Brackish water
fisheries
The region where the rivers meet the seas is
called estuary. The salinity of these waters is highly variable from 5ppt to
30ppt depending on season and tides of the sea.
The organisms which can tolerate rapid salinity fluctuations only can
survive in these waters. Such organisms
are called euryhaline organisms. The
brackish water is rich in nutrients.
The important estuaries in India include the
Hoooghly estuary where Ganga join bay of Bengal, Mahanadi estuary in Gujarath,
Krishna-Godavari estuary in Andhra Pradesh, Cauvery Estuary in Tamilnadu. Important brackish water lakes are Chilka
lake in orissa, pulicat lake in Tamilnadu, kolleru lake in andhra pradesh.
Types of
Estuaries: The estuaries can be categorised as Open
estuary and Enbanked estuary. In open
estuaries the river directly is connected to the sea. In enbanked estuary the estuary is surrounded
by land. It is connected to the sea
during hightides and heavy rains only. Eg. Lagoons.
Characters of
Estuary
a.
The water is mixure of freshwater and marine
water
b. The pH value of water is between 7.5-8.5
c.
The water is rich in nutrents
d. The Oxygen content will be less
e. It forms a good breeding ground for many fishes
f.
Estuary harbours many Anadromous and
catadromous fishes.
There are about 1.2 million hectares
brackishwater area available in India suitable for farming. Out of it only 13%
only is being utilised.
Important
fishes found in estuaries
a. Mullets form 1/3 of
the total catch of brackish waters. These include species like Mugil
cephalus, M. tade, M. cunnesius,
Valamugil seheli, Liza macrolepis, L. tade, L. parsia. etc. They are caught
almost throughout the year. Mullets are Hallmark of Krishna estuary.
b. Perches: Lates
calcarifer (pearl spot) is the most popular estuarine perch. Others include Holocantrus serranus,
Lethirinus nebulosus, Ambassis ambassis, Terapon jarbua Etc.
c. Cat fishes: These are very
important fishes. These are also
cultured in brackish waters due to their market demand. Important species include – Mystus gulio,
Heteropneustes fossilis, Pangasius sutchi, P. pangasius Arieus, Myceous sp.
etc.
d. Clupeoids: the famous
among this category is Hilsa ilaisha which has commercially high demand. Hilsa
forms major catch of Hoogly estuary. It
is an anadromous fish. Neotilosa, Manon,
Elops sp. are other estuarine clupeoids fishes having economical value.
Other fishes include Chanos chanos (milk fish), Etroplus
suratensis, ribbon fishes etc.
Estuarine Shell
fishery: Shell fishery of estuaries comprise mainly
prawns and crabs. Fish catches from
estuaries are often dominated by prawns and crabs. Pinaeus indicus, P. monodon (Tiger prawn), P. semiselcatus,
Metapenaeus dobsonii, M. monoceros, M. brevicornis are some of the prawns.
Crabs like Scyla serrata, Portunus
pelagicus are found in estuarine waters.
Brackish water
lakes: some lakes are formed by brackish waters. India’s largest such lake is chilka lake in
orissa. It has a length of 70km and
width of 32km. 152 species of different
fishes and 21 species of prawns inhabit this lake.
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