidae) according to prey trait analysis

“…In addition, fishes can acquire foraging information from conspecifics (Reader et al 2003 and references therein), and as the predator acquires experience, the development of a search image can improve the ability to detect food, helping to account for the greater foraging efficiency observed in adults (Ware 1971;Morrison et al 1978). Handling ability of fishes is an important variable that may determine food selection (Cunha & Planas 1999;de Crespin de Billy & Usseglio-Polatera 2002;Sánchez-Hernández et al 2011a). In this sense, Oscoz et al (2006) stated that prey-handling costs in Cyprinidae species could be responsible for the observed inter-and intra-specific (size-related) changes in diet preferences.…”