Abstract
Examination of brown trout seasonal diet variation and investigation of terrestrial prey importance in a food-rich stream using four indices of prey importance (number and weight abundance, frequency of occurrence, index of relative importance) revealed that aquatic prey constituted the major part of the diet (>90%) throughout the examined period. Despite Gammaridae being the most abundant in the environment, other less abundant organisms appeared to be important prey, including terrestrial organisms, with maximum consumption in September. The electivity index showed a positive selection of rare prey types; Tokeshi’s model revealed a specialist strategy for most of the population, except for those of 1+ age, who were inclining to generalist strategy. Diet diversity increased throughout April to October, and ages 1+ and 2+ exhibited a more diverse diet than older ages. Diet overlap between age classes was considerable, with less overlap observed in the later season. This pattern of differentiation in the diet of brown trout age classes and their feeding plasticity over seasonal scales, as observed in this food-rich stream, provides a starting point for further examination of this topic in streams with similar or different food richness and availability.
Highlights
The socioeconomic importance of brown trout (Salmo trutta L., 1758) as an attractive fish species in recreational fishing puts this species in the spotlight of numerous ecological studies [1,2,3,4,5,6,7,8,9,10,11]
The condition factor was lowest for age class 0+ and highest for the oldest classes (Table 1)
This study provides insight into the complex brown trout feeding habits during one season at a locality that can be considered an example of a food-rich limestone stream
Summary
The socioeconomic importance of brown trout (Salmo trutta L., 1758) as an attractive fish species in recreational fishing puts this species in the spotlight of numerous ecological studies [1,2,3,4,5,6,7,8,9,10,11]. Aside from a few basic requirements it shares with other salmonids, brown trout has a worldwide distribution and can live in habitats that may differ significantly, making each local study a valuable contribution to knowledge about the feeding patterns and ecological plasticity of this species. Life in a stream or a small river is challenging, with the fish foraging while constantly struggling with water flow and the fluctuating quantity and quality of available food. For these reasons, stream-dwelling brown trout has slower growth rates [14] in comparison with migratory, sea, or lake trout, which inhabit the more resilient ecosystems of oceans and lakes. Brown trout mainly feed on small benthic invertebrates
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