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The purpose of this study was to evaluate fertilization strategies for
rain-fed ponds based on strategies developed for ponds with regular water
inputs. Rain-fed ponds might be expected to have different fertilization
schedules because the water depth changes with time and evaporation may
concentrate nutrients and metabolites. Four experimental treatments were used:
A) fertilization every two weeks with water replacement, B) fertilization every
two weeks with no water replacement, C) fertilization once at the start of
culture without water replacement, and D) fertilization irregularly when water
nutrient levels declined without water replacement. Fertilization rates were
similar to earlier optimal rates for CRSP ponds. Fish were stocked at 2 per m2
(1600 per pond) and cultured for 150 days. Growth, survival, and yield were
determined, and water quality was evaluated throughout the experiment.
Treatments A and B (regular fertilization with or without water replacement)
resulted in the highest growth rates, with irregular fertilization yielding
lower growth and one fertilization the lowest growth. Survival was not
significantly different among treatments. Several water quality variables,
particularly nitrogen levels, varied among treatments, with A and B having
higher levels than the other treatments. Regularly fertilized ponds with or
without water addition both showed significant accumulation of nutrients over
time, but there was no difference between these treatments. Fertilization
strategies developed for ponds with regulated water depth worked effectively
for ponds with evaporation losses that were not replaced. This study used input
additions on a per areal basis, which were lower (by about one-half) than
inputs would be on a per volume basis since the guidelines were developed for 1
m deep ponds and the study ponds began with water depths at 2.5 m. Growth and
yields were slightly reduced compared to experiments in other pond systems,
probably due to slightly lower nutrient input rates.
The objective of this study was to evaluate caging densities and pond
loading rates for tilapia caged and fed in semi-intensive ponds with small
tilapia at large. Such a system could be an effective means to produce large
tilapia efficiently, as well as produce smaller tilapia and keep culture
facilities at a reasonable level. Caged tilapia were held at five densities;
16, 32, 64, 128, and 256 fish per m3 cage. Pond loading rates were 2 tilapia
per m2 (626 fish per pond) and caged tilapia were loaded at two rates:
224 or 560 caged fish per pond. Growth, survival, and yield of tilapia in cages
and in ponds were estimated over 90 days of culture. Growth rates of tilapia in
cages were similar regardless of density, and average tilapia size at harvest
was 700g. Survival differed significantly with cage density, with fish from
16-64 per cage showing no differences in mortality, while fish at higher
densities had very high morality rates. Fish at large in the ponds showed
similar growth and mortality rates to other culture systems, even though the
only source of nutrients was through the unused feed, fecal matter, and
excretory products of the caged fish. Water quality did not deteriorate within
the ponds at either loading rate. Cage stocking densities of 64 fish per
m3 were most reasonable for tilapia culture, and resulted in good survival and
significant growth. The results on pond loading rates were not clear, since
significant mortality occurred for some caged fish in the high loading ponds,
yet it is unclear if the problem was a cage effect or a pond effect.
The purpose of this experiment was to determine the upper limits to
tilapia production utilizing supplemental feeds. In order to test this, fish
were stocked at 3, 6, and 9 fish per m2. These fish were supplementally fed to
satiation during culture for
146 days. Growth, survival, yield, and water quality were evaluated during the
experiment. Growth continued in a linear fashion throughout the experiment, and
density dependent growth occurred with the lowest density having significantly
higher growth rate than the intermediate density, and with the highest density
having the lowest growth rate. Survival also differed significantly among
treatments, with lowest survival at highest density. Feeding rate averaged 1.9
%BW/d and was not significantly different among treatments. Feed conversion
rate averaged 0.89 and was also similar among treatments. Water quality was not
significantly different among treatments, and did not deteriorate during
culture. The highest growth rate and survival occurred in low density ponds,
yet there was no measured deterioration in water quality even in higher density
ponds. It is unclear whether the higher density ponds had behavioral
differences among tilapia to result in lower growth and higher mortality, or
whether water quality actually differed but was not measured with our sampling
regime. At present, the best system seems to be culture at 3 fish per m2 with
intensive feeding.
CRSP research in Thailand has concentrated on the dynamics of
Oreochromis niloticus monocultures. As Oreochromis niloticus is
primarily a planktivore, the addition of the benthic detritivore Cyprinus
carpio was hypothesized to lead to increased system productivity through
the conversion of currently unutilized benthic matter into fish flesh.
