Stable isotope signatures and trophic-step fractionation factors of fish tissues collected as non-lethal surrogates of dorsal muscle

Abstract

Scales and fin tissue are strong surrogates of dorsal muscle in food web studies as they can provide estimates of muscle values within an acceptable level of error when species-specific methods are used. Their derived fractionation factors can also be applied to models predicting fish diet composition from δ(15) N and δ(13) C values.

High variability in stable isotope diet-tissue discrimination factors of two omnivorous freshwater fishes in controlled ex situ conditions

“…The three diets used in the experiment were all based on pelletized feeds; these were preferred to natural foods given that the experiment was based on exposing the species to these diets over a set time period and thus variability in the stable isotope values of the feeds would vary little through use of single, homogeneous batches, and arguably less than if natural food sources were utilized (Busst et al, 2015). They also enabled fish to be exposed to set levels of the food over the course of the experiment.…”

“…The second diet was 'Wheatgerm pellets', hereafter referred to as 'wheatgerm', comprising 20% protein, 6% fat (as oil), 2.5% crude fibre and 2.5% ash, and whose base ingredient was plant based (Nishikoi Aquaculture, available from http://www.nishikoi.com/pond-food/nishikoi-wheatgerm, last accessed 28 October 2015). The third diet was crushed pelletized fishmeal, referred to here as 'fishmeal', comprising 45% protein, 10% fat, 1.4% crude fibre and 5.8% ash, and whose base ingredient was marine fish (Busst et al, 2015). Note that data for the fishmeal diet were generated in a previous experiment (Busst et al, 2015) and this was not repeated here to avoid unnecessary use of live fish in experiments.…”

“…This general application of constant discrimination factors across consumers within mixing models is potentially problematic, as studies increasingly suggest they can vary between species, ages, diet compositions, body sizes, sample preparations and tissue types (Locke et al, 2013;Brush et al, 2012;Busst et al, 2015). The commonly cited values of 3.4±0.98‰ for δ 15 N and 0.39±1.3‰ for δ 13 C (DeNiro and Epstein, 1981;Minagawa and Wada, 1984;Post, 2002) could thus be inappropriate for use in many models, resulting in dietary predictions whose variability within and between species could be due more to inappropriate discrimination factors than actual dietary variation (Busst et al, 2015).…”

“…The commonly cited values of 3.4±0.98‰ for δ 15 N and 0.39±1.3‰ for δ 13 C (DeNiro and Epstein, 1981;Minagawa and Wada, 1984;Post, 2002) could thus be inappropriate for use in many models, resulting in dietary predictions whose variability within and between species could be due more to inappropriate discrimination factors than actual dietary variation (Busst et al, 2015). The specific food items that contribute to the overall diet of a consumer can substantially influence their stable isotope discrimination factors (Caut et al, 2008).…”

Tissue-specific turnover rates of the nitrogen stable isotope as functions of time and growth in a cyprinid fish

“…Consumer tissues tend to be considered at equilibrium with their diet after 4-5 halflives (Hobson & Clark, 1992). Increasingly, the sampling of tissues for stable isotope analysis utilises the non-invasive or non-destructive sampling of tissues, such as using fin tissue and scales rather than dorsal muscle for fishes (Busst et al, 2015;Busst & Britton, 2016;Vašek et al, 2017). Knowledge on the turnover rates of these tissues is often missing, leading to problems in their application to ecological studies (Busst & Britton, 2016).…”