Application of stable δ13C and δ15N isotope analysis for trophic levels discrimination of fish species in Daduru Oya reservoir; Sri Lanka

Abstract

Stable isotopes vary the rate of reaction and incorporation into biological structures and there are a range of exciting applications of stable isotopes in food chain studies. This ratio of 13C to 12C provides information on the primary energy source, while isotopes ratio of 15N to 14N trophic levels. This approach is used to discriminate the tropic levels of 4 exotic and 16 native fish species sampled from the Daduru oya reservoir using dorsal muscle tissues. Samples were freeze dried at -40 0C. Dried samples were packed in Tin (Sn) Capsule. δ13C and δ15N were measured using Isotope Ratio Mass Spectrometry (IRMS). Gut content analysis was done parallelly. Primary consumers were represented by detritivores including Cirrhinus mrigala and Labeo dussumieri with mean δ15N values of 5.73 to 7.15‰ and δ13C values of -31.23 to -32.31‰. The sample was dominated by omnivores with a mean of δ15N value of 9.5 to 13.4% and a mean of δ13C -26.8 to -32.6%, those had a diet with significant contribution of insects, crustaceans and fish parts. They had ranged their δ15N value from 11.96 to 13.4 and δ13C value from -26.88 to -29.42‰. This group include species from the genera of Amblypharyngodon, Devario, Esomus, Oreochromis, Pseudetroplus and Puntius. The gut content of Pterygoplichthys sp. and Esomus dandrica consisted of more detritus and some animal bone food items. Their δ15N ranged from 9.83 to 10.28‰ and δ13C ranged from -31.13 to -32.61‰. The carnivore’s isotope signatures were not projected satisfactorily due to the fewer samples. The consumer δ15N values suggested three trophic levels; detritivores, herbivores and omnivores. The dendrogram was created using a final partition of 3 clusters, which occurs at a similarity level of approximately 50. The current analysis reveals that estimates of trophic positions coincide with the trophic fractionation of δ15N 3.4‰ and δ13C 1.0‰ approximately. The study shows the capability of the stable isotopic analysis in tropic level identification of fresh water reservoir fish species.