Inland Fisheries

Classification of Lakes

Welch (1952) classified lakes into three types based on the nutrient status of the lake. They are namely,

1. Oligotrophic lakes

These lakes are very deep. Littoral and sub-littoral zones are narrow and less productive. Profundal zone is extensive. They are poor in nutrients. Oxygen is at high concentration in hypoliminion. Phytoplankton are low in density. These types of lakes are found in India.

2. Eutrophic lakes

These lakes are very shallow and warmer. Littoral and sub-littoral zones are abundant, sides are sloppy and bottom is sandy. They are rich in nutrients. Primary production is high due to light penetration and availability of oxygen. Phytoplankton are high in density. These types of lakes are also found in India.

3. Dystrophic lakes

These lakes have high concentration of humic acid making water unsuitable for organisms to grow. Oxygen is nearly lacking. They are rich in phosphorus, nitrogen and organic materials. However, calcium is absent. These types of lakes are also available in India.

Broadly, the lakes in the uplands of India are of two types. They are

1. Lakes which do not feeze at any time of the year

This type of lakes is generally situated in valleys or plateaus at relatively higher elevations. These are Wular in Kashmir, the Renuka in Himachal Pradesh, the Bhimtal, and the Devariatal in Uttar Pradesh, the Nainital and the Sattal in Uttaranchal, the Ooty and the Kodaikanal in Tamil Nadu and the Devikulam and the Elephant in Kerala.

2. Lakes which feeze partly or fully during a part of the year

This type of lakes is generally situated in higher elevations. These are the Dal, Kishansar, Vishensar, Shishnag, Tarsar, Marsar and the Neelnaa which remain frozen for a considerable part of the year. Most of these lakes except the Dal and the Wular in Kashmir are small ranging between 1.8 and 9.3 ha in area. Although the majority of the upland lakes are fresh water, yet there are several salt water lakes in Ladakh, notably the Pangar, Tso and the Ts, Moriri.

These lakes support a lucrative indigenous and exotic fish fauna comprising snow trouts, trouts, mahseers, crucian carps, mirror carps and tenches.