  Featured Articles  Oxygen Depletion and Other Types of Fish
Kills  04 June 2007  By LSU Ag Center. Although exposure to
agricultural chemicals can occasionally result in direct fish
mortality, most fish kills in recreational and farm ponds are
the result of oxygen depletions.  Dissolved oxygen levels depend
on temperature, pond depth, productivity and fertility, and
water movement. In almost any aquatic environment, fluctuations
in natural nutrient cycles can create imbalances which lead to
oxygen depletions and fish kills. Generally, these fluctuations
are difficult or impossible to predict, but high nutrient levels
from feeding or over-fertilizing almost always compound problems
with oxygen management.  As nutrients accumulate in the pond
system, some end up directly in the bottom mud but most go into
solution in the water column first, where they are used by
plants and animals. The most abundant plants in a well-managed
fishing pond are found in the algal bloom, which gives the pond
water a greenish tint