10 UNIVERSITY OF WISCONSIN STUDIES 



shows the temperatures and the gaseous contents of the water 

 at various depths. The lower temperature of the deeper water, 

 with the decrease in oxygen and increase in carbon-dioxide, 

 indicates a stratified condition. However, there was an abun- 

 dance of oxygen for fishes at all depths. A Secchi disc 20 cm. 

 in diameter at 10:45 A.M. in bright sunlight disappeared at 

 3.5 meters, July 18. 



Catches with fine (18 mesh per cm.) and coarse (10 mesh) 

 tow nets in deep and in shallow water indicated that plankton 

 was not very abundant. Practically nothing was caught in 

 the coarse net; the fine one yielded some Diaptomus, Cyclops, 

 considerable numbers of Moinodaphnia, and a few algae. 



Hauls with Juday's (1916) improved Ekman mud dredge 

 were more productive of results. The dredge used was of 

 brass and cubical in form. It took samples of the bottom to 

 a depth of 15 cm. over an area 15X15 cm. Table II gives the 

 results of ten hauls made at various depths on July 18. It will 

 be seen that the midge larvae, so characteristic in temperate 

 regions of deep lakes with muddy bottoms, are largely replaced 

 by snails. Most of the snails were of small size and the catches 

 after they had been freed from mud consisted largely of 

 "dead" snail shells. A young eel (Symbranchus marmoratus) 

 caught at a depth of fifteen meters was placed in a bottle with 

 bottom mud and water. It at once burrowed into the mud 

 but in a few minutes protruded its head and kept it out. On 

 July 25 thirty hauls were made with the dredge where the water 

 was 14.2 M. deep and another small eel was thus secured. A 

 thorough study of the bottom of Lake Valencia would doubtless 

 add to the known fauna, but the data presented in Table II is 

 indicative of the general conditions. It will be noticed that 

 snails are very abundant in deep water. Systematic and 

 extensive use of a mud dredge in the lake would doubtless give 

 interesting results relating to the ecological distribution of the 

 different species. 



Reviewing the conditions afforded by Lake Valencia as an 

 environment for fishes it may be said to be a tropical lake with 

 muddy bottom and receding shore line. The water is of average 

 turbidity and hardness. Distinctive habitats are the muddy 

 bottom in deep water; the sandy, pebbly, and rocky shores 

 of the islands; the rush-grown shores about the margin of the 

 lake, and the mouths of rivers where emergent plants other than 

 rushes are found. 



