238
Aquaculture of Cyprinids
bodies, though to a lower extent than Zoopl. larvae : St 82 : 0,54—0,84, St E:
0.72—1.32, St 83 : 0.52—0.75 cal/larva/d; St P was best : 1.09—3.15 cal/larva/
d.
The efficiencies of St P were fairly high (K
15.5—24.32, U_1 31.9—44.7Z),
being only slightly lower than those of Zoopl. &K1 25.2—36.5%,
43.6—58.4Z)
however, the intake of St P was lower than that of zooplankton, C being 7.1—
13.0 and
11.5 —94.8 cal/larva/d, respectively. Enzymic or heat pretreatment
of
starters
of
the same
composition / St E and St T vs. St 82/ failed to
improve the feeding results.
THE EFFECT OF DIPTEREXR ON THE GROWTH, FEEDING AND SURVTVAL OF PIKE PERCH
LARVAE
(Stizostedion lucioperca) IN NURSING FONDS. L.J.K. KLEVN and J. VERREWi.
Depæuüwemî 05 F1/Sh CuÆÆu/œ and IyzÆand FÂ/ShQ/LCQA, AgæécuÆÆu/œ
P.O. 5.358, Wag2nÀngen, THE NETHERLANDS.
Dipterex R, a trichloorfon containing pesticide, and a short water filling
period were compared in eight pike perch nursing ponds as possible means to
improve the food conditions for the fish larvae. Application of 1 mg/l of
Dipterex resulted in a significant higher yield of fingerlings. The mean
individual weight of the fingerlings was significant lower in Dipterex
treated ponds than in non—treated ponds. However, the growth rate were not
affected by the treatments, indicating that the size differences at harvest
were
caused by differences in the culture period. The higher survival rates
in Dipterex treated ponds were positively correlated with the percentage of
Rotatoria and Nauplii in the nursing ponds during the first week of the
culture period.
AN "OPTIMAL FORAGING" APPROACH TO REARING CARP LARVAE
:
EXPERIMENTS WITH THE
COMMON CARP, Cyprinus carpio. T.R. RÀO and 2.3. KHÀÛKÀ, DcpaätmQnt 06 Zoo£ogy
05 ÜQKËÎ, DEÏHÏ 710007, INDIA.
Our incomplete knowledge of the food requirements of carp fry, particularly
during the first few days after hatching, is generally reflected in the poor
survival rates of the fry in hateheries and nurseries. The theory of "optimal
foraging strategy" developed by ecologists was found to be a fruitful approach
to
understanding the optimal diets of carp larvae during the stage when they
can
utilize live food items only or fare poorly on artificial diets. We con—
ducted experiments on prey selection by common carp larvae at different ages,
using as prey different sizes, types and densities of zooplankton (the roti—
fer Brachionus patulus, the Cladocerans Macrothrix chevrauxi and Daphnia
tibetana). Larval mouth size, prey size, prey encounter rate, and prey—han—
dling time were measured. When the larvae were offered prey of different
sizes, they were eaten in the same ratio as encountered when prey density
was
low; at higher prey density however, the unprofitable prey sizes were
dropped sequentially from the diet in accordance with the reactive—field
volume model
(Werner and Hall,
1974) and the apparent size selection model
(O‘Brien ÊÈ.Êl= 1976). Optimal prey sizes for larvae at ages 8, 20, and 30
days were 83, 756, and 1570 pm, respectively. Such information can be very
useful
in selecting the right size and density of live—food items for stockËng
in
nursery ponds and in preparing artificial diets acceptable to carp
ry.
Aquaculture of Cyprinids
bodies, though to a lower extent than Zoopl. larvae : St 82 : 0,54—0,84, St E:
0.72—1.32, St 83 : 0.52—0.75 cal/larva/d; St P was best : 1.09—3.15 cal/larva/
d.
The efficiencies of St P were fairly high (K
15.5—24.32, U_1 31.9—44.7Z),
being only slightly lower than those of Zoopl. &K1 25.2—36.5%,
43.6—58.4Z)
however, the intake of St P was lower than that of zooplankton, C being 7.1—
13.0 and
11.5 —94.8 cal/larva/d, respectively. Enzymic or heat pretreatment
of
starters
of
the same
composition / St E and St T vs. St 82/ failed to
improve the feeding results.
THE EFFECT OF DIPTEREXR ON THE GROWTH, FEEDING AND SURVTVAL OF PIKE PERCH
LARVAE
(Stizostedion lucioperca) IN NURSING FONDS. L.J.K. KLEVN and J. VERREWi.
Depæuüwemî 05 F1/Sh CuÆÆu/œ and IyzÆand FÂ/ShQ/LCQA, AgæécuÆÆu/œ
P.O. 5.358, Wag2nÀngen, THE NETHERLANDS.
Dipterex R, a trichloorfon containing pesticide, and a short water filling
period were compared in eight pike perch nursing ponds as possible means to
improve the food conditions for the fish larvae. Application of 1 mg/l of
Dipterex resulted in a significant higher yield of fingerlings. The mean
individual weight of the fingerlings was significant lower in Dipterex
treated ponds than in non—treated ponds. However, the growth rate were not
affected by the treatments, indicating that the size differences at harvest
were
caused by differences in the culture period. The higher survival rates
in Dipterex treated ponds were positively correlated with the percentage of
Rotatoria and Nauplii in the nursing ponds during the first week of the
culture period.
AN "OPTIMAL FORAGING" APPROACH TO REARING CARP LARVAE
:
EXPERIMENTS WITH THE
COMMON CARP, Cyprinus carpio. T.R. RÀO and 2.3. KHÀÛKÀ, DcpaätmQnt 06 Zoo£ogy
05 ÜQKËÎ, DEÏHÏ 710007, INDIA.
Our incomplete knowledge of the food requirements of carp fry, particularly
during the first few days after hatching, is generally reflected in the poor
survival rates of the fry in hateheries and nurseries. The theory of "optimal
foraging strategy" developed by ecologists was found to be a fruitful approach
to
understanding the optimal diets of carp larvae during the stage when they
can
utilize live food items only or fare poorly on artificial diets. We con—
ducted experiments on prey selection by common carp larvae at different ages,
using as prey different sizes, types and densities of zooplankton (the roti—
fer Brachionus patulus, the Cladocerans Macrothrix chevrauxi and Daphnia
tibetana). Larval mouth size, prey size, prey encounter rate, and prey—han—
dling time were measured. When the larvae were offered prey of different
sizes, they were eaten in the same ratio as encountered when prey density
was
low; at higher prey density however, the unprofitable prey sizes were
dropped sequentially from the diet in accordance with the reactive—field
volume model
(Werner and Hall,
1974) and the apparent size selection model
(O‘Brien ÊÈ.Êl= 1976). Optimal prey sizes for larvae at ages 8, 20, and 30
days were 83, 756, and 1570 pm, respectively. Such information can be very
useful
in selecting the right size and density of live—food items for stockËng
in
nursery ponds and in preparing artificial diets acceptable to carp
ry.