154
C . F. HICKLING
water is done very gradually on the commercial scale. The life-history
of these salmonids is too well known to need repetition.
The Tilapias are a successful group of fish, predominantly of
Africa, though one genus, Etroplus, is found in India and Ceylon.
Many of the species inhabit mangrove swamps, where they have to
be adaptable t o rapid changes of salinity, and to tolerate a high salinity.
One species, T . zillii, has been found living in the Red Sea, at salinities
of 40%, (Bayoomi, 1969). By a series of odd chances, one species,
Tilapia mossambica (Fig. 8 ) , has been spread round the world in
tropical and sub-tropical countries. It has a lower temperature limit
of about ll-l2"C, and such countries as Malta and Hong Kong are
near this limit. Attempts to introduce them to Malta have failed, but
they flourish in Israel, California, the southern states of the USA and
the Caribbean. It has proved an embarrassing fish because of its extreme fecundity in fresh water ; but it grows better in brackish water,
not perhaps unexpectedly since that seems to be its natural habitat,
and it has proved to be a real blessing to Java. An account of the
cultivation of Tilapia has been given by Hickling (1963). It is a firstclass food fish, giving lightly-fried fillets of delicate flavour.
The yellow tail, Seriola quinqueradiata (Temminck and Schlegel), is
intensively cultivated, as mentioned above, in cages in Japan. It is
a purely marine fish, and the young are caught at sea among floating
masses of seaweed (Anraku and Azeta, 1966).
Milkfish (Chanos) and grey mullets have feeding habits so similar
that they are in competition when grown together, but over most of
their respective ranges they are separated by their temperature tolerances. According t o Lin (1968) Chanos becomes sluggish at 15-2OoC,
and dies a t 12°C. On the other hand, grey mullet become torpid at
about 5°C and die at prolonged exposure t o 1.5"C (Ilin, 1954 ; Zambribortch, 1962).
The penaeid prawns (Fig. 8) are estuarine dwellers for a part of
their distinctive life-history (Kutukuhn, 1966). Breeding is in the sea
at varying distances from the mainland, and the eggs hatch into small
planktonic nauplii. Rapid development follows through the larval
stages, while the larval prawns are all the while moving in a still unexplained manner towards the mouths of rivers and estuaries and lagoons.
The developing young quickly transform into juvenile prawns in
estuarine conditions. They grow to commercially valuable size in a
few months, and are usually caught in the estuaries on their way back
to the sea to complete the life-cycle. As Kutukuhn says, there is
appreciable variation among penaeids as to the use of estuaries during
their life-history and to the distance out to sea from the estuarine en-
C . F. HICKLING
water is done very gradually on the commercial scale. The life-history
of these salmonids is too well known to need repetition.
The Tilapias are a successful group of fish, predominantly of
Africa, though one genus, Etroplus, is found in India and Ceylon.
Many of the species inhabit mangrove swamps, where they have to
be adaptable t o rapid changes of salinity, and to tolerate a high salinity.
One species, T . zillii, has been found living in the Red Sea, at salinities
of 40%, (Bayoomi, 1969). By a series of odd chances, one species,
Tilapia mossambica (Fig. 8 ) , has been spread round the world in
tropical and sub-tropical countries. It has a lower temperature limit
of about ll-l2"C, and such countries as Malta and Hong Kong are
near this limit. Attempts to introduce them to Malta have failed, but
they flourish in Israel, California, the southern states of the USA and
the Caribbean. It has proved an embarrassing fish because of its extreme fecundity in fresh water ; but it grows better in brackish water,
not perhaps unexpectedly since that seems to be its natural habitat,
and it has proved to be a real blessing to Java. An account of the
cultivation of Tilapia has been given by Hickling (1963). It is a firstclass food fish, giving lightly-fried fillets of delicate flavour.
The yellow tail, Seriola quinqueradiata (Temminck and Schlegel), is
intensively cultivated, as mentioned above, in cages in Japan. It is
a purely marine fish, and the young are caught at sea among floating
masses of seaweed (Anraku and Azeta, 1966).
Milkfish (Chanos) and grey mullets have feeding habits so similar
that they are in competition when grown together, but over most of
their respective ranges they are separated by their temperature tolerances. According t o Lin (1968) Chanos becomes sluggish at 15-2OoC,
and dies a t 12°C. On the other hand, grey mullet become torpid at
about 5°C and die at prolonged exposure t o 1.5"C (Ilin, 1954 ; Zambribortch, 1962).
The penaeid prawns (Fig. 8) are estuarine dwellers for a part of
their distinctive life-history (Kutukuhn, 1966). Breeding is in the sea
at varying distances from the mainland, and the eggs hatch into small
planktonic nauplii. Rapid development follows through the larval
stages, while the larval prawns are all the while moving in a still unexplained manner towards the mouths of rivers and estuaries and lagoons.
The developing young quickly transform into juvenile prawns in
estuarine conditions. They grow to commercially valuable size in a
few months, and are usually caught in the estuaries on their way back
to the sea to complete the life-cycle. As Kutukuhn says, there is
appreciable variation among penaeids as to the use of estuaries during
their life-history and to the distance out to sea from the estuarine en-