246
where there is no supplementary feeding. Annual
fi sh yields to the tune of about 3,000 kg/ha/year
could be obtained (Jhingran 1991 ) as compared
to 500–700 kg/ha/year of cattle fl esh.
Pillay ( 1976 ) had predicted that world
aquaculture production could probably double to
12 million metric tonne (mmt) by 1985 as compared to the yield in 1976. It could further increase
fi ve- to tenfold in three decades. Although, the
1985 prediction seems to be possible, the longer
range estimate may be too optimistic. Indeed,
there are possibilities of accomplishing dramatic
future increases in aquaculture yields with the
present- day technology through adopting some of
the following suggestions:
(a) Devoting more area to aquaculture.
(b) Employing polyculture technique in farming.
(c) Increasing feeding and breeding effi ciencies
through genetic selection.
Concomitantly, as given below, a number of factors exist which may limit future production:
(a) Limitation of space for expansion. This is particularly true for the ‘developed’ countries,
where other purposes, such as industry and
recreation, actively compete for the same sites.
(b) Aquaculture industry may be severely
harmed by increased water pollution. Of late,
this has been a serious problem in industrialised nations like Japan.
(c) Future shortages coupled with burgeoning
cost of fertilisers, feeds, petroleum products,
etc., may drive the cost of the fi nal product
too high and may even render aquaculture
practices impractical.
(d) Aquacultural activities may also be prevented or limited by occasional, but indiscriminate, imposition of environmental
protection regulations, many of which may
be designed for other types of industries.
Such a practice is said to be in vogue in the
USA, where aquaculture ponds have been
considered in the same category as the sewage treatment plants. As such, the latter are
also required to regulate their releases of
nutrient and high BOD-laden waters. Such a
measure may sometimes be necessary for
erring industries, but it poses serious hindrances for the aquaculture industries.
Despite the hindrances and diffi culties limiting progress, as outlined above, aquaculture, still,
is showing defi nite signs of growth at a greater
rate than conventional fi sheries. In this context, it
could be said that there are large stretches of habitats, both inland and coastal, particularly in the
tropics. They have low natural productivity and
no other obvious uses. They, thus, could be used
for moderately intensive pond culture of fi shes
like the carps, mullets and milkfi sh. If these are
developed in a rational manner, there may be possibilities of achieving optimistic estimates of
50–60 mmt by the early twenty-fi rst century.
There have been many works on the utilisation
of aquatic resources by man. Two important
works on the general topic of food from the
aquatic bodies are those of Rounsefell ( 1975 ) and
Bell ( 1978 ). Gulland ( 1974 ) and Cushing ( 1977 )
dealt with management of conventional fi sheries.
On the other hand, May et al . ( 1979 ) had presented an innovative modeling approach to the
management of multispecies fi sheries. The
details of the ups and downs of the Peruvian
anchoveta fi shery were reported by Idyll ( 1973 ).
The potential of the Antarctic krill fi shery had
been analysed by El-Sayed and McWhinne
( 1979 ). Bardach et al . ( 1972 ) had created an
extensive database on aquaculture. On the other
hand, Reay ( 1979 ) had published a condensed
literature on aquaculture. However, the question
of ultimate limits on fi shery yields had been
dealt with by Ryther ( 1969 ) and Alversond et al.
( 1970 ). Notwithstanding the above, Whittaker
and Likens ( 1975 ) had developed useful database,
and they also produced a convenient survey of
total biosphere productivity and yields.
Summary
1. The aquatic macrophytes (AM) are interesting forms of plant life. As compared to the
terrestrial plants, the aquatic plants remain
comparatively less affected by the climatic
and seasonal changes. Also, wetland plants
differ from their dry-land cousins in absorbing nitrogen as the NH 4
+ cation because
denitrifying microbes scavenge nitrate.
