Naturally-occurring stable isotopes as direct measures of larval feeding efficiency, nutrient incorporation and turnover

Abstract

Stable isotopes are non-hazardous markers that have been widely-used in assessing energy flow within aquatic ecosystems. Hatchery systems are also highly amenable to this approach, as they represent controlled mesocosms with a limited number of food sources and short planktonic food chains with rapid and measurable bioaccumulation of the heavier stable isotopes of carbon and nitrogen at each trophic step. Differences in the natural isotopic composition of dietary components may be used to provide direct integrated measures of ingestion, nutrient incorporation and growth through development under normal feeding and environmental conditions, in either the laboratory or the hatchery. Simple isotopic mixing models allow estimation of relative utilisation of inert diets and live feeds, and individual components of compound feeds. Such experiments have investigated the effectiveness of cofeeding regimes, optimal timing of live food transitions (eg from rotifers to Artemia), presentation of inert diets, optimal size/age for weaning and incorporation of specific dietary components. Furthermore, time-series measurement of changes in tissue isotopic signature (δ 15 N, δ 13 C) enables modelling of growth dilution and tissue turnover components of isotopic change driven by nutritional sources. These measures need to take into account the difference in isotope values that is typically observed between the diet and consumer (isotopic discrimination factor, ∆). In marine larvae and early post-larvae, ∆ 13 C and ∆ 15 N have been found to range widely, from 0.4-4.1‰ and 0.1-5.3‰ respectively. The observation of such a high level of variation within species and life stages indicates a strong effect of diet quality on isotopic discrimination. Elucidating mechanisms underlying such observations, and much greater resolution in larval nutritional studies, can be achieved by application of rapidlydeveloping techniques for compound specific stable isotope analysis in tracing the transfer of dietary sources of carbon and nitrogen into tissue components. Fast growing aquatic larvae represent excellent model organisms exhibiting rapid transitions in isotopic composition in 3 response to diet, rapidly changing feeding behaviour and transitions in trophic level with ready ingestion of modifiable experimental diets in short and controlled food chains. Thus results of studies of the effects of diet composition, developmental stage, growth rates or environmental conditions on stable isotope incorporation will be of broad relevance not only in terms of larval nutrition but can also more broadly inform the design and interpretation of ecological studies.

Isotopic half‐life and enrichment factor in two species of European freshwater fish larvae: an experimental approach

“…Although TEFs are commonly used by scientists for quantifying the contribution of alimentary sources to the diet of consumers, they vary greatly according to the considered element and sample tissue, as well as the physiology of the studied species . A meta‐analysis by Le Vay and Gamboa‐Delgado reported a considerable variability in aquatic larvae and post‐larvae Δ 13 C and Δ 15 N observed under laboratory conditions: from 0.4 to 4.1 ‰ for carbon and from 0.1 to 5.3 ‰ for nitrogen. The TEFs gathered in this meta‐analysis come from various organisms, mainly crustacean larvae.…”

“…larval growth phase) and their taxonomic proximity. TEFs observed between consumers were higher in the literature for the same type of diet; e.g., the Δ 15 N of marine crustaceans fed with Artemia varied between 0.1 and 2.5 ‰ . For both consumers, we also noticed that the variation in Δ 13 C was higher than in Δ 15 N in this study (contrary to the literature) and depended mainly on the type of diet (Table ): Δ 13 C differences were 1.8 to 2.4 ‰ greater for Artemia sp.…”

Isotopic discrimination factors and nitrogen turnover rates in reared Atlantic bluefin tuna larvae (<em>Thunnus thynnus</em>): effects of maternal transmission

“…Tissues of fast-growing animals exhibit shorter half-times (t 50 ) for nitrogen than slow-growing animals (MacAvoy et al 2005), due to the fast growth rates characteristic of early life stages. The nitrogen isotopic changes observed in larvae can be attributed to tissue accretion and not to tissue metabolic turnover, contrary to what has been observed in adult organisms (Martínez del Río et al 2009, Le Vay andGamboa-Delgado 2011).…”

A comparative study on growth, protein turnover and energy budget of green and white color morphs of sea cucumber Apostichopus japonicus (Selenka)

“…Sea cucumber generally requires a relatively low energy supply for optimum growth (Sun et al 2004, Zhu et al 2005. Stable isotope analysis can effectively yield valuable information on the incorporation of micro-and macronutrients (Le Vay & Gamboa-Delgado 2011, MartinPerez et al 2013, Xia et al 2015b. In the present study, we compared the discrepancies of growth, protein turnover and energy budget of green and white sea cucumber under different dietary regimes, to provide scientific basis for further study on the physiological ecology and nutriology of sea cucumber.…”