Freshwater Molluscs of India: An Insight of into Their Diversity, Distribution and Conservation - Aquatic Ecosystem: Biodiversity, Ecology and Conservation - page 160

Freshwater Molluscs Used as Food

but bivalves live partly buried in the sand or mud.
Similar to the gastropods, the bivalves exhibit
variations in shell depending upon the ecology of
the species and may produce ecophenotypes
(Subba Rao 1989 ).

The freshwater molluscs are important as additional
resources of protein for the increasing human
population of our country. An increase in the
shell production can augment our protein-rich
food supply. It has been observed that at least 22
freshwater species are used as food and there is
regular sell of shellfi sh in several markets of
eastern (West Bengal) and northeastern states
(Table 11.1 ). Shellfi shes are harvested from the
natural resources by different methods and
brought to the markets. There are no regular markets
in some places, but still people use the shellfi sh
as food very frequently. It is very popular among
poor and tribal people of India.

Anhydrobiosis

Freshwater molluscs are usually faced with an
annual dry season. Gastropods and bivalves
show varying capacity to survive desiccation.
Many snails can overcome this by aestivation
either under dead vegetation, rocks, bricks or
debris or actively burrowing at least the aperture
of the shell in the mud. Some shells are capable
of anaerobic respiration. With the advent of
favourable conditions, the molluscs resume to
their normal activities. The discontinuous and
transient nature of freshwater bodies leads
to isolation of snails or bivalves into small local
populations. Nevertheless, much remains to be
worked on the ecology of Indian freshwater
molluscs.

Freshwater Molluscs and Diseases

In India, millions of people and their livestock are
infected with schistosomiasis, amphistomiasis,
and paragonimiasis and other trematode para-
sites. Efforts to control schistosomiasis and other
snail-borne diseases depend to a great extent on
knowledge of the freshwater snails which serve
as intermediate hosts for the parasites.
Freshwater molluscs are the carrier for schis-
tosomiasis (Bilharziasis) in humans. The only
report of this disease in the assessment region is
in Gimi Village in Ratnagiri District of
Maharashtra State (Gaitonde et al. 1981 ). The
freshwater molluscs species Ferrissia tenuis (LC)
(Bourguignat 1862 ) is a target species for control
programmes against Schistosoma haematobium .
Other species from which schistosome infection
has been reported are in L. exustus and L. luteola
(Table 11.2 ). The question of the transmission of
urinary schistosomiasis elsewhere in India still
remains a mystery. Future research should focus
on this (Table 11.3 ).

Role of Freshwater Molluscs
in the Ecosystem

Freshwater molluscs are one of the most diverse
and threatened groups of animals (Vaughn et al.
2004 ; Lydeard et al. 2004 ). They are mostly unob-
trusive and are not normally considered charis-
matic creatures, rarely attracting the attention of
the popular media, unless in a negative light, as
some species play a signifi cant role (as a vector)
in the transmission of human and livestock para-
sites and diseases (Sinha and Srivastava 1960 ).
This is unfortunate, as they also play a key role in
the provision of ecosystem services and are essen-
tial to the maintenance of wetlands, primarily due
to their contribution to water quality and nutrient
cycling through fi lter-feeding, algal-grazing, and
as a food source to other animals (Strayer et al.
1999 ; Vaughn et al. 2004 , 2008 ; Howard and
Cuffey 2006 ). Some species are of high commer-
cial value as food or ornaments (e.g. clams and
some mussels and snails).

Distribution

In India distribution of the freshwater molluscs
shows some peculiarity that is scattered and
discontinuous distribution of major species.