INTRODUCTION:

Fish constitutes almost half the total number of vertebrates. Of the 39,000 species of vertebrates recognised the world over, 21,723 are fish species of which 8,411 species are freshwater, while 11,650 are marine. India has 2500 freshwater and 1570 marine species. In terms of habitat diversity, fishes live in almost every conceivable aquatic habitat. Approximately, 71% of the earth's surface is water to an average depth of 3800m. The inland water covers less than 5.5% of the earth's surface of 2500000 km2. India has a total lotic length of 1,12,650 km; while, the total lake coverage is 720000 ha. In Assam, on the other hand, the total riverine length is 4,500 km; while the total area covered by 'Beel' is 1 lac hectare. In Assam, the Beels alone constitute 81% of the total lentic area of 120000 ha.

In Barak valley region of Assam, Barak is the principal river, which originates from Javpo peak (11,000 ft high) in Nagaland. Barak has a number of tributaries joining it, notably Jiri, Chiri, Madhura and Jatinga on the north bank; while Sonai, Rukni, Gaghra, Dhaleswari and Tuivai join the river on the south bank. Before entering Bangladesh, Barak bifurcates into two branches, viz, the river Surma, which enters Bangladesh and the river Kushyara, which after flowing for some distance along the Indo-Bangladesh border enters Bangladesh.

The river Surma joins the river Baleswar, while the river Kushyara joins the rivers Singla and Longai. The province of Mizoram is situated on the southern part of Northeast India bordering Bangladesh on the west and Myanmar on the east having the Tropic of Cancer passing through it. The major rivers of Mizoram are the Tuirial, Tuirini (Seruli), Tlawang and Tuivai, which join the Barak drainage at different locations on its course. As recorded till date, among these rivers, Tuirial revealed the occurrence of 14 species, Tlawang contained 6 species at Sairong landing centre and 3 less abundant species at Bairabi landing centre. The river Tuivai contained four less abundant species; while the river Tuirini in the little downstream zone (called the river Seruli) has been found to contain 10 distinct species.

The river Chhimtuipui originates in Myanmar flows northwards along the Indo-Myanmar border and flows back into Myanmar again. The river Mat joins the river Chhimtuipui in Mizoram. The province of Tripura is a region flanked by hills and plains having five principal rivers flowing through its terrain, viz, the river Manu, Khowai, Howrah, Gomati and Feni. Of these, the river Manu and Gomati originate from Longtarai hills while the river Khowai originates from the Atharamura hill ranges. The river Howrah originates from Baramura hills. Many studies have been done on the ichthyodiversity of rivers in India and abroad; notably, Chaudhuri (1916), Menon (1951, 1974, 1999), Jayaram (1981,1999), Sen (1982), Kar (1984), Kar & Dey (1992 &2000), Kar &Barbhuiya (2000), Jordan (1923), Berg (1940), Banarescu and Nalbant (1964), Greenwood et al (1966) and Banarescu and Herzig-Straschil (1995).

MATERIALS AND METHODS:

Fish samples were collected using 3.5m dia cast net and 100 x 1.5m dimension gill nets. Fish samples were also collected through random sampling from the fish landing centres (FAO, 1974). The specimens were immersed immediately in concentrated formalin for proper orientation and then preserved finally in 10% formalin. Fishes were identified after standard literature survey (Hamilton, 1822; Day, 1878 & 1889; Shaw and Shebbeare, 1938; Mishra, 1959; Menon, 1974 & 1999; Jayaram, 1981 & 1999; Greenwood et al, 1966).

OBSERVATIONS AND DISCUSSION:

The lists of ichthyofauna of the river Barak and its principal tributaries, have been presented in Tables 1-10; while the lists of fish fauna of the major rivers of Mizoram, have been presented in Tables 11-17. The fish fauna of the major rivers of Tripura are listed in Tables 18-21. Zoogeographically, different workers had classified freshwater fish variously. The freshwater fish of marine origin has been further classified as peripheral freshwater forms. The ichthyospecies of this region have been found to belong to two broad categories, viz, widely distributed species and species of Northern India. Ecomorphologically (Dey, 1973), the ichthyofauna of this region could further be included into four distinct groups, viz. True hill stream group, semi torrential forms, migratory varieties and plain water types.

