Sample lab report
Johnny B. Goode
The effect of body size on metabolic rate in the goldfish (Carassius auratus).
Introduction
The effect of body size on energy metabolism determines many aspects of an animal's life
history. For example, small animals generally have higher mass-specific metabolic rates than large
animals. As a result, small animals must eat relatively more per day than larger animals and have to
spend more time searching for food. Such scaling effects have been demonstrated for a wide variety of
animals (Calder, 1984). The causes of this allometric effect are a matter of intense debate. Information
on additonal taxa are likely to shed light on the phenomenon. Data for fish are relatively incomplete.
Goldfish (Carassius auratus) are suitable for such laboratory studies because they are available in a
variety of sizes and are tolerant of very low levels of dissolved oxygen. The purpose of this experiment
is to determine the effect of body size on oxygen consumption in goldfish.
Materials and Methods
Goldfish were obtained from a local pet store. Individuals were weighed, body length
measured, and placed in sealed jars of 0.5-L volume for one hour. The temperature of the water was
held constant (25oC) by placing the jars in an upright incubator. At the 30-minute mark respiratory rate
was determined by counting the number of bucal-opercular movements during a 30-s interval. The
oxygen concentration was measured before and afterward using the Winkler titration. Oxygen
consumption (MO2) was calculated accordingly. Class results were pooled and recorded.
Results
Our fish was somewhat active during the experiment, as were those of other students. Fish
were of typical size, and maintained normal respiratory rates during the measurements (Table 1).
Table 1. Characteristics of goldfish used in the study.
Average
N
Body mass (g)
6.1
7
Body length (cm)
9.5
7
Oxygen consumption (mg/g
2.5
7
h)
Respiratory rate (/min)
101
6
Larger fish consumed more oxygen than smaller fish; therefore, total oxygen consumption
increased with increasing body mass. However, mass-specific MO 2 was greater in smaller fish than
larger fish. The pooled MO2 data were plotted as a log-log function of body mass (M b). Log MO2
decreased linearly with increasing log M b (Figure 1). A least squares regression performed on the data
yielded the following equation: MO 2 (ml/g.min) = 1.4Mb-0.25 (r2 = 0.85).
Figure 1. The effect of body mass on oxygen consumption in the goldfish.
Discussion
Our exponent was -0.25, which is commonly observed in numerous taxa (Calder, 1984). As
size increases, mass increases with length 3, while surface area increases only with length 2. Hence, an
exponent of 2/3 or .67 is predicted. If oxygen consumption per unit surface area is constant, then the
exponent of our equation should be -0.33; hence, the surface area hypothesis is not supported. Our
result is essentially the same as that predicted by demands of physical support and muscle biophysics
(McMahon, 1973), which seems paradoxical since aquatic organisms are supported by the bouyancy of
water.
Total oxygen consumption increased with increasing body mass; however, mass-specific
oxygen consumption decreased with increasing body mass. Though the exact causes of this relationship
remain unknown, its pervasive effects are well understood. A larger goldfish uses more total energy per
unit time. Smaller goldfish must, therefore, eat a greater proportion of their body mass as food, and
probably must spend more time acquiring food. This relationship holds true for a diversity of groups of
organisms, including insects, mammals and birds (Lasiewski and Dawson, 1967; Stahl, 1967; Coelho
and Moore, 1988).
Literature Cited
Calder, W.A.III. 1984. Size, function, and life history. Harvard
University Press, Cambridge Massachussetts, 431 pp.
Coelho, J.R. and A.J. Moore. 1988. Allometry of resting metabolic
rate in cockroaches. Comparative Biochemistry and Physiology
94A:587-590.
Stahl, W.R. 1967. Scaling of respiratory variables in mammals.
Respiratory Physiology 22:453-460.
Lasiewski, R.C. and W.R. Dawson. 1967. A re-examination of the
relation between standard metabolic rate and body weight in birds.
Condor 69:13-23.