From SARC http://srac.tamu.edu/index.cfm?catid=25 Algae Blooms in Commercial Fish Production Pond

See also SARC Fertilization of Fish Ponds http://srac.tamu.edu/index.cfm?catid=25



Important primary components of

the ecosystem in a fish production

pond are the microscopic algae, or

phytoplankton. Suspended in the

water, these microscopic, singlecelled

plants are often collectively

referred to as the �bloom.� Like all

green plants, phytoplankton

produce oxygen during the

daylight hours as a by-product of

photosynthesis. This is a major

source of oxygen in fish pond

waters.

Blooms are also responsible for

consuming much of the oxygen

produced. Fortunately, during

daylight they usually produce

more oxygen than they use,

resulting in a surplus for fish and

other organisms. At night or in

cloudy weather, however, production

of oxygen through photosynthesis

ceases or is greatly reduced,

but the consumption rate does not

change, often resulting in a deficit

in the oxygen �budget.� Under

certain conditions, the level of

oxygen can become critically low

and fish may suffocate or at least

become stressed to the point of

being susceptible to disease.

Phytoplankton blooms also serve

the useful purpose of shading the

pond bottom, thus preventing

growth of aquatic weeds. Uncontrolled

weed growth can prevent

fish producers from effectively

seining their ponds.

The pond community

The two most common types of

algae found in blooms belong to

the green and blue-green families.

While green algae generally

dominate cool weather blooms,

blue-green algae usually account

for as much as 50 to 75 percent of a

bloom in the summertime. Once

blooms become dense enough to

significantly reduce sunlight

penetration, conditions favor

growth and development of the

blue-green groups of algae. Bluegreen

algae are often associated

with off-flavor problems in either

of two ways. Some blue-green

algae produce substances called

geosmin and MIB (methylisoborneal),

which impart undesirable

flavors in fish. Additionally, when

weather conditions or other factors

stress the algae and they begin to

die off in large numbers, off-flavor

compounds are produced by the

decomposition process.

A complex community of microscopic

animals is also typically

associated with a phytoplankton

bloom (Figure 1). Most of these

tiny animals, referred to as zooplankton,

are herbivores that graze

on the phytoplankton �pasture.�

As a major food item for small fish

in natural aquatic habitats, zooplankton

provide a link between

the bloom and the rest of the food

chain. Apart from the zooplankton

and the fish being cultured, most

of the other animal life present can

be found on and in the pond

bottom. A typical pond bottom

community includes bacteria,

protozoans, insect larvae, true

worms, crustaceans, snails and

other animals in varying proportions.

These organisms survive by

feeding on or breaking down fish

wastes and any uneaten feed that

reach the pond bottom.