The truly freshwater fishes have unique significance in zoogeographical interpretations because they are as closely bound to land masses as are any terrestrial animals and are almost confined to their own drainage Systems. Generally, they can pass from one isolated drainage system to another only through the slow physiographic change of the land. They possess a physiological inability to survive in the seawater and hence their dispersal over the globe is slow. As such, they are most likely to preserve old distribution patterns (Darlington, 1957). The range of distribution of torrential fishes is much more limited and in view of their limited power of migration, torrential fishes afford better evidence of zoogeographical relationships (Hora, 1944). As such, many fish groups are important in explaining their regional and local distribution patterns.

TABLE 1: LIST OF FISHES OF RIVER BARAK

TABLE 2: LIST OF FISHES OF RIVER SONAI

TABLE 3: LIST OF FISHES OF RIVER RUKNI

TABLE 4: LIST OF FISHES OF RIVER JIRI

TABLE 5: LIST OF FISHES OF RIVER CHIRI

1	Amblypharyngodon mola
2	Neolissochilus hexagonolepis
3	Heteropneustes fossilis
4	Channa punctatus

TABLE 6: LIST OF FISHES OF RIVER MADHURA

TABLE 7: LIST OF FISHES OF RIVER JATINGA

TABLE 8: LIST OF FISHES OF RIVER GHAGRA

1	Rasbora daniconius
2	Osteobroma cotio
3	Mystus occulatus
4	Mystus vittatus
5	Gagata gagata
6	Chanda nama

TABLE 9: LIST OF FISHES OF RIVER KATAKAHAL (DHALESWARI)

TABLE 10 : LIST OF FISHES OF RIVER BALESWAR

TABLE 11: LIST OF FISHES OF RIVER TUIRIAL IN MIZORAM

TABLE 12: LIST OF FISHES OF RIVER TUIRINI (SERULI) IN MIZORAM

1	Securicula gora
2	Aspidoparia morar
3	Barilius shacra
4	Chela laubuca
5	Neolissochilus hexagonolepis
6	Puntius chola
7	Mystus vittatus
8	Chanda nama
9	Glossogobius giuris

TABLE 13 : LIST OF FISHES OF RIVER TLAWANG IN MIZORAM

1	Securicula gora
2	Barilius tileo
3	Barilius vagra vagra
4	Cirrhinus reba
5	Cirrhinus mrigala
6	Labeo calbasu
7	Labeo rohita
8	Clupisoma garua
9	Glossogobius girusis

TABLE 14: LIST OF FISHES OF RIVER TUIVAI IN MIZORAM

1	Barilius shacra
2	Tor mosal
3	Chagunius chagunio
4	Puntius clavatus

TABLE 15: LIST OF FISHES OF RIVER MAT IN MIZORAM

TABLE 16: LIST OF FISHES OF RIVER CHHIMTUIPUI (KOLODYNE/KALADAN) IN MIZORAM

TABLE 17: LIST OF FISHES OF RIVER KARNAFULI (TLABUNG) IN MIZORAM

TABLE 18: LIST OF FISHES OF RIVER MANU IN TRIPURA

TABLE 19: LIST OF THE FISHES OF RIVER KHOWAI IN TRIPURA

1	Notopterus notopterus
2	Amblypharyngodon mola
3	Cirrhinus mrigala
4	Glossogobius giruris
5	Channa punctatus

TABLE 20: LIST OF FISHES OF RIVER HOWRAH IN TRIPURA

TABLE 21: LIST OF FISHES OF THE RIVER GOMATI IN TRIPURA

Address:

1. Department of Zoology,
Gauhati University,
Guwahati-14,
India.

2. Department of Life Science,
Assam (Central) University,
Silchar-788011,
India