Stable isotopic fractionation in metabolic tissue and otolith organic matrix of tilapia (Oreochromis mossambicus)
Date Issued
2016
Date
2016
Author(s)
Cheng, Li-Chi
Abstract
Otolith isotopic fractionation may differ from other metabolic tissues due to it is metabolically inert calcified tissue. However, lack of knowledge is pronounced for stable isotopic values of otolith organic matrix. In this study tilapia (Oreochromis mossambicus) were fed with five different diets for up to one and half year under controlled conditions, then stable carbon and nitrogen isotope compositions of the metabolic tissues (muscle, liver, gill and scale) and otolith organic matrixes (metabolic inert) were measured by EA-IRMS and GasBench-IRMS, respectively. For the latter, otolith organic matrix had to be converted to N2O by Pseudomonas aureofaciens and P. chlororaphis before the analysis. The results suggested that the minimal mass reqired for the analysis was lower (1/20) for the GasBench-IRMS compared with the conventional EA-IRMS. In addition, isotopic compositions were significantly different between metabolic tissues and the diets. For stable nitrogen isotopic fractionation, muscle and gill had the largest values (3.4-5.6‰), while liver had the lowest values (2.1-3.5‰). For stable carbon isotopic fractionation, scale had the largest values (4.7-6.4‰), while liver had the lowest values (-0.5-0.9‰). Nevertheless, the δ15N compositions were not significantly different between otolith organic matrixes and the diets with the fractionation between -0.5-0.7‰. This result indicated that the source of nitrogen isotope in otolith organic matrix may be directly derived from amino acid without any metabolic transamination. There was no significant correlation among stable isotope values of otolith organic matrixes and somatic weight and standard length. Apart from these, the distribution of N% in otolith also showed similar pattern with crude protein percentage of the dies, except the tilapia fed on eel meal. N% of otolith in other individuals was not correlated to somatic weight and standard length of the fish. We conclude that high temporal resolutions of δ15N profiles analyzed by GasBench-IRMS and N2O can have wide applications, in studying the food sources and trophic shift of the fish at different life stages.
Subjects
otolith organic matrix
metabolic tissue
EA-IRMS
GasBench-IRMS
stable isotopic fractionation
Type
thesis
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