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 1Each 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 |
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.
Based on the results of Experiment 1, if Experiment 2 were repeated except that all the A. percula were fed Diet R, would the average SGRs more likely have been lower or higher for each group?
Correct answer: C
Explanation
A. Incorrect. The description of Experiment 2 indicates that all fish were fed Diet T. The SGR for Diet T was 0.35 percent/day while the SGR for Diet R was 0.40 percent/day, which is 0.05 percent/day greater, not less, than the SGR for Diet T. Based on this information, if Experiment 2 were repeated but all the A. percula were fed Diet R, the average SGRs would more likely be higher, not lower.
B. Incorrect. The description of Experiment 2 indicates that all fish were fed Diet T. The SGR for Diet T was 0.35 percent/day while the SGR for Diet R was 0.40 percent/day, which is 0.05 percent/day greater, not 0.10 percent/day less, than the SGR for Diet T. Based on this information, if Experiment 2 were repeated but all the A. percula were fed Diet R, the average SGRs would more likely be higher, not lower.
C. Correct. The description of Experiment 2 indicates that all fish were fed Diet T. The results of Experiment 1 in Table 1 show that the SGR for Diet T was 0.35 percent/day while the SGR for Diet R was 0.40 percent/day, which is 0.05 percent/day greater than the SGR for Diet T. Based on this information, if Experiment 2 were repeated but all the A. percula were fed Diet R, the average SGRs would more likely be higher.
D. Incorrect. The description of Experiment 2 indicates that all fish were fed Diet T. The SGR for Diet T was 0.35 percent/day while the SGR for Diet R was 0.40 percent/day, which is 0.05 percent/day greater than the SGR for Diet T, not 0.10 percent greater.
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