Kotrschal Alexander, Fischer Barbara, Taborsky Barbara
Behavioural Ecology, Institute of Ecology and Evolution, University of Bern, Bern, Switzerland.
J Exp Zool A Ecol Genet Physiol. 2011 Aug 1;315(7):408-15. doi: 10.1002/jez.686. Epub 2011 Apr 1.
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 Δp is inversely proportional to the volume of the swim bladder. Using juveniles and adults of Simochromis pleurospilus (Nelissen, '78; Pisces: Tropheini) a small cichlid fish, we show that Δp 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.
鱼类体内脂肪储存情况被广泛用作鱼类健康和体能的一个相关指标。对于中型和大型鱼类，已有一些能较为准确测量脂肪含量的技术，但除了形态测量指标外，此前一直缺乏一种非侵入性方法来测定小鱼的脂肪含量。在本研究中，我们介绍了一种测量活鱼脂肪含量的新方法，该方法也可应用于体重小于0.5克的小鱼。这种方法依赖于对鱼鳔体积的精确测量，随后可据此推断脂肪含量。由于脂肪具有正浮力，脂肪储存量较大的鱼需要较小的鱼鳔来实现中性浮力。为了确定鱼鳔体积，我们开发了一种测量装置，该装置利用了空气和水的压缩性差异。将一条鱼放入一个耐压腔室中，并向其中加入标准化量的水。由此产生的压力变化Δp与鱼鳔体积成反比。使用小鳞丽脂鲤（Nelissen，1978年；鲈形目：丽鱼科）的幼鱼和成鱼，一种小型丽鱼科鱼类，我们表明Δp与结构大小、质量和身体状况密切相关。最重要的是，与六种最常用的形态测量身体指标相比，这种方法能够更精确地预测小鱼的内脏脂肪含量。
