202

The positive square term on the equation accounts for the

decrease in frequency of larger fish at highest densities,

an observed phenomenon believed to have been caused by

differential selection, or the selection of larger

individuals by predators, which fed most efficiently at

high densities.



Other Small Forage Fish

 Mosquitofish made up 87% of the dry weight of fish in

their size group. Other similar-size fish species were

relatively unimportant in the samples. Heterandria formosa

was the second most abundant. Lucania goodei was the only

fish of this size group which occurred frequently in

samples from the open pond.



Crayfish

 The standing stock of crayfish in Corkscrew -marsh grew

from 0.06 g/sq-m on July 9 to 5.87 g/sq-m on October 22,

declining thereafter. The maximum standing stock of

crayfish was approximately 14 times the maximum standing

stock of Mosquitofish prior to the concentration of

Mosquitofish. Crayfish were completely absent from samples

taken in the pond during March, April, and June, 1975, but

reoccurred in samples from the zone of emergent vegetation

at the edge of the pond in August and September. The

calculated rate of crayfish production, "r" in equation 19