A five-month experiment was conducted in
earthen ponds of 200 m2 surface area at the Asian Institute of Technology.
Fifteen ponds were allocated to five treatments: carp stocking densities of 0,
0.1, 0.3, 0.5, and 0.7 fish/m2, with three replicates, in three blocks which
represented common carp of different sizes at stocking. Ponds were fertilized
weekly with chicken manure, urea, and TSP.
Only preliminary results are available for this experiment. Tilapia growth was
slow and uniform across blocks and treatments, likely because larger fish
(>25 g/fish) had been erroneously selected from the batch to stock a
different experiment before this experiment was stocked. Carp growth was
extremely sensitive and inversely related to stocking density; carp of initial
(pond mean) weights
11-40 g/fish grew to pond means 41-270 g/fish during five months.
Through the first half of the experiment, there was little indication of
treatment-related differences in water quality except in measures of turbidity.
Total suspended solids were markedly lower in ponds without carp. The
parameters chosen for this experiment were appropriate to produce
treatment-related differences in suspended solids and to reveal the density
dependence of carp growth.
In regions of large seasonal differences in rainfall, many farms have
reservoir ponds. These can be used in addition for fish culture, but are often
deeper (2-3 m) than those in which the CRSP fertilization protocols and other aspects
of pond dynamics have been studied. The greater depth potentiates more severe
density stratification than is common in shallower ponds, and therefore less
often dissolved by convective overturn at night or by wind-induced mixing. This
makes oxygen depletion of the hypolimnion more likely. This study attempted to
describe and quantify diel cycles of temperature and DO stratification in the
deep rain-fed ponds of current focus in the AIT Outreach activities, and to
compare these patterns with those of shallower ponds typical of CRSP
experiments.
Ponds of 800 m2 area and 2.5 m depth at the Huay Luang station were monitored
during fish growth experiments; diel cycles of temperature and DO were recorded
with an automated monitoring system. During sunny, dry season days, the pond
had a slightly deeper mixed layer (at least 35 but much less than 75 cm) than
is characteristic of ponds at the more sheltered AIT site. The bottom water
below 2 m depth was almost completely isolated from the upper water, receiving
only minimal transport of oxygen from above. During the rainy season, the
isolation below 200 cm was maintained even through a dark rainy day. These
assessment techniques showed that active mixing may be necessary to maintain
deep ponds as suitable culture environments for some animal species; the
techniques can be used to assess low-cost mixing strategies.
Rates of exchange of dissolved oxygen and carbon dioxide between pond
waters and the atmosphere are often significant components of a pond's
budget for these materials. Oxygen exchange is routinely estimated in
free water studies, but far less attention has been given to diffusion of
carbon dioxide, which may, however, be significant. The objectives of this work
were to quantify the rates of exchange of carbon dioxide between pond water and
the atmosphere in fertile earthen ponds, and to elucidate major factors which
determine these rates. An analysis of data from the University of Hawaii pond
research facility in the U.S. was made, detailing the diel cycles of total
carbon dioxide, the component species aqueous ("free") carbon dioxide, net
changes in CO2 concentrations, and wind speed.
Total CO2 concentrations varied little during the day, but showed a perceptible
dip during mid-day, reflecting photosynthetic uptake. Wind speeds at 0.5 m
above water surface ranged from about 0.6 to 1.8 m/s, with the windiest periods
concentrated into daylight hours. The free CO2 fraction of total CO2 (about 1%
of the total) varies in parallel with total CO2, but accounted for only about
25% of the diel variation in the total CO2. Multiple regression analysis showed
that the concentration of free CO2 and wind speed together accounted for 81% of
the variation in the diffusion rates during this diel cycle. The net rates of
change in CO2 concentration during the 30 minute sampling intervals contributed
no significant effect to diffusion rates and did not add to the percentage of
the diel variation in diffusion rates which was explained by the other two
factors. Model prediction of diffusion rates thus requires only observed
concentrations and wind speed, though photosynthetic demand can be the primary
determinant of concentrations under some conditions.