2. The plant anatomists noted that aquatic plants
are sometimes unusually porous. Their tissues
15 Wetland Flora, Plankton, Productivity, Fauna and Fishes
where there is no supplementary feeding. Annual
fi sh yields to the tune of about 3,000 kg/ha/year
could be obtained (Jhingran 1991 ) as compared
to 500–700 kg/ha/year of cattle fl esh.
Pillay ( 1976 ) had predicted that world
aquaculture production could probably double to
12 million metric tonne (mmt) by 1985 as compared to the yield in 1976. It could further increase
fi ve- to tenfold in three decades. Although, the
1985 prediction seems to be possible, the longer
range estimate may be too optimistic. Indeed,
there are possibilities of accomplishing dramatic
future increases in aquaculture yields with the
present- day technology through adopting some of
the following suggestions:
(a) Devoting more area to aquaculture.
(b) Employing polyculture technique in farming.
(c) Increasing feeding and breeding effi ciencies
through genetic selection.
Concomitantly, as given below, a number of factors exist which may limit future production:
(a) Limitation of space for expansion. This is particularly true for the ‘developed’ countries,
where other purposes, such as industry and
recreation, actively compete for the same sites.
(b) Aquaculture industry may be severely
harmed by increased water pollution. Of late,
this has been a serious problem in industrialised nations like Japan.
(c) Future shortages coupled with burgeoning
cost of fertilisers, feeds, petroleum products,
etc., may drive the cost of the fi nal product
too high and may even render aquaculture
practices impractical.
(d) Aquacultural activities may also be prevented or limited by occasional, but indiscriminate, imposition of environmental
protection regulations, many of which may
be designed for other types of industries.
Such a practice is said to be in vogue in the
USA, where aquaculture ponds have been
considered in the same category as the sewage treatment plants. As such, the latter are
also required to regulate their releases of
nutrient and high BOD-laden waters. Such a
measure may sometimes be necessary for
erring industries, but it poses serious hindrances for the aquaculture industries.
Despite the hindrances and diffi culties limiting progress, as outlined above, aquaculture, still,
is showing defi nite signs of growth at a greater
rate than conventional fi sheries. In this context, it
could be said that there are large stretches of habitats, both inland and coastal, particularly in the
tropics. They have low natural productivity and
no other obvious uses. They, thus, could be used
for moderately intensive pond culture of fi shes
like the carps, mullets and milkfi sh. If these are
developed in a rational manner, there may be possibilities of achieving optimistic estimates of
50–60 mmt by the early twenty-fi rst century.
There have been many works on the utilisation
of aquatic resources by man. Two important
works on the general topic of food from the
aquatic bodies are those of Rounsefell ( 1975 ) and
Bell ( 1978 ). Gulland ( 1974 ) and Cushing ( 1977 )
dealt with management of conventional fi sheries.
On the other hand, May et al . ( 1979 ) had presented an innovative modeling approach to the
management of multispecies fi sheries. The
details of the ups and downs of the Peruvian
anchoveta fi shery were reported by Idyll ( 1973 ).
The potential of the Antarctic krill fi shery had
been analysed by El-Sayed and McWhinne
( 1979 ). Bardach et al . ( 1972 ) had created an
extensive database on aquaculture. On the other
hand, Reay ( 1979 ) had published a condensed
literature on aquaculture. However, the question
of ultimate limits on fi shery yields had been
dealt with by Ryther ( 1969 ) and Alversond et al.
( 1970 ). Notwithstanding the above, Whittaker
and Likens ( 1975 ) had developed useful database,
and they also produced a convenient survey of
total biosphere productivity and yields.
Summary
1. The aquatic macrophytes (AM) are interesting forms of plant life. As compared to the
terrestrial plants, the aquatic plants remain
comparatively less affected by the climatic
and seasonal changes. Also, wetland plants
differ from their dry-land cousins in absorbing nitrogen as the NH 4
+ cation because
denitrifying microbes scavenge nitrate.
2. The plant anatomists noted that aquatic plants
are sometimes unusually porous. Their tissues
15 Wetland Flora, Plankton, Productivity, Fauna and Fishes