Using stable isotope analysis to assess the relationship among dietary protein sources, growth, nutrient turnover and incorporation in Nile tilapia ( Oreochromis niloticus )

Abstract

Nile tilapia (1.20 g) were fed for 56 days in five treatments (FM100 containing only fish meal [FM] as a protein source; soybean meal (SBM) replace 25%, 50%, 75% and 100% of FM protein in the diets of FM75, FM50, FM25 and FM0, respectively) to assess the effects of dietary protein sources on growth, turnover half‐life of nitrogen and carbon stable isotopes (δ13C and δ15N) in muscle, isotope discrimination factors (Δ15N and Δ13C), and the relative contribution of protein sources to muscle growth. Results showed that the final body weight, weight gain and specific growth rate of fish fed diet FM25 were significantly higher than other treatments (p < .05). By day 35, fish under all treatments reached isotopic equilibrium, and the equilibrium values consistently increase as a function of stable isotope values in diets. Growth accounted for most isotopic changes in muscle and resulted in significantly shorter half‐lives of nitrogen and carbon in FM25 (p < .05). The Δ15N of FM25 and Δ13C of FM0 were significantly lower than other treatments (p < .05). The proportional contributions of SBM protein were significantly higher than their respective levels in FM75 and FM25 (p < .05), indicating a preferential incorporation of nitrogen from the SBM in muscle tissue.

Isotopic techniques in aquaculture nutrition: State of the art and future perspectives

“…That is, the heavy isotopic forms (for nitrogen and carbon, 13 C and 15 N) are preferentially retained in tissues, while the light isotopic forms ( 12 C, 14 N) are excreted. 6 This metabolic effect leads to isotopic differences between animal consumers and their respective diets (isotopic discrimination factors, IDFs).…”

“…These isotopic differences can be natural or manipulated. For example, in micro-and macroalgae, it has been shown that the isotopic values of carbon and nitrogen ( 13 C/ 12 C and 15 N/ 14 N, respectively, expressed in delta notation as δ 13 C and δ 15 N, Table 1) can be manipulated by specific culture media (nitrogen) and through the use of supplementary CO 2 (carbon). 8,9 Once a 'desired' isotopic value has been reached, for example, in microalgae, the biomass can be used to modify the isotopic values of zooplankton, and this, in turn, can be fed to larval organisms to trace nutrients and/ or to quantify contributions of dietary items to growth.…”

“…The employment of SIA to estimate assimilation allows obtaining an additional physiological indicator to characterize the nutritional suitability of traditional and emergent alternative ingredients. Similar isotopic methods have been applied in aquaculture organisms as diverse as fish, 15 crustaceans 3 and echinoderms. 16 By analysing the isotopic values of feeding items and consuming animals, inferences on prey/feed use can be drawn, trophic relationships can be better defined and the physiological readiness to use nutrients can be established, a particularly useful aspect in the larviculture of marine organisms.…”

“…The isotopic techniques, in conjunction with the estimation of traditional growth parameters, can assist in the design of improved feeding protocols and also in formulating suitable compound feeds suitable for the animal's biological stage and type of grow-out system. Joyce and Pirozzi 88 conducted a study on another Australian freshwater crayfish species (Cherax quadricarinatus), where δ 13 C and δ 15 N values of crayfish and potential food sources were evaluated in different farms. Authors concluded that the contribution of natural feeding items to growth varied among four sampled farms due to type of feed supplied (raw corn, lupin, soybean, and chicken feed) and availability of natural sources.…”

“…values of AA in microalgae Tetraselmis suecica and rotifers fed on the former. Authors observed differences in the δ15 N values of some AA after their transference from microalgae to rotifers, while other AA showed little or no change. The authors found that such patterns in the IDFs varied substantially and defined two categories.…”