235
Hora’s hypothesis after a detailed analysis of 89
genera of Indian FW fi shes and had stated that
the fi sh fauna of India was related to the Malayan
region, and that it hardly had contained any typical Ethiopian element. A close kinship with forms
in countries towards the east of India, namely,
Myanmar (earlier Burma), Malaya, Sumatra, Java,
could be revealed through a careful examination
of the Indian endemic genera (Jhingran 1991 ).
Incidentally, Menon ( 1955 ) had recorded the following fi sh genera as endemic and exclusive to
India: Parapsilorhynchus Hora, Lepidopygopsis
Raj, Balitora Gray, Bhavania Gray, Somileptus
Swainson, Horabagrus Jayaram, Hara Blyth,
Sisor Hamilton-Buchanan, Ctenops McClelland,
Ailia Gray, Silonia Swainson, etc.
It is sometimes believed that the Assam land
route between peninsular India and the north
became submerged during the Middle Eocene
owing to the transgression of the Bay of Bengal
(Menon and Prashad 1961 ). From Eocene
onwards extending up to the early Pliocene, the
Bay of Bengal had extended northwards to China
and Tibet. This had, perhaps, separated India
from the rest of Asia; and, therefore, the monsoonbearing winds crossed to the north over this gulf,
thus making the Yunnan region, which, at that
time, was, perhaps, a low land situated nearer to
the equator having temperate climate (Hora
1953 ). These conditions, possibly, favoured the
evolution of a diverse and specialised fi sh fauna
in the Yunnan region. The same, however, did not
spread to India until the Pliocene, when, with the
major upheaval of the Himalayas, the arm of the
sea became shallow and transformed into brackish water lakes and lagoons. The land link
between India and the Far East was, thus, once
again formed. West tropical marshy conditions
corresponding to those of the Siwaliks seem to
have prevailed along the entire length of the
southern face of the Himalayas extending eastwards to areas beyond China and westwards to
Baluchistan during the Pliocene synchronising
with the upheaval of the Himalayas. During this
period, there had been a dispersal of fi shes inhabiting the marshes, as is evidenced from the fossil
relics of forms like Clarias, Heteropneustes,
Channa, Rita, Bagarius and Silurus . Fishes,
which are typical of the smaller torrential streams,
also followed a more or less parallel history of
emergence in the early Pleistocene. The typical
Himalayan ichthyofauna, like Nemacheilus,
Garra and Tor , perhaps, had originated somewhere in the south of China and dispersed into
the regions lying along the Alpine–Himalayan
system and its southern loops ramifying into
Europe, Western Asia and other associated mountains (Hora 1951a ). A second major upheaval of
the Himalayas had occurred towards the end of
the Pliocene or early Pleistocene which had, perhaps, raised the Siwalik sediments into dry land.
Concomitantly, it is assumed that the Siwalik
fore-deep had gradually disappeared, leaving a
shallow depression, referred to as the ‘Pleistocene
fore-deep’, which, meanwhile, along with the
formation of ‘Assam Plateau’, began draining the
northern part of India, beginning from Assam,
into the Arabian Sea (Hora 1953 ). It is, further,
believed that at certain point of time, there might
have existed a contiguous route which had linked
the Asian Plateau in the east with the headwaters
of the Euphrates and the Tigris Rivers along
which the fi shes might have got widely dispersed
(Menon 1955 ).
Most of the present-day fi sh fauna of India,
however, had descended from the Pleistocene
migrants. Migration along the Himalayas westwards might have commenced during the early
Pleistocene and might have continued uninterrupted till the late Pleistocene, when the dismemberment of the westward-fl owing drainage at the
foot of the Himalayas had occurred. However,
migration southwards to the peninsula might
have occurred entirely during the Pleistocene. It
is assumed that from the beginning of the
Pleistocene, the sea level had undergone repeated
fl uctuations which were supposed to have been
caused by the formation of large ice caps on the
higher latitudes during the glacial period and
their subsequent melting during the inter-glacial
periods. The former, obviously, might have lowered the sea level and the latter had led to its rise.
