Measurement of total body composition changes of common carp by computer tomography

Abstract

The crude fat and protein content of the total body was estimated by X-ray computer tomography (CT) and determined by chemical analyses during a feeding experiment with sexually matured common carp. Between 21 and 35 serial scans were taken of altogether 41 fish and samples from the homogenized body were prepared for chemical analyses. Experimental fish with an average body weight of 1453 g originated from a commercial stock of mirror carp. Two feeding regimes (carp feed and carp feed+ad libitum maize) were applied for 57 days and followed by a fasting period of 27 days. Both feeding regimes significantly increased the crude fat content of the whole body that did not decrease during fasting in spite of high water temperature (22°C). No significant changes were observed in crude protein content. The variables used for producing the prediction equations were taken from the density values of the Hounsfield scale, on a range between −90 and +160, by summing the frequencies within each interval of 10 values. Whole body fat content could be estimated with R2=0.89−0.91 accuracy with the principal component analysis using data of all (seven) body regions and only dorsal fin region respectively. Adequate linear regression model could not be calculated by the same procedure for crude protein. Three-dimensional ‘volumetric’ estimation of fat tissue was also carried out on the basis of fat index showing high correlation with measured fat content. The changes of body composition of individual fish can be followed by sequential CT scanning.