Abstract
1. Stream dwelling fishes acquire most of their dietary energy by
consumption of aquatic and terrestrial macroinvertebrates. These prey
subsidies supply similar amounts of energy and macronutrients, but the
fact that terrestrial macroinvertebrates have lower contents of omega-3
long-chain polyunsaturated fatty acids (n-3 LC-PUFA), such as
eicosapentaenoic acid (EPA), than aquatic macroinvertebrates is largely
neglected.
2. EPA is a precursor for synthesis of docosahexaenoic acid (DHA), which
is an important structural lipid representing about a third of all fatty
acids in the brain of stream dwelling fishes. Laboratory studies have
shown a positive impact of DHA on brain development and cognition in
fishes. However, little is known how diet quality influences the DHA
content of brain tissues and its effect on fish brain development in the
wild.
3. Here we use previously demonstrated shift towards higher reliance on
n-3 LC-PUFA poor terrestrial prey of native brown trout Salmo
trutta living in sympatry with an invasive brook trout Salvelinus
fontinalis to explored how dietary deprivation of n-3 LC-PUFA affects
biochemical composition of tissues and brain volume and morphology of
wild fish.
4. We found that higher reliance on terrestrial prey of sympatric brown
trout resulted in lower EPA content in muscle tissues. The DHA content
in muscles did not differ between allopatric and sympatric brown trout,
but it decreased in sympatric brown trout with increasing reliance on
terrestrial prey. The brain volume, but not brain morphology, was
positively related to content of DHA in muscle tissues in sympatric and
allopatric brown trout.
5. Our study demonstrates that reliance on subsidies from terrestrial
food-web can have significant impact on brain development of wild
fishes. We showed effects of reduced dietary intake of n-3 LC-PUFA
induced by co-existence with an invasive species; however, other
anthropogenic factors such as climate change can further reduce the
availability of dietary n-3 LC-PUFA for stream dwelling fishes and other
consumers. This emphasises the need for further research on how dietary
availability of n-3 LC-PUFA in prey affects behaviour and physiology of
animals in the wild.