Heterogeneity in food-web interactions of fish in the Mwanza Gulf, Lake Victoria: a quantitative stable isotope study

Stomach contents and stable isotopes confirm ontogenetic diet shifts of Nile perch, Lates niloticus, in southern Lake Victoria

“…It can be explained by the difference in timespan-coverage between isotopes and stomach contents (hours in the case of stomach contents and months in the case of stable isotopes), by diel feeding behaviour of Nile perch and by immigration of Nile perch from other parts of the lake into the Gulf (Cornelissen et al, 2017). Furthermore, variation in assimilation of N between types of prey, resulting in diet-source specific enrichments between trophic transfers (McCutchan et al, 2003), and the large isotopic variation within prey sources (Cornelissen et al, 2017) may also explain differences between estimated diets based on stable isotopes and stomach contents. This highlights the limits of both stable isotopes and stomach contents to estimate trophic interactions between predator and prey and the importance of using stomach contents to verify and select diets in stable isotope mixing models.…”

“…All stations were sampled in each season, except for station 6, which was not sampled during the dry season. For stable isotopes, fish and invertebrates were collected according to Cornelissen et al (2017). Fish <5 cm standard length (SL) were skinned and filleted whole.…”

“…Samples were preserved in 70% ethanol and stored at -20°C. The processing and laboratory analyses of stable isotopes were performed according to Cornelissen et al (2017). The isotope ratios were measured against reference standards of carbon and nitrogen by using USGS40 L-glutamic Acid C5H9NO4, with δ 15 N of −4.5‰ and δ 13 C of −26.389‰ (SDs were 0.13 and 0.11 for δ 13 C and δ 15 N values, respectively).…”

“…where R = 13 CO2: 12 CO2 or R = 15 N2: 14 N2. δ 13 C values were corrected for lipid contents (Cornelissen et al, 2017;Post et al, 2007). Diets of Nile perch <5 cm SL were analysed by dissecting the stomachs.…”

“…Monthly weather conditions during the study period from 2009 to 2011 of mean temperature (upper squares), rainfall (histograms) and mean wind speed (lower squares) ( Fig. S1, Cornelissen et al, 2017).…”