However, during the last glacial period, the sea
level had increased, probably, due to changes in
climate. Hora ( 1951b ) had advocated that during
the glacial periods (pluvial periods in the southern
15.5 Wetland Fishes
Hora’s hypothesis after a detailed analysis of 89
genera of Indian FW fi shes and had stated that
the fi sh fauna of India was related to the Malayan
region, and that it hardly had contained any typical Ethiopian element. A close kinship with forms
in countries towards the east of India, namely,
Myanmar (earlier Burma), Malaya, Sumatra, Java,
could be revealed through a careful examination
of the Indian endemic genera (Jhingran 1991 ).
Incidentally, Menon ( 1955 ) had recorded the following fi sh genera as endemic and exclusive to
India: Parapsilorhynchus Hora, Lepidopygopsis
Raj, Balitora Gray, Bhavania Gray, Somileptus
Swainson, Horabagrus Jayaram, Hara Blyth,
Sisor Hamilton-Buchanan, Ctenops McClelland,
Ailia Gray, Silonia Swainson, etc.
It is sometimes believed that the Assam land
route between peninsular India and the north
became submerged during the Middle Eocene
owing to the transgression of the Bay of Bengal
(Menon and Prashad 1961 ). From Eocene
onwards extending up to the early Pliocene, the
Bay of Bengal had extended northwards to China
and Tibet. This had, perhaps, separated India
from the rest of Asia; and, therefore, the monsoonbearing winds crossed to the north over this gulf,
thus making the Yunnan region, which, at that
time, was, perhaps, a low land situated nearer to
the equator having temperate climate (Hora
1953 ). These conditions, possibly, favoured the
evolution of a diverse and specialised fi sh fauna
in the Yunnan region. The same, however, did not
spread to India until the Pliocene, when, with the
major upheaval of the Himalayas, the arm of the
sea became shallow and transformed into brackish water lakes and lagoons. The land link
between India and the Far East was, thus, once
again formed. West tropical marshy conditions
corresponding to those of the Siwaliks seem to
have prevailed along the entire length of the
southern face of the Himalayas extending eastwards to areas beyond China and westwards to
Baluchistan during the Pliocene synchronising
with the upheaval of the Himalayas. During this
period, there had been a dispersal of fi shes inhabiting the marshes, as is evidenced from the fossil
relics of forms like Clarias, Heteropneustes,
Channa, Rita, Bagarius and Silurus . Fishes,
which are typical of the smaller torrential streams,
also followed a more or less parallel history of
emergence in the early Pleistocene. The typical
Himalayan ichthyofauna, like Nemacheilus,
Garra and Tor , perhaps, had originated somewhere in the south of China and dispersed into
the regions lying along the Alpine–Himalayan
system and its southern loops ramifying into
Europe, Western Asia and other associated mountains (Hora 1951a ). A second major upheaval of
the Himalayas had occurred towards the end of
the Pliocene or early Pleistocene which had, perhaps, raised the Siwalik sediments into dry land.
Concomitantly, it is assumed that the Siwalik
fore-deep had gradually disappeared, leaving a
shallow depression, referred to as the ‘Pleistocene
fore-deep’, which, meanwhile, along with the
formation of ‘Assam Plateau’, began draining the
northern part of India, beginning from Assam,
into the Arabian Sea (Hora 1953 ). It is, further,
believed that at certain point of time, there might
have existed a contiguous route which had linked
the Asian Plateau in the east with the headwaters
of the Euphrates and the Tigris Rivers along
which the fi shes might have got widely dispersed
(Menon 1955 ).
Most of the present-day fi sh fauna of India,
however, had descended from the Pleistocene
migrants. Migration along the Himalayas westwards might have commenced during the early
Pleistocene and might have continued uninterrupted till the late Pleistocene, when the dismemberment of the westward-fl owing drainage at the
foot of the Himalayas had occurred. However,
migration southwards to the peninsula might
have occurred entirely during the Pleistocene. It
is assumed that from the beginning of the
Pleistocene, the sea level had undergone repeated
fl uctuations which were supposed to have been
caused by the formation of large ice caps on the
higher latitudes during the glacial period and
their subsequent melting during the inter-glacial
periods. The former, obviously, might have lowered the sea level and the latter had led to its rise.
However, during the last glacial period, the sea
level had increased, probably, due to changes in
climate. Hora ( 1951b ) had advocated that during
the glacial periods (pluvial periods in the southern
15.5 Wetland Fishes