ESTUARINE FISH FARMING
141
and tidal flats, that the major control of the ecosystem should be that
of the activity of processes on and in the bottom sediments.”
I n a walled-off Hawaiian tidal fishpond, Malone (1969) found that
gross primary productivity equalled 445 g C/m2/year, and of this 347
were contributed by the benthos, and only 98 by plankton. Pillay
(1954) writes of the bheris of West Bengal, that the picture of biotic
interaction in the ponds indicates a high demand on the benthic
vegetation and a negligible one on surface plankton.
It is common experience in fish culture that plankton and benthos
are to a large extent antagonistic. If plankton develops and produces
turbidity, the benthos is shaded out, while if the benthos is well established and flourishing, it leaves little nutrient material for the plankton.
Plainly, shallow water will favour the benthos, and since the fish
cultivated in brackish-water fishponds on estuaries are feeders on the
benthos, the water of these ponds is shallow. When fertilizers are used,
they are of the slow-acting kind which acts on the benthos : the more
familiar soluble inorganic fertilizers now so successfully used in freshwater fishponds are ineffective in these shallow estuarine ponds.
Estuarine fish farming is based on the exploitation of the great
natural fertility of this environment by some control of the rate of
stocking with fish, and some control of predators and competitors
which would reduce the useful crop of fish. I n many cases, so little is
done in the way of management that purists might object to the use
of the expression “ fish farming ”.
3. Detritus
The fertility of estuaries is also associated with the presence of
abundant detritus, and the detritus cycle plays a vital part. The
estuarine ecosystem is “ a mixing region between sea and inland water
of such shape and depth that the net resident time of suspended
materials exceeds the flushing ” (Hedgpeth, 1967-8) “ Thus the system
constitutes a nutrient trap ’,. d’Ancona (1954) ascribes the high rate
of production in the brackish-waters of the north Italian lagoons to
the mineralization of organic substances carried into the lagoon with
the tidal current, which brings in more plankton than is removed by
the outflow. Again, this is an accumulation of organic material.
Detritus has been defined by Darnell (1967) as “ all types of organic
material in various stages of microbial decomposition which represent
potential energy sources for consumer organisms ”. For convenience,
he recognizes two states of detritus, the particulate and the nonparticulate ; many forms of microbiota are associated with a decomposing substrate.
141
and tidal flats, that the major control of the ecosystem should be that
of the activity of processes on and in the bottom sediments.”
I n a walled-off Hawaiian tidal fishpond, Malone (1969) found that
gross primary productivity equalled 445 g C/m2/year, and of this 347
were contributed by the benthos, and only 98 by plankton. Pillay
(1954) writes of the bheris of West Bengal, that the picture of biotic
interaction in the ponds indicates a high demand on the benthic
vegetation and a negligible one on surface plankton.
It is common experience in fish culture that plankton and benthos
are to a large extent antagonistic. If plankton develops and produces
turbidity, the benthos is shaded out, while if the benthos is well established and flourishing, it leaves little nutrient material for the plankton.
Plainly, shallow water will favour the benthos, and since the fish
cultivated in brackish-water fishponds on estuaries are feeders on the
benthos, the water of these ponds is shallow. When fertilizers are used,
they are of the slow-acting kind which acts on the benthos : the more
familiar soluble inorganic fertilizers now so successfully used in freshwater fishponds are ineffective in these shallow estuarine ponds.
Estuarine fish farming is based on the exploitation of the great
natural fertility of this environment by some control of the rate of
stocking with fish, and some control of predators and competitors
which would reduce the useful crop of fish. I n many cases, so little is
done in the way of management that purists might object to the use
of the expression “ fish farming ”.
3. Detritus
The fertility of estuaries is also associated with the presence of
abundant detritus, and the detritus cycle plays a vital part. The
estuarine ecosystem is “ a mixing region between sea and inland water
of such shape and depth that the net resident time of suspended
materials exceeds the flushing ” (Hedgpeth, 1967-8) “ Thus the system
constitutes a nutrient trap ’,. d’Ancona (1954) ascribes the high rate
of production in the brackish-waters of the north Italian lagoons to
the mineralization of organic substances carried into the lagoon with
the tidal current, which brings in more plankton than is removed by
the outflow. Again, this is an accumulation of organic material.
Detritus has been defined by Darnell (1967) as “ all types of organic
material in various stages of microbial decomposition which represent
potential energy sources for consumer organisms ”. For convenience,
he recognizes two states of detritus, the particulate and the nonparticulate ; many forms of microbiota are associated with a decomposing substrate.