166
C. F. HICKLING
purpose as will be shown later. But in Taiwan, experiments done by
Tang and Huang (Lin, 1968) on the digestibility of crude protein, crude
fat, nitrogen-free extract, and fibre of four groups of algae, namely
Chaetomorpha, phytoflagellates, diatoms, and fresh blue-green algae,
showed that fresh diatoms had the highest coefficient of digestion
of protein (87%), next came phytoflagellates (81%), then blue-green
algae (69%) and finally, decayed Chaetomorpha (66%). However, fresh
Chaetomorpha had a digestion coe%cient for crude protein of only 6%)
and the fresh filaments have a tough and wiry impenetrable cell wall.
According to Villadolid and Villaluz, quoted by Lin (1968), Chanos,
feeding on filamentous algae, have a poor rate of food conversion,
namely, 33 to 87 parts of Enteromorpha or Cladophora, to make one part
of fish. This compares with a conversion rate of 12.5 to 1 in algal
pasture consisting mainly of blue-greens (Tang and Chen, 1966), and
Schuster (1952) gives an approximate conversion rate of 25-35 lb
wet weight of algae to produce 1 lb of fish.
These views are criticized by Schuurman (1956), who carried out
three experiments to test the food preferences of Chanos. He quotes
the results of Markus, who showed that the rate of production of
Chanos was only 14-24 kglhectare in two ponds with very few filamentous algae, was 80-108 kglhectare where filamentous algae were
moderately abundant ; but as high as 170-270 kglhectare in four
ponds in which filamentous algae were abundant. The species of algae
are not given, but presumably were filamentous green algae.
Schuurman divided a single rectangular pond into 24 compartments
by low dykes, all compartments irrigated by water taken from the same
canal. As this pond had been in use for seven years previously, it
would have a reasonably homogeneous bottom soil. The salinity of the
24 small ponds, each having an area of about 800 m2, did not vary
significantly from 30x0 throughout the experiment.
He randomized three treatments among the 24 ponds as follows:
(i) Undisturbed growth of filamentous algae.
(ii) Filamentous algae growing in the pond raked together and
heaped into mounds, so as to compost slowly and act as green manure,
and
(iii) Filamentous algae removed repeatedly from the pond.
The ponds were each stocked with 25 fingerlings of Chanos of 14 g
weight. After 95 growing days, it was found that though the rate of
survival was not affected, the fish in treatment (i) had grown by 226 g,
those in (ii) by 163 g, and those in (iii) by 152 g.
I n the second and third experiments, which were run simultaneously,
the 24 small ponds were divided into two lots of 12 ponds each. I n one
C. F. HICKLING
purpose as will be shown later. But in Taiwan, experiments done by
Tang and Huang (Lin, 1968) on the digestibility of crude protein, crude
fat, nitrogen-free extract, and fibre of four groups of algae, namely
Chaetomorpha, phytoflagellates, diatoms, and fresh blue-green algae,
showed that fresh diatoms had the highest coefficient of digestion
of protein (87%), next came phytoflagellates (81%), then blue-green
algae (69%) and finally, decayed Chaetomorpha (66%). However, fresh
Chaetomorpha had a digestion coe%cient for crude protein of only 6%)
and the fresh filaments have a tough and wiry impenetrable cell wall.
According to Villadolid and Villaluz, quoted by Lin (1968), Chanos,
feeding on filamentous algae, have a poor rate of food conversion,
namely, 33 to 87 parts of Enteromorpha or Cladophora, to make one part
of fish. This compares with a conversion rate of 12.5 to 1 in algal
pasture consisting mainly of blue-greens (Tang and Chen, 1966), and
Schuster (1952) gives an approximate conversion rate of 25-35 lb
wet weight of algae to produce 1 lb of fish.
These views are criticized by Schuurman (1956), who carried out
three experiments to test the food preferences of Chanos. He quotes
the results of Markus, who showed that the rate of production of
Chanos was only 14-24 kglhectare in two ponds with very few filamentous algae, was 80-108 kglhectare where filamentous algae were
moderately abundant ; but as high as 170-270 kglhectare in four
ponds in which filamentous algae were abundant. The species of algae
are not given, but presumably were filamentous green algae.
Schuurman divided a single rectangular pond into 24 compartments
by low dykes, all compartments irrigated by water taken from the same
canal. As this pond had been in use for seven years previously, it
would have a reasonably homogeneous bottom soil. The salinity of the
24 small ponds, each having an area of about 800 m2, did not vary
significantly from 30x0 throughout the experiment.
He randomized three treatments among the 24 ponds as follows:
(i) Undisturbed growth of filamentous algae.
(ii) Filamentous algae growing in the pond raked together and
heaped into mounds, so as to compost slowly and act as green manure,
and
(iii) Filamentous algae removed repeatedly from the pond.
The ponds were each stocked with 25 fingerlings of Chanos of 14 g
weight. After 95 growing days, it was found that though the rate of
survival was not affected, the fish in treatment (i) had grown by 226 g,
those in (ii) by 163 g, and those in (iii) by 152 g.
I n the second and third experiments, which were run simultaneously,
the 24 small ponds were divided into two lots of 12 ponds each. I n one