Media type: E-Article Title: A noninvasive method to determine fat content in small fish based on swim bladder size estimation Contributor: Kotrschal, Alexander; Fischer, Barbara; Taborsky, Barbara imprint: Wiley, 2011 Published in: Journal of Experimental Zoology Part A: Ecological Genetics and Physiology, 315A (2011) 7, Seite 408-415 Language: English DOI: 10.1002/jez.686 ISSN: 1932-5223; 1932-5231 Origination: Footnote: Description: <jats:title>Abstract</jats:title><jats:p>The presence of fat stores in fish is widely used as a correlate of fish health and fitness. Techniques to measure fat content with some accuracy are available for medium‐sized and large fish, but apart from morphometric indices, a noninvasive method to determine fat content in small fish has hitherto been lacking. In this study, we introduce a novel method to measure the fat content in live fish that can be applied also to small fish of less than 0.5 g of body mass. This approach relies on a precise measurement of the swim bladder volume, from which fat content can subsequently be deduced. As fat is positively buoyant, fish with larger fat stores require a smaller swim bladder to attain neutral buoyancy. To determine swim bladder volume, we developed a measuring device, which makes use of the differential compressibility of air and water. A fish is placed in a pressure‐tight chamber to which a standardized amount of water is added. The resulting change in pressure Δ<jats:italic>p</jats:italic> is inversely proportional to the volume of the swim bladder. Using juveniles and adults of <jats:italic>Simochromis pleurospilus</jats:italic> (Nelissen, <jats:ext-link xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="#bib25">'78</jats:ext-link>; Pisces: <jats:italic>Tropheini</jats:italic>) a small cichlid fish, we show that Δ<jats:italic>p</jats:italic> is tightly related to structural size, mass, and body condition. Most importantly, this approach allows to predict the visceral fat content of small fish more precisely than the six most commonly used morphometric body indices. <jats:italic>J. Exp. Zool. 315:408–415, 2011</jats:italic>. © 2011 Wiley‐Liss, Inc.</jats:p>