Characteristics of Riverine system Rivers are linear systems, which show a gradient of characters along their length. The longitudinal profile of a river is concave with a steep upper portion near the source, giving way to reaches of progressively less gradient as the mouth is approached. The steep and torrential upper course is called “rhithron” and The flat, slow-flowing lower course is called “potamon” Rhithron zone Rhithron zone characteristics They tend to show an alternation between Steep, narrow and shallow riffles or rapids, Flatter, wider and deeper reaches, termed pools. Turbulent flow and relatively low temperatures characterize this zone. Normally, the water is highly oxygenated, but at low water, the pool and riffle system may break up into a series of pools, whose waters may become completely depleted of oxygen. Adaptations of fishes of rhithron zones Fish species in rhithron zones are entirely rheophilic and are categorized into two groups. The species which lives on or among the rocks and vegetation of the bottom, are distributed predominantly in the riffles. Typically, these are small size and are adapted to grip or cling to the substrate. For such adaptation including the mouth suckers for instance Chiloglanis, ventral friction pads as in Astroblephus or pectoral fin spines adapted as hooks as in Glyptothorax. The species such Barbus or salmo are adapted to swim sufficiently fast as resist to the current and even against it. This they cannot do on a sustained basis, however, and frequently take advantage of cover provided by the slack water of the pools and by snags, overhangs, and other features, which disrupt the current. Because of the severity of the habitat, diversity of resident species tends to be low. Potamon zone Potamon zone Characteristics Potamon reaches with wide, flat, meandering channels, mud bottoms and much rooted and floating vegetation. Zonation within the potamon is both longitudinal and lateral. Longitudinally, there is a repetition of differing habitats associated with the meanders of the channel. Laterally, there is the distinction between the main channel and its floodplain. The floodplain is usually an area of relatively flat land flanking the main channel. In exceptional cases, larger floodplain areas arise by geographic accident. The plain is usually higher near the river, where raised levees limit the main channel, and slopes downward toward the foot of the terrace confining the plain. Many bodies of water are found on the plain ranging from small temporary pools to large permanent lagoons and swamps. The potamon is environmentally more complex than the rhithron. There is usually a well-defined series of river channels flanked by a floodplain. Both the running and still waters may be present. The plain itself contains many types of the water body, some of which retain water throughout the inter-flood period. Because of deposition of silt, such features show a succession from the open lagoon, through vegetation-lined pools and densely vegetated swamps to dry land. In the water bodies of the floodplain, dissolved oxygen concentrations fall in the dry season, particularly in the smaller pools, which may become completely depleted of oxygen. Adaptations of fishes of potamon zones There are two main adaptations, which enable fish to survive the conditions during low waters. The Species, which is specially adapted to resisting the low dissolved oxygen concentration. The adaptations may be in the form of auxiliary respiratory organs for using atmospheric oxygen i.e. Clarias or Notopterus, or may be physiological as with Carassius or even behavioural as with many cyprinodonts. The same species have a capacity to tolerate high temperatures. They have complex breeding habits with multiple spawning, a great degree of parental care, and migrate laterally between the dry season habitat in the river channel and the flood season habitat in the inundated area. Species, which uses the rich habitat provided by the flood plain during the flood but escapes the severe dry season conditions by lateral movement off the plain and longitudinal migration within the main river channel to an alternative habitat. This is usually located in the deeper regions of the main river channel, but may also be in the sea or some other large water body adjacent to the river system. A certain proportion of these species moves upriver, even as far as the rhithron zone. Such fishes show few adaptations other than a capacity for fast and sustained swimming. Their breeding strategy is simple, relying on a single release of a vast number of eggs, either on the flood plain or in the headwater streams. To accomplish this, they may undertake migrations for very long distances up-and down-river. Riverine system classification In India, rivers play a major role