ESTUARINE FISH FARMING
167
series, small Chanos of 1 4 g weight were stocked and in the other,
larger Chanos of 200 g. The biomass of fish stocked in the one series
was 350 g, and in the other 4 000 g. The results were the same as
in the first experiment. Schuurman sums them up by saying that they
give no evidence that filamentous algae are only of value as food for
Chanos when in a decaying state, and that average growth was best in
the ponds where the filamentous algae grew undisturbed and therefore
in a living condition.
Another point which seems t o come out of these instructive experiments is the good growth shown by Chanos, both large and small, in
the ponds from which the growing filamentous algae were repeatedly
removed. The growth observed is hardly inferior to that in which the
algae were raked together, and better than half that in the undisturbed
ponds. Evidently, a substantial part of the observed growth was at
the expense of organisms not directly associated with the green algaeeven the very high biomass of the third experiment (20 g/m2) increased by 12 g/m2. It would have been interesting if Schuurman had
examined the stomach contents of these fish.
I n Hawaii, Hiatt (1944) found that, while the small Chanos ate
mostly blue-green algae and benthic diatoms, larger fingerlings of 1140 cm ate up t o 20% of green algae, 25% of detritus and 43% of
diatoms.
However there seems to be agreement that the blue-green algal felt,
with its associated flora and fauna, is the best food for the young fry
of Chanos. This gelatinous mixture is called lab-lab in the Philippines,
and tai-ayer in Indonesia. It is carefully cultivated in the fry ponds
and success in the rearing of the fry is proportional to success in raising
an algal felt which will sustain the growth of the fry to fingerling size.
There are many species of grey mullet, but they all seem t o have the
same feeding habits. By far the most important is the circumtropical
striped grey mullet, Mugil cephalus L. Grey mullet have a filtering
mechanism (Gunther, 1861 ; Pillay, 1953), which can reject large
particles through the mouth, while filtering off small particles on the
gill-rakers. I n those species studied, detritus plays a large part in the
composition of the food, together with plant and small animal material.
Accounts of the gut contents of Chanos do not mention the presence
of abundant soil and grit, but this is always present in the gut of the
grey mullets. Because these fish have no masticating organs, the soil
ingested may act as a grinding paste (Odum, 1968). When forced along
the gut by the very muscular gizzard, this soil helps to triturate the
food and so expose it to the action of the digestive enzymes.
Ilin (1954) states that in the Black Sea limans, singil (Liza aurata),
167
series, small Chanos of 1 4 g weight were stocked and in the other,
larger Chanos of 200 g. The biomass of fish stocked in the one series
was 350 g, and in the other 4 000 g. The results were the same as
in the first experiment. Schuurman sums them up by saying that they
give no evidence that filamentous algae are only of value as food for
Chanos when in a decaying state, and that average growth was best in
the ponds where the filamentous algae grew undisturbed and therefore
in a living condition.
Another point which seems t o come out of these instructive experiments is the good growth shown by Chanos, both large and small, in
the ponds from which the growing filamentous algae were repeatedly
removed. The growth observed is hardly inferior to that in which the
algae were raked together, and better than half that in the undisturbed
ponds. Evidently, a substantial part of the observed growth was at
the expense of organisms not directly associated with the green algaeeven the very high biomass of the third experiment (20 g/m2) increased by 12 g/m2. It would have been interesting if Schuurman had
examined the stomach contents of these fish.
I n Hawaii, Hiatt (1944) found that, while the small Chanos ate
mostly blue-green algae and benthic diatoms, larger fingerlings of 1140 cm ate up t o 20% of green algae, 25% of detritus and 43% of
diatoms.
However there seems to be agreement that the blue-green algal felt,
with its associated flora and fauna, is the best food for the young fry
of Chanos. This gelatinous mixture is called lab-lab in the Philippines,
and tai-ayer in Indonesia. It is carefully cultivated in the fry ponds
and success in the rearing of the fry is proportional to success in raising
an algal felt which will sustain the growth of the fry to fingerling size.
There are many species of grey mullet, but they all seem t o have the
same feeding habits. By far the most important is the circumtropical
striped grey mullet, Mugil cephalus L. Grey mullet have a filtering
mechanism (Gunther, 1861 ; Pillay, 1953), which can reject large
particles through the mouth, while filtering off small particles on the
gill-rakers. I n those species studied, detritus plays a large part in the
composition of the food, together with plant and small animal material.
Accounts of the gut contents of Chanos do not mention the presence
of abundant soil and grit, but this is always present in the gut of the
grey mullets. Because these fish have no masticating organs, the soil
ingested may act as a grinding paste (Odum, 1968). When forced along
the gut by the very muscular gizzard, this soil helps to triturate the
food and so expose it to the action of the digestive enzymes.
Ilin (1954) states that in the Black Sea limans, singil (Liza aurata),