Depression Periods in Cladocera

For more than 3 years the writer has been interested in the periodic depressions that so frequently occur in stock cultures of Cladocera reared in manure infusions. Such periods have been reported by Warren, 1 Hartman, 2 and Allee. 3 Stuart, Cooper and Coady 4 believed that no one environmental factor was responsible for their occurrence and suggested several factors that might be associated with the phenomenon. Since Allee 3 has so clearly shown the detrimental effects of unconditioned water on aquatic animals it occurred to the writer that this factor might play some role in depression periods in Cladocera.

Accordingly, during a part of the summer of 1931 when stock animals showed continued depression periods the pond water employed in the preparation of medium for these animals was treated in the following way. Five gallons of the raw water was filtered through paper and together with a suitable quantity of garden soil was put into an aquarium. A few hours later, after sedimentation of the gross silt, the aquarium was stocked with 100 or more adult Cladoceran mothers (Moina macrocopa). In each of 6 separate experiments many of these animals died within 12 to 18 hours, and a similar number of mothers with eggs or embryos present in the brood chamber were added to the aquarium. For the most part these animals survived and released their young. The water was arbitrarily held to be conditioned in from 48 to 72 hours when a slight opalescence or turbidity appeared: this opalescence was shown by bacteriological counts to be due to the increased number of bacteria. The water was then filtered through paper and used for diluting a portion of the concentrated manure infusion employed for rearing these animals. 5