122
C. F. HICKLING
though the results are impressive. The barrier of posts, and the traps,
are derived from a very primitive fishing device called a fish fence. A
further evolution is the now-superseded semi-arginate valle of the
north Adriatic, in which the fish were enclosed within palisades to
grow ; and also the great pounds, made largely of netting supported on
concrete piling, in which the Japanese cultivate intensively the yellowtail (Seriola), puffer (Fugu), and prawn. The free access of water allows
a far greater weight of fish than could possibly be supported by the
natural fertility of water and soil, so intensive feeding is done with
cheap trash fish. The final stage in the evolution is the floating cage
in which the fish are very intensively grown, and fed artificially, and
in which the water plays no part except to provide living space and
oxygen, and to remove waste products. With this method the natural
fertility of the estuary is not used.
Pillay (1966a) has published a useful bibliography of brackishwater fish culture.
I n this article, the culture of molluscs will not be treated, but only
that of fish and prawns.
B. Definition of estuaries as sites for fish farms
A recent definition of an estuary is “ a semi-enclosed coastal body
of water having a free connection with the sea, and within which the
sea water is measurably diluted with fresh water derived from land
drainage. . . . Associated with an estuary are transition zones, salt
marshes, coastal marshes, intertidal areas, sounds, and other coastal
water areas, plus the vital tidal fresh water habitats above the upper
limits of salt water intrusion, so important as spawning and nursery
areas for many anadromous species ” (quoted by Smith, 1966).
A rather wider definition of an estuary is, “ a n environmental
system consisting of the estuary and those transitional areas constantly
influenced or affected by water from the estuary ”. For example, fine
silt carried down by a river may be deposited by coast-wise currents
beyond the strict geographical limits of the estuary, and may lead to
accretion of land where conditions are suitable.
These definitions are more applicable to north temperate conditions
than t o tropical or sub-tropical conditions. Day (1967) describes the
St. Lucia Estuary in South Africa. I n summer, there are floods and
low salinities, while in winter the rivers cease to flow, and the headwaters of the estuary may then become more saline than the sea.
d’Ancona (1954) writes that all littoral lakes undergo variations in
salinity due to fresh water run-off and evaporation. Hardenberg (1950)
thought that in the conditions of south-east Asia estuarine conditions
C. F. HICKLING
though the results are impressive. The barrier of posts, and the traps,
are derived from a very primitive fishing device called a fish fence. A
further evolution is the now-superseded semi-arginate valle of the
north Adriatic, in which the fish were enclosed within palisades to
grow ; and also the great pounds, made largely of netting supported on
concrete piling, in which the Japanese cultivate intensively the yellowtail (Seriola), puffer (Fugu), and prawn. The free access of water allows
a far greater weight of fish than could possibly be supported by the
natural fertility of water and soil, so intensive feeding is done with
cheap trash fish. The final stage in the evolution is the floating cage
in which the fish are very intensively grown, and fed artificially, and
in which the water plays no part except to provide living space and
oxygen, and to remove waste products. With this method the natural
fertility of the estuary is not used.
Pillay (1966a) has published a useful bibliography of brackishwater fish culture.
I n this article, the culture of molluscs will not be treated, but only
that of fish and prawns.
B. Definition of estuaries as sites for fish farms
A recent definition of an estuary is “ a semi-enclosed coastal body
of water having a free connection with the sea, and within which the
sea water is measurably diluted with fresh water derived from land
drainage. . . . Associated with an estuary are transition zones, salt
marshes, coastal marshes, intertidal areas, sounds, and other coastal
water areas, plus the vital tidal fresh water habitats above the upper
limits of salt water intrusion, so important as spawning and nursery
areas for many anadromous species ” (quoted by Smith, 1966).
A rather wider definition of an estuary is, “ a n environmental
system consisting of the estuary and those transitional areas constantly
influenced or affected by water from the estuary ”. For example, fine
silt carried down by a river may be deposited by coast-wise currents
beyond the strict geographical limits of the estuary, and may lead to
accretion of land where conditions are suitable.
These definitions are more applicable to north temperate conditions
than t o tropical or sub-tropical conditions. Day (1967) describes the
St. Lucia Estuary in South Africa. I n summer, there are floods and
low salinities, while in winter the rivers cease to flow, and the headwaters of the estuary may then become more saline than the sea.
d’Ancona (1954) writes that all littoral lakes undergo variations in
salinity due to fresh water run-off and evaporation. Hardenberg (1950)
thought that in the conditions of south-east Asia estuarine conditions