PLANKTON PRODUCTION IN PISH PONDS 
167 
It was more abundant in June than during any other month, with the maximum of 
904 individuals per liter occurring on June 9. Ceriodaphnia was present once in 
May, once in June, once in July, and once in August. In September it occurred in 
2 samples. The maximum of 48 per liter occurred on September 29. Chydorus was 
present throughout May and September. It was present also in the first June sample 
and in one of the August samples. The maximum of 66 per liter occurred on June 9. 
Daphnia did not occur until June 9, but after that date it was always present save 
for the one exception on September 9. It was more abundant during July and 
August than during June and September. The maximum of 297.5 per liter oc- 
curred on August 18. Diaphanasoma occurred once in May and July. During 
June it was absent and during August and September it was always present. The 
maximum of 13 individuals per liter occurred on September 19. The Rotifers were 
represented by the following genera: Anuraea, Asplanchna, Brachionus, Cathypna, 
Polyarthra, Rotifer, and Triartlira. Of these Anuraea was present the greatest 
number of times. It was most abundant in May and June and was absent during 
September. The maximum number per liter was 134.2, which were found in the 
sample taken on May 29. Asplanchua occurred twice; namely, on May 9 and May 
29. On this latter date 365.2 individuals per liter were present. Brachionus occurred 
once in small numbers. Cathypna was present in small numbers at three different 
times — in May, June, and in September. Polyarthra occurred regularly in May 
and in the first June sample, and after that it occurred in the August 29 samples. 
Thirty-three individuals per liter was the maximum for this genus. Rotifer was 
present in 4 samples scattered over the entire season. The maximum number per 
liter was only 1.7. Triarthra occurred in small numbers in 2 of the May samples. 
In the first June sample 38 individuals per liter were present, but it was absent from 
the rest of the samples. 
Centrifuge plankton . — In the centrifuge plankton all the algae have been enumer- 
ated, but only the genera that were fairly common will be mentioned here. Of the 
Myxophyceae, Anabaena and Aphanizomenon deserve mention. Anabaena was 
present in the 3 samples from May 29 to June 30, inclusive. The numbers of fila- 
ments per liter present were as follows: May 29, 4,680,000; June 9, 6,345,000; and 
June 20, 3,600. Aphanizomenon made its first appearance on May 19, when 6,500 
filaments per liter of water were present. On May 19 this number had risen to 
3,025,000 and on June 9 to 4,635,000. On June 20 it was down to 396,000 per liter, 
but it rose again to 1,670,400 on June 30. After this date it occurred in small numbers 
only. Among the Chlorophycese, Gloeocystis, and Oocystis may be mentioned. 
Gloeocystis occurred in small numbers in 2 of the June samples. It was present 
regularly from July 20 to September 8, the maximum of 93,600 per liter occurring on 
the last-mentioned date. Oocystis was present to the extent of 252,000 individuals on 
May 29 and 409,600 on June 9. After that it occurred fairly regularly but only in 
insignificant numbers. Of the diatoms, Synedra is the only form that occurred with 
any degree of regularity and was most abundant during May, with the maximum of 
122,200 cells per liter occurring on May 9. Of the Peridinise, the genus Ceratium 
was the most common. This form was, except for 1 sample, always present after 
the end of June. The maximum for Ceratium was 28,800 cells per liter and occurred 
on August 29. 
