ESTUARINE FISH FARMING
151
or more changes of water. As he writes, there are in front of him three
small Crenimugil labrosus which have already spent eight months in tap
water and are growing well. But this species can be transferred straight
back from tap water to full sea water, showing that the grey mullets
are true sea fish. Morovic and Sabioncello (1965) found the same result.
However, grey mullet artificially transferred to fresh water seem more
liable to parasitic infection than in sea water; Yashouv and BenSchachar (1967) found that keeping the Mugil cephalus in 1 part of
sea water to 9 parts of fresh water protected them : Doroshev (1963)
also found that placing his carp in diluted sea water rid them of infection.
Grey mullet can obtain oxygen from water of low oxygen content
and can survive for long periods in water containing less than 0.5 p.p.m.
dissolved oxygen, but they have no accessory respiratory system and
will die in water totally devoid of oxygen (Thomson, 1966).
B. The natural history of the species
The most important species cultivated in brackish-water f?&&&ms
are :-Milkfish, Chanos chanos (Forsk.) ; Grey mullets, species of Nugil,
Lixa, Crenimugil; Eels, Anguilla spp ; Salmon and Sea Trout, Salmonidae ; Tilapia, chiefly T . mossambica (Peters) ; Penaeid prawns.
Chanos (Fig. 8) is an oceanic fish, which approaches the coasts to
breed, so that the young are soon carried or swim into brackish-water
lagoons, salt creeks, mangrove swamps, and open beaches. Lin (1968)
believes that Chanos follow the Kuroshio Current in scattering schools
north eastward from the Philippines to the coast of Taiwan, and to the
coast of southern Japan, for feeding and spawning. There is no fishery
for the adult Chanos, which can grow to a metre in length. Schuster
(1952) says that no more than a hundred adult specimens are caught
yearly along the coast of Java. He points out that there is some evidence
that the spawning of Chanos takes place twice a year near the Spermonde
Islands, south west of Celebes, among other places. The eggs and larvae
are rarely found (Delsman was able to handle only 20 eggs in many
years of work) ; but the fry, which are about 11-13 mm long appear
in millions on the north coast of Java and Madura. After a stay of
about 10 days in the coastal waters, the fry disappear, and adolescent
Chaws are never observed in coastal waters even though there is an
intensive fishery there. A few which enter the fresh water Temp6 Lake
in Celebes grow to adolescence (at 28 inches) in 2-3 years. So there is
still a gap in our knowledge of the natural history of this fish. Luckily,
Chanos stay in coastal waters long enough for the capture of the fry
needed for the important pond cultures of the Philippines, Taiwan,
151
or more changes of water. As he writes, there are in front of him three
small Crenimugil labrosus which have already spent eight months in tap
water and are growing well. But this species can be transferred straight
back from tap water to full sea water, showing that the grey mullets
are true sea fish. Morovic and Sabioncello (1965) found the same result.
However, grey mullet artificially transferred to fresh water seem more
liable to parasitic infection than in sea water; Yashouv and BenSchachar (1967) found that keeping the Mugil cephalus in 1 part of
sea water to 9 parts of fresh water protected them : Doroshev (1963)
also found that placing his carp in diluted sea water rid them of infection.
Grey mullet can obtain oxygen from water of low oxygen content
and can survive for long periods in water containing less than 0.5 p.p.m.
dissolved oxygen, but they have no accessory respiratory system and
will die in water totally devoid of oxygen (Thomson, 1966).
B. The natural history of the species
The most important species cultivated in brackish-water f?&&&ms
are :-Milkfish, Chanos chanos (Forsk.) ; Grey mullets, species of Nugil,
Lixa, Crenimugil; Eels, Anguilla spp ; Salmon and Sea Trout, Salmonidae ; Tilapia, chiefly T . mossambica (Peters) ; Penaeid prawns.
Chanos (Fig. 8) is an oceanic fish, which approaches the coasts to
breed, so that the young are soon carried or swim into brackish-water
lagoons, salt creeks, mangrove swamps, and open beaches. Lin (1968)
believes that Chanos follow the Kuroshio Current in scattering schools
north eastward from the Philippines to the coast of Taiwan, and to the
coast of southern Japan, for feeding and spawning. There is no fishery
for the adult Chanos, which can grow to a metre in length. Schuster
(1952) says that no more than a hundred adult specimens are caught
yearly along the coast of Java. He points out that there is some evidence
that the spawning of Chanos takes place twice a year near the Spermonde
Islands, south west of Celebes, among other places. The eggs and larvae
are rarely found (Delsman was able to handle only 20 eggs in many
years of work) ; but the fry, which are about 11-13 mm long appear
in millions on the north coast of Java and Madura. After a stay of
about 10 days in the coastal waters, the fry disappear, and adolescent
Chaws are never observed in coastal waters even though there is an
intensive fishery there. A few which enter the fresh water Temp6 Lake
in Celebes grow to adolescence (at 28 inches) in 2-3 years. So there is
still a gap in our knowledge of the natural history of this fish. Luckily,
Chanos stay in coastal waters long enough for the capture of the fry
needed for the important pond cultures of the Philippines, Taiwan,