in the livelihood of the peoples. The riverine system is categorized into four groups namely Major Rivers Medium Rivers Minor Rivers and Desert Rivers. Most of the rivers pour their water in the Bay of Bengal and some of them though pour in the western parts of India Arabian Sea. Major rivers Major rivers are those which has a catchment area of 20000 km2. There are 14 such major rivers in India. Further, they are classified into Himalayan Rivers and Peninsular rivers based on the origin of the river. S.No. River Total length (km) Distribution over states Length (km) 1 Ganga 2525 (a) Uttar Pradesh 1450 (b) Bihar 445 (c) West Bengal 520 (d) Boundary of Bihar and U.P 110 2 Brahmaputra 916 (a) Arunachal Pradesh 218 (b) Assam 698 3 Indus 1114 Jammu & Kashmir 1114 4 Brahmani 799 (a) Odisha 541 (b) Bihar 258 5 Krishna 1401 (a) Maharashtra 640 (b) Andhra Pradesh 386 (c) Karnataka 375 6 Mahanadi 851 (a) Madhya Pradesh 357 (b) Odisha 494 7 Sabarmathi 371 (a) Rajasthan 48 (b) Gujarat 323 8 Narmadha 1312 (a) Madhya Pradesh 1079 (b) Gujarat 159 (c) Boundary of M.P and Gujarat 39 (d) Boundary of M.P and Maharashtra 35 9 Mahi 583 (a) Madhya Pradesh 167 (b) Rajasthan 174 (c) Gujarat 242 10 Tapti 724 (a) Madhya Pradesh 228 (b) Maharashtra 228 (c) Gujarat 214 (d ) Boundary of M.P and Maharashtra 54 11 Godavari 1465 (a ) Andhra Pradesh 771 (b ) Maharashtra 694 12 Pennar 597 (a) Karnataka 61 (b) Andhra Pradesh 536 13 Cauveri 800 (a ) Karnataka 320 (b) Tamilnadu 416 (c) Boundary of Karnataka and Tamilnadu 64 14 Subarnarekha 395 (a) Jharkhand 269 (b) West Bengal 64 (c ) Orissa 62 Medium rivers A river with a catchment area of 2000 - 20000 km2 is categorized as Medium River. There are 44 such rivers in India, with a total drainage area of 0.24 million square kilometers. Of these rivers, nine rivers are interstate rivers as they flow through more than one state. 17 rivers flow towards the Arabian Sea, 23 flow towards the Bay of Bengal and Four rivers in North Eastern states. Medium river basins S.No Name of the River Village/Dist. (Origin) State Length Catchment (Km.) Area (Sq.Km) 1 Ozat Kathiawar Gujarat 128 3189 2 Shetrunji Dalkania Gujarat 182 5514 3 Bhadar Rajkot Gujarat 198 7094 4 Aji Rajkot Gujarat 106 2139 5 Dhadhar Panchmahal Gujarat 135 2770 6 Purna Dhosa Maharashtra 142 2431 7 Ambika Dangs Maharashtra 171 3637 8 Vaitarna Nasik Maharashtra 143 2357 10 Ulhas Raigarh Maharashtra 64 2174 11 Savitri Pune Maharashtra 99 2899 12 Sastri Ratnagiri Maharashtra 64 2174 13 Washishthi Ratnagiri Maharashtra 48 2239 14 Mandvi Belgaum Karnataka 87 2032 15 Kalinadi Belgaum Karnataka 153 5179 16 Gangavati or Bedti (in upper reaches) Dharwar Karnataka 152 3902 17 Sharavati Shimoga Karnataka 122 2209 18 Netravati Dakshina Kannada Karnataka 103 3657 19 Chaliar or Baypore Elamtalvi Hills Kerala 169 2788 20 Bharathapuzha (known as Ponnani) Annamalai Hills Tamil Nadu 209 6186 21 Periyar Sivajini Hills Kerala 244 5398 22 Pamba Devarmalai Kerala 176 2235 23 Burhabalang Mayurbahanj Odisha 164 4837 24 Baitarni Keonjhar Odisha 365 12789 25 Rushikulya Phullbani Odisha 146 7753 26 Bahuda Ramgirivillage Odisha 73 1248 27 Vamsadhara Kalahandi Odisha 221 10830 28 Nagavali Kalahandi Odisha 217 9410 29 Sarda Vishakhapatnam Andhra Pradesh 104 2725 30 Eleru Vishakhapatnam Andhra Pradesh 125 3809 31 Vogarivagu Guntur Andhra Pradesh 102 1348 32 Gundlakamma Kurnool Andhra Pradesh 220 8494 33 Musi Nellore Andhra Pradesh 112 2219 34 Paleru Nellore Andhra Pradesh 104 2483 35 Muneru Nellore Andhra Pradesh 122 3734 36 Swarnamukhi Koraput Odisha 130 3225 37 Kandleru Vinukonda Andhra Pradesh 73 3534 38 Kortalaiyar Chengalpet Tamilnadu 131 3521 39 Palar (including tributary Cheyyar) Kolar Karnataka 348 17871 40 Varahandi North Arcot Tamilnadu 94 3044 41 Ponnaiyar Kolar Karnataka 396 14130 42 Vellar Chithri Hills Tamilnadu 193 8558 43 Vaigai Madurai Tamilnadu 258 7031 44 Pambar Madurai Tamilnadu 125 3104 45 Gundar Madurai Tamilnadu 146 5647 46 Vaippar Tirunelvelli TamilNadu 130 5288 47 Tambraparni Tirunelvelli TamilNadu 130 5969 48 Subarnarekha Nagri/Ranchi Bihar 395 19296 Total 248505 Minor rivers Minor rivers are those which has the catchment area of less than 2,000 km2. There are numerous and mostly small streams flowing from Western and Eastern Ghats to the sea. The total drainage area is about 0.2km2. Desert Rivers These rivers flow for some distance and disappear in the deserts of Rajasthan. These rivers include Luni, Machai, Rupen, Saraswati, Baner and Ghaggar. The Amblypharyngodon mola, Bari bendelansis, Botia geto, Catla catla, Cirrhina mrigala, C. reba, Labeo spp, Danio devario, D. rerio, Tor tor, Nemacheilus botia, Puntius spp, Rasbora daniconius, Mastacembelus armatus, Channa spp., Trichogaster fasciatus, Clarias batrachus, Mystus spp, Heteropneustes fossilis, Wallago attu, Notopterus spp.,are the major fishes.