Fish culture in Lakes

Trophic State
Trophic state is defined as the total weight of the biomass in a water body at a specific location and
time. Trophic state is the biological response for nutrient additions to the water bodies
(Nauuman,1929). (Fish culture in Lakes)

The amount of nitrogen, phosphorus and other biological useful nutrients dissolved in the waters
determine the trophic state of the lake. The water trophic is used to estimate its biological condition.
Classification of lakes based on trophic state.The classical and most commonly used method is base d on the productivity of the water body is the biom ass related trophic state index developed by Carlson(1977). Carlson’s Trophic State Index (TSI) is a common method for characterizing a lake’s trophic state or overall health. Carlson’s trophic state index mainly uses algal bio mass involving three variables namely chlorophyll.a (CA), Secchi disc depth (SD) and total phosphorus (TP). Fish culture in Lakes
The trophic state of the lake is classified into three namely – Oligotrophic, Mesotrophic, and
Eutrophic Lakes. When the lake has higher trophic indices may be considered as hyperoligotrophic
or hypereutrophic. (Fish culture in Lakes)

Oligotrophic lake

An oligotrophic lake is one which has a relatively low productivity due to the low nutrient content
in the lake. The waters of these lakes are usually quite clear due to the limited growth of algae in the
lake. The waters of such lakes are of high-drinking quality. Such lakes support aquatic species who
require well-oxygenated, cold waters such as lake trout. Oligotrophic lakes are usually found in the
cold regions of the world where mixing of nutrients is rare and slow due to the low temperatures of
the lake waters. Fish culture in Lakes

Mesotrophic lake

Lakes with an intermediate level of productivity are called mesotrophic lakes. These
lakes have medium-level nutrients and are usually clear water with submerged aquatic plants.

Fish culture in Lakes

Eutrophic lake

Eutrophic Lakes have high levels of biological productivity and this lake support an
abundance of plants due to the rich nutrient constitution, especially nitrogen and phosphorus.
Initially, eutrophic lakes accelerate multiplication and growth of Lake Fauna due to the high
levels of oxygen provided by a large number of plants growing in the lake. However, when
things cross limits, plants or algal blooms overcrowd the lake and the lake fauna suffers due to
the high levels of respiration by the living vegetative matter. Eutrophication might occur
naturally or due to human impact on the environment.

Fish culture in Lakes

Hypereutrophic lake

These lakes suffer from problems arising due to excessive plant and algal growth due to
a high supply of growth nutrients. These lakes have little transparency due to the dense
overgrowth of algae or aquatic flora. These lakes have visibility limited to lower than 3 feet.
Hypereutrophic lakes also have more than 100 micrograms/liter of phosphorus and more than
40 micrograms/liter of total chlorophyll. The overgrowth of algae often suffocates the fauna
below the water depths, and this might create dead zones beneath the water surface.