402
Aquacu£fwe of
2) Polyculture of Tilapia nilotica and carps in cages in Laguna de Bay.
Tilapia nilotica fingerlings were grown in polyculture with different carps
species (silver, bighead and common carp) in 5 X 10 X 3 m B—net cages in
Laguna de Bay at a stocking density of 38 fish/m2 and at a ratio of 30 Tila—
pia, 3 silver carp, 2.5 bighead carp and 2 common carp. Selective harvesting
(with replenishment) of tilapia was done at intervals of three and six months.
Total harvest of all
species in polyculture was done after one year culture
period. Selective harvesting ("thinning") of marketable sized tilapia
(100 g +) every three months and six months gave an average total biomass
of 5.7 Kg/m2 and 4.7 Kg/m2 respectively at the end of one year. An average
total biomass of 3.6 Kg/m2 tilapia was obtained in the control (one year
culture period without selective harvesting). Growth and production rates
of
the other species in polyculture did not vary significantly in the dif—
ferent
treatments.
Average total biomass of all species in polyculture
ranged from 8.46 Kg/m2 — 12.50 Kg/m2. Survival was highest in bighead carps
(82—94 per cent) followed by silver carps (55—93 per cent) and common carps
(54—63 per cent). The prevailing physico—chemical and biological conditions
with emphasis on the primary and secondary productivity of Laguna de Bay
during the culture period are discussed.
CARP CULTURE TRIALS
IN IRRIGATED RWANDA RICE FIELDS.
(=}. CHODOROWSKA and A.
CHODOROWSKÏ., UnÀUQÆAÂÉË du Québec, MOHÆÆÊŒZ, CANADA.
There are several advantages to Combining fish culture with rice—growing
in irrigated fields (rice—pisciculture): ]) double harvest (rice + fish);
2) better rice harvest (fish excrements enrich the soil); 3) cleaner milieu
(disease—inducing insect larvae are eaten by the fish). The common carp
(Cyprinus carpio) is one of the fish giving the best rice—pisciculture yield.
Carp were reared in all rice fields in Rwanda. Our trials were carried out
in exactly the same conditions as usual rice culture. To receive the fish,
peripheral ditches were dug in each rice field as well as refuge holes in
which the_fish could hide when the rice—field was dried. When the field
contained water,
the fish swam freely over the whole field. The aquatic
fauna of
the rice—field was so rich that it was not necessary to provide
food from
the outside. Young carp of 2 to 4 g were put into the field one
week after the rice was planted when the young shoots were well—rooted.
During rearing (5 to 6 months) the carp easily withstood all the work
required in the field. This period was long enough for the fish to reach
table size, or more than 150 g. The yield obtained (100 to 400 Kg/ha/season)
depended mainly on the initial load and degree of monitoring. A minimum
load
(1000 ind/ha) permitted good growth (up to 500 g) but a relatively low
yield (60—100 Kg/ha/season). When more fish were used (up-to 10 000 ind/ha)
growth was lower (150—200 g) but yield was much higher (up to 400 Kg/ha/Sea”
son). Rice—pisciculture is a very advantageous technique in poor countries
because
the rice—field is increased with no additional investment. A Rwand—
1an
farmer can thus increase rice—field yield by 50%.
THE USE OF CHINESE CARPS TO CONTROL ENVIRONMENTAL CONDITIONS IN PRAWN
(Macrobrachium rosenbergii) FONDS IN HAWAII. DÆ.B.A. COSTA PÏERCE, Aquacuüu&e DQUQ€OpMQWI, P.O. Box 7353, HŒWQKQÀ, KauaÀ,
96714, U.S.A.
Use
of Chinese grass and silver carps in intensive prawn culture as "janitor"
fish to control unwanted macrophytes, overgrowth of phytoplankton, and bui1dUP Of sed1mentg ln prawn ponds has been shown to be an effective and less
costly method of environmental control than traditional methods of heavy
Aquacu£fwe of
2) Polyculture of Tilapia nilotica and carps in cages in Laguna de Bay.
