Abstract
Stable isotope analysis of commercially and ecologically important fish can improve understanding of life-history and trophic ecology. However, accurate interpretation of stable isotope values requires knowledge of tissue-specific isotopic turnover that will help to describe differences in the isotopic composition of tissues and diet. We performed a diet-switch experiment using captive-reared parasite-free Eurasian perch (Perca fluviatilis) and wild caught specimens of the same species, infected with the pike tapeworm Triaenophorus nodulosus living in host liver tissue. We hypothesize that metabolic processes related to infection status play a major role in isotopic turnover and examined the influence of parasite infection on isotopic turn-over rate of carbon (δ13C), nitrogen (δ15N) and sulphur (δ34S) in liver, blood and muscle. The δ15N and δ13C turnovers were fastest in liver tissues, followed by blood and muscle. In infected fish, liver and blood δ15N and δ13C turnover rates were similar. However, in infected fish, liver and blood δ13C turnover was faster than that of δ15N. Moreover, in infected subjects, liver δ15N and δ13C turnover rates were three to five times faster than in livers of uninfected subjects (isotopic half-life of ca.3-4 days compared to 16 and 10 days, respectively). Blood δ34S turnover rate were about twice faster in non-infected individuals implying that parasite infection could retard the turnover rate of δ34S and sulphur containing amino acids. Slower turnover rate of essential amino acid could probably decrease individual immune function. These indicate potential hidden costs of chronic and persistent infections that may have accumulated adverse effects and might eventually impair life-history fitness. For the first time, we were able to shift the isotope values of parasites encapsulated in the liver by changing the dietary source of the host. We also report variability in isotopic turnover rates between tissues, elements and between infected and parasite-free individuals. These results contribute to our understanding of data obtained from field and commercial hatcheries; and strongly improve the applicability of the stable isotope method in understanding life-history and trophic ecology of fish populations.
Highlights
The natural abundance of stable isotopes in consumer tissues has been widely used by ecologists to identify dietary components and trophic interactions within food webs [1,2]
Δ15N and δ13C turnover rates were fastest in liver tissue in all fish, followed by blood and muscle (Fig 1A–1F)
Previous findings imply that the metabolic contribution of δ15N and δ13C as elemental turnover rate in liver can reach ca. 90% [17]Overall, δ15N and δ13C turnover was faster in perch liver than in blood and muscle (Fig 1)
Summary
The natural abundance of stable isotopes in consumer tissues has been widely used by ecologists to identify dietary components and trophic interactions within food webs [1,2]. Most stable isotope investigations in vertebrate consumers focus on simplified assays of a single tissue, such as muscle. Such analyses assume that muscle isotope values are a reasonable approximation of consumer isotope values overall. In fish, previous stable isotope analyses of parasitized tissues have indicated, somewhat controversially, that infection alters the allocation of food resources within an individual consumer ([4] and references therein)
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