Answer to Question 1Fish need oxygen to survive (see Figure 17-5 in the lab manual). Unless the water
temperature around the rooted vegetation is too high, small fish should be evident.
Rooted aquatic vegetation also serves as a desirable habitat for many other
organisms, some of which are food for the fish in your sites. The larger fish may only
be active at night or early in the morning in the shallow areas when the dissolved
oxygen content of the water is greatest and pH is the highest at this time (see Figure
17-3 in the lab manual), and the water temperature is lowest.
Answer to Question 2You would expect the shallow water near the rooted plants to be warmer than the
water of the open areas unless you live in a part of North America where the air
temperature is warm during most of the year. In southern Florida, California, and
Texas, the air temperature tends to produce lakes that are permanently stratified
(warmer water on the top and cooler water on the bottom). Thermal stratification
can produce very warm open water areas in a lake. The fish in such a lake will be
confined to the cooler water, which holds more oxygen. The dissolved oxygen and
pH of the water will also vary according to the time of day the samples were taken
(see Figure 17-3 in the lab manual). The dissolved oxygen will vary in different
portions of the lake or pond in relation to the number of aquatic plants, including
algae. Plants tend to increase the oxygen content of the water. The exception arises
when the concentration of algae is so great that they use all the available dissolved
oxygen as rapidly as they produce it.