Three strains of Oreochromis niloticus were grown in ponds
fertilized with 4 kg N/ha/d plus 0.8 kg
P/ha/d to compare growth performance. The FAC strain were descendants of O.
niloticus imported to the Philippines in the 1970s and kept at the
Freshwater Aquaculture Center (FAC). The Thai strain were descendants of fish
imported from Thailand in the 1980s and maintained by the Bureau of Fisheries
and Aquatic Resources and ICLARM. The Egypt-Swansea strain originated from fish
collected from Lake Manzala in 1979. These fish were used to create a
laboratory strain at University College of Swansea during the 1980s and were
subsequently transferred to FAC in 1989. Extrapolated yields of the Thai and
Egypt-Swansea strains were not significantly different from each other and
averaged approximately 5,000 kg/ha/yr. The average extrapolated yield of the
FAC strain was only 2,389 kg/ha/yr reflecting the probable introgression of
O. mossambicus.
Additionally, the yield of Egypt-Swansea fish grown in ponds fertilized at 2 kg
N/ha/d plus 0.4 kg
P/ha/d was compared to yield of fish grown at
4 kg N/ha/d. No significant difference was observed.
The objective of this study was to assess the effect of other fish
species on the water quality and yield of tilapia and of all fish in deep,
rain-fed ponds. The experimental design included three fish stocking treatments
with four replicates per treatment. Sex-reversed Oreochromis niloticus
were stocked at
2 fish/m2 into 12 earthen ponds at Udorn. Stocking occurred in late June 1995.
They are to be cultured for five months, with a final harvest in late November
1995. Three treatments differed in stocking density of common carp Cyprinus
carpio, with 0 carp in treatment 1,500 carp per hectare in treatment 2, and
1,000 carp per hectare in treatment 3. Carp were stocked at 500 g in size. All
treatments will receive fertilizer application at the optimum frequency and
rate, which is 70 kg/ha/wk of chicken manure, with sufficient urea and
phosphorus added to provide
0.5 g/m2/d N and 0.125 g/m2/d P. Ponds were filled initially to 2.5 m,
further water addition will only occur by rainfall. Standard protocols will be
utilized for physical and chemical monitoring of ponds with the following
exceptions. Diurnal sampling will be done every month at 4 depths
(stratification can be quantified by top to bottom differentials in O2 or
temperature). Secchi disk depth will also be measured in diurnal analyses.
Evaporation rate will be measured weekly. Final comparisons will be made to
determine if the addition of carp influenced the stratification or turbidity of
these ponds, as well as the yield of tilapia.
This study was initiated by holding two workshops with 10 fisheries
officers from four provinces in Northeast Thailand, including Udorn, Nong Khai,
Sakon Nakhon, Loei. Each provincial fisheries officer solicited four to six
small-scale farmers from his or her province to participate in the high input
green water scheme recommended by AIT-CRSP program. Biologists from Udorn
station monitored the farmers activities.
Most farmers started their growout at the beginning of the rainy season in May
and June 1995. There were complications getting production data because most
farmers do not harvest their fish in one harvest; instead they catch fish in
small numbers upon demand by local consumers or simply for their own
consumption. In addition, the farmers mostly keep their fish until ponds dry
out during the dry season. However, preliminary feedback from the farmers was
very positive.
We will follow up to collect production data. We are planning to expand the
number of farmers.
Extrapolation, particularly scaling upward the results of trials in
small impoundments to production scale ponds, is a classical and unsolved
problem in aquaculture. Our interest here was not in solving the lager problem,
but rather to examine earthen ponds of available different sizes for potential
effects on CRSP experimental results at the Asian Institute of Technology
(AIT). A five month experiment was conducted in 11 earthen ponds of four
different surface areas (approximately 200, 380, 610, and
1390 m2) with triplicate ponds of each size. Ponds were stocked with
sex-reversed fingerlings of Nile tilapia (Oreochromis niloticus) at 2
fish per m2. Ponds were fertilized with chicken manure at 250 kg dry
matter/ha/wk supplemented with urea and TSP to attain rates of 35 kg N/ha/wk
and 7 kg P/ha/wk. Water sampling and analysis were performed according to
standard protocols, with detailed water sampling/analyses conducted every
month. Extrapolated yields ranged from 1,921 to
8,631 kg/ha/yr. Single-factor ANOVA showed no significant relationship between
yield and pond size. This means that areal fish yields may be expected to
increase as ponds become larger. However, extrapolation to pond sizes beyond
the largest used here is unwarranted.
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The Pond Dynamics/Aquaculture CRSP is funded under USAID Grant No. LAG-G-00-96-90015-00
and by
the participating US and Host Country institutions.
Questions for or about the Aquaculture CRSP? Comments about this site? Email ACRSP@oregonstate.edu.
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