Inland Fisheries

Riverine Ecosystem

Various reaches of the river systems include Rhithron zone and Potamon zone.

1) Rhithron

Steep and torrential upper course of the river is called the rhithron zone. Low temperature and turbulence are the two main characteristics of the rhithron. Fish fauna of the rhithron zone is entirely rheophilic and falls into two main groups viz.

1. They live beneath the rocks, and on vegetation of the bottom. They are small sized fishes provided with clinging apparatus (such as mouth, suckers, ventral pads or pectoral fins and spines adapted as hooks). Mastacembelus have long sinuous shape; live in the crevices in the rocky bottom.
2. They are well adapted to swim sufficiently fast against the current. eg. Barbus and Salmo sp.

2) Potamon

Flat slow flowing river course is called the potamon zone. This zone combines both lentic and lotic waters and is more complex than rhithron. Fishes living here are adapted to survive in low water level and low oxygen concentration. The adaptation may be in the form of ancillary respiratory organs as in Clarias, Heteropneustes and Channa sp. or may be physiological as with Carassius sp. or even behavioural as with many cyprinodonts. They are characterized with complex breeding habits with multiple spawning and a great degree of parental care. The other category of fishes utilize the rich habitat provided by the flood plains during the floods but escape the severe dry season condition by lateral movement off the plain and longitudinal migration within the main river channel. Certain fishes, viz. Mahseers ascend the river as far as the rhithron zone.

The rivers of India play an important role in the lives of the Indian people. The riverine system of the country comprises four groups of rivers viz. major rivers, medium rivers, minor rivers and desert rivers. Most of the rivers pour their waters into the Bay of Bengal. Some of the rivers whose courses take them through the western part of the country and towards the east of the state of Himachal Pradesh empty into the Arabian Sea. Parts of Ladakh, northern parts of the Aravalli range and the arid parts of the Thar Desert have inland drainage. Different river systems of the country with a combined length of 29,000 km offer one of the richest fish genetic resources of the world. Their highly diverse natural fish fauna characterizes Indian rivers. All these water bodies have about 930 fish species belonging to 326 genera.Though proper riverine production data are not available, the data collected by CIFRI, Barrackpore on selected stretches of the rivers, Ganga, Brahmaputra, Narmada, Tapti, Godavari and Krishna shows that fish production from these rivers vary from 0.64 to 1.64 tonnes per km, with an average of 1 tonne per km. The riverine fisheries resources contribute significantly to the total inland capture fisheries production. The riverine ecosystem witnessed marked alterations due to water abstraction, dam construction, sedimentation and irrational fishing. These activities affected the natural riverine fish production showing continuous declining trend.

Based on the migratory habits, fishes occurring in Indian rivers are classified as:

1. Resident species

The fish species which prefer to remain confined within the local territories are termed resident species. This type includes Cyprinus carpio, Notopterus spp., Channa spp., Mastecembelus spp., Garra, Osteobrama, Puntius, Labeo, Cirrhinus, Mystus, Clupisoma etc.

2. Local migrants

The fish species which perform seasonal migrations within short distances for feeding, breeding etc., are called local migrants. This type comprises of mahseer, Indian major carps, large and medium sized catfishes (like Bagarius bagarius), salmons, trouts etc.

3. Long distant migrants

The fish species which perform regular annual migrations for feeding or spawning or for both are called long distant migrants. This type consists of Indian shad (Hilsa ilisha) - an anadromous fish, freshwater eel (Anguilla spp.) - a catadromous fish and catfish (Pangasius pangasius , migrate from river to estuary).