PLANKTON PRODUCTION IN FISH PONDS 
163 
PLANKTON 
Net plankton . — The net plankton was usually low. The maximum amount pres- 
ent in 10 liters of water was 0.25 cubic centimeter. The average for 15 determina- 
tions was 0.11 cubic centimeter per 10 liters of water. The zooplankton counts 
made on the net plankton samples are here summarized very briefly. Cyclops was 
present in all save 2 samples. The maximum of 64.7 individuals occurred on May 9. 
On the average Cyclops were most abundant in August. Diaptomus was present 
in small numbers 5.25 per liter on June 20. Then it was present regularly from July 
28 to September 29. The maximum number per liter was 9.0. This number was 
present on August 29. Nauplii were always present. They were most abundant in 
August. The maximum of 142.5 per liter occurred on August 8. Bosmina was 
present fairly regularly. The maximum of 212.5 individuals per liter occurred on 
June 9. Ceriodaphnia was present at four different times, but only in very small 
numbers. Chydorous occurred in 1 sample each for the months of June, July, and 
August and in 2 samples in September. The maximum of 13.6 per liter was reached in 
June. From May 29 on, Daphnia occurred more or less regularly. The maximum of 
115.5 individuals per liter occurred on May 29. Diaphanasoma was present several 
times, but only in very small numbers. Of the Rotifera, the genus Anuraea was 
always present. The maximum of 155.2 per liter occurred on June 20. Brachionus 
was present twice in small numbers. Asplanchna occurred in 5 samples, reaching a 
maximum of 33 per liter on May 29. Cathypna occurred at six different times in 
small numbers. Polyarthra was also present in 6 samples, the maximum of 11.4 per 
liter coming in September. Triarthra occurred twice in May and once in June. In 
the June sample 17.0 individuals per liter occurred. The genera Rotifer, Noteus, and 
Monostyla occurred each once in insignificant numbers. 
Centrifuge plankton . — All the algse in the centrifuge plankton have been enumer- 
ated, but only the numerically important ones are discussed here. Among the 
Myxophyceae, Aphanizomenon may be mentioned. This alga was present fairly 
regularly after June 9, but it never occurred in large numbers, the maximum being 
16,400 filaments to the liter. This number occurred in the sample for July 20. 
These small numbers are in marked contrast to the large numbers for Aphanizomenon 
in D 9. Anabaena, which also was very abundant in D 9, was absent altogether 
from D 5. Of the Chlorophyceae, Gloeocystis and Pandorina may be mentioned. 
Gloeocystis occurred in insignificant numbers on June 20. On August 29 and Sep- 
tember 8, 18,000 and 72,000 cells per liter, respectively, were present. Pandorina 
occurred in a majority of the samples after June 20. The maximum of 28,800 
colonies per liter occurred on June 30. Synedra, the only diatom that needs to be 
mentioned, was present in relatively small numbers in all samples save one. The 
maximum of 104,400 cells per liter occurred on August 8. On May 9, 66,300 cells 
per liter were present. Of the Flagellata, Euglena was present in 6 samples. The 
maximum of 20,700 was found in the sample for August 8. 
POND D 9 
D 9 had been stocked with fish in the fall of 1926 and was not drained in the 
spring of 1927. Like D 4, it was fertilized with a 3:1 mixture of sheep manure and 
superphosphate. On April 26 and on June 17, 81 pounds of this mixture were added 
to the pond. Then from July 2 until August 23, 27 pounds were added at 5-day 
intervals. 