Tilapia nilotica fingerlings were grown in polyculture with different carps
species (silver, bighead and common carp) in 5 X 10 X 3 m B—net cages in
Laguna de Bay at a stocking density of 38 fish/m2 and at a ratio of 30 Tila—
pia, 3 silver carp, 2.5 bighead carp and 2 common carp. Selective harvesting
(with replenishment) of tilapia was done at intervals of three and six months.
Total harvest of all
species in polyculture was done after one year culture
period. Selective harvesting ("thinning") of marketable sized tilapia
(100 g +) every three months and six months gave an average total biomass
of 5.7 Kg/m2 and 4.7 Kg/m2 respectively at the end of one year. An average
total biomass of 3.6 Kg/m2 tilapia was obtained in the control (one year
culture period without selective harvesting). Growth and production rates
of
the other species in polyculture did not vary significantly in the dif—
ferent
treatments.
Average total biomass of all species in polyculture
ranged from 8.46 Kg/m2 — 12.50 Kg/m2. Survival was highest in bighead carps
(82—94 per cent) followed by silver carps (55—93 per cent) and common carps
(54—63 per cent). The prevailing physico—chemical and biological conditions
with emphasis on the primary and secondary productivity of Laguna de Bay
during the culture period are discussed.
CARP CULTURE TRIALS
IN IRRIGATED RWANDA RICE FIELDS.
(=}. CHODOROWSKA and A.
CHODOROWSKÏ., UnÀUQÆAÂÉË du Québec, MOHÆÆÊŒZ, CANADA.
There are several advantages to Combining fish culture with rice—growing
in irrigated fields (rice—pisciculture): ]) double harvest (rice + fish);
2) better rice harvest (fish excrements enrich the soil); 3) cleaner milieu
(disease—inducing insect larvae are eaten by the fish). The common carp
(Cyprinus carpio) is one of the fish giving the best rice—pisciculture yield.
Carp were reared in all rice fields in Rwanda. Our trials were carried out
in exactly the same conditions as usual rice culture. To receive the fish,
peripheral ditches were dug in each rice field as well as refuge holes in
which the_fish could hide when the rice—field was dried. When the field
contained water,
the fish swam freely over the whole field. The aquatic
fauna of
the rice—field was so rich that it was not necessary to provide
food from
the outside. Young carp of 2 to 4 g were put into the field one
week after the rice was planted when the young shoots were well—rooted.
During rearing (5 to 6 months) the carp easily withstood all the work
required in the field. This period was long enough for the fish to reach
table size, or more than 150 g. The yield obtained (100 to 400 Kg/ha/season)
depended mainly on the initial load and degree of monitoring. A minimum
load
(1000 ind/ha) permitted good growth (up to 500 g) but a relatively low
yield (60—100 Kg/ha/season). When more fish were used (up-to 10 000 ind/ha)
growth was lower (150—200 g) but yield was much higher (up to 400 Kg/ha/Sea”
son). Rice—pisciculture is a very advantageous technique in poor countries
because
the rice—field is increased with no additional investment. A Rwand—
1an
farmer can thus increase rice—field yield by 50%.
THE USE OF CHINESE CARPS TO CONTROL ENVIRONMENTAL CONDITIONS IN PRAWN
(Macrobrachium rosenbergii) FONDS IN HAWAII. DÆ.B.A. COSTA PÏERCE, Aquacuüu&e DQUQ€OpMQWI, P.O. Box 7353, HŒWQKQÀ, KauaÀ,
96714, U.S.A.
Use
of Chinese grass and silver carps in intensive prawn culture as "janitor"
fish to control unwanted macrophytes, overgrowth of phytoplankton, and bui1dUP Of sed1mentg ln prawn ponds has been shown to be an effective and less
costly method of environmental control than traditional methods of heavy