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Science Q6
Passage 3 · Science Quiz 3

Amphiprion percula, a species of clownfish, are kept in many home aquariums. Two experiments were conducted to determine how diet and stocking density (number of fish per liter of seawater, fish/L) affect the specific growth rate (SGR; percent increase in length per day, percent/day) in A. percula.

Experiment 1

Each of 12 identical 15 L tanks received 10 L of seawater having a salinity of 33 parts per thousand (ppt), a temperature of 27° degrees C, and a pH of 8.2. Salinity, temperature, and pH were kept constant over the course of the experiment. A. percula of similar lengths were selected, and their lengths were measured, in cm, with a ruler. Then they were equally distributed among the tanks at a stocking density of 1 fish/L. The tanks were then divided equally into 4 groups.

For 4 months, each group was fed a different diet (Diets Q–TQ through T). Each group was fed the same mass of food 3 times daily. At the end of 4 months, the length of each fish was measured, in cm, with a ruler, and the SGR of each fish was calculated. The average SGR was then determined for each group (see Table 1).

Table 1
Diet Average SGR
(percent/day)
Q 0.30
R 0.40
S 0.50
T 0.35
Experiment 2

The procedures for Experiment 1 were repeated except that each group was kept at a different stocking density, 0.5 fish/L, 1 fish/L, 2 fish/L, or 3 fish/L, and all fish were fed Diet T. At the end of 4 months, the average SGR was determined for each group (see Table 2).

Table 2
Stocking density
(fish/L)
Average SGR
(percent/day)
0.5 0.50
1 0.35
2 0.25
3 0.20

Tables adapted from João Chambel et al., “Effect of Stocking Density and Different Diets on Growth of Percula Clownfish, Amphiprion percula (Lacepede, 1802).” ©2015 by Springer.

Which of the following was a dependent variable in Experiment 1?

  1. F

    Volume of seawater in each tank

  2. G

    Specific growth rate

  3. H

    Diet fed to the A. percula

  4. J

    Stocking density of the A. percula

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