Effects of manuring rate on ecology and fish performance in polyculture ponds

Aquaculture. 96 ( 199 1) 119- 138 Elsevier Science Publishers B.V., Amsterdam

119

Effects of manuring rate on ecology and fish performance in polyculture ponds* A. Milste‘in”, A. Alkon”, Y. Avnimelechb, M. Kochbab, G. Hulata” and G. Schroeder” “Fish & Aquaculture Research Station, Dor, M.P. Hof Hacarmel30820. Israel bFaculty ofAgricultural Engineering, Technion, Haifa. Israel (Accepted

I1 October 1990)

ABSTRACT Milstein, A., Alkon, A., Avnimelech, Y., Kochba, M., Hulata, G. and Schroeder, G., 1991. Effects of manuring rate on ecology and fish performance in polyculture ponds. Aquaculture. 96: 119- 138. The present study was designed to quantify the effect of manure application on fish performance and on the ecology of the ponds. Ponds stocked with common carp, tilapia hybrids, silver carp and grass carp received dry chicken manure as the only nutritional input, at three different rates: the standard level used at Dor (50 kg dry matter ha-’ day-‘, increasing by 25 kg ha-’ day-’ every 2 weeks up to 175 kg ha- ’ day- ‘, half of it, and twice the standard. Ecological data included water and sediment parameters, and were analysed through factor analysis and ANOVA. Organic loading increased in two directions, time and treatment. The main sources of variability in the system were related to time. The low effect of treatment was shown in both fish performance and ecological parameters. Of the fish parameters tested, only total yield and common carp growth rate and yield increased with manuring rate. Water quality variability was mainly related to photosynthesis-decomposition balance and algal and bacterial action to metabolize nitrogen, processes which were affected by time and not by manuring rate. A third source of variability in the water column, the respiration of the system, was lower in the treatment with the lower manuring rate. Manuring rate and time strongly affected ecological processes in the sediments: organic loading and anaerobic conditions increased and heterotrophic activity decreased with time and manuring rate, while microbial metabolization of nitrogen decreased with time and increased with manuring rate. The lack of treatment effect on growth and yield of all fish species, except common carp, seems to be related to this difference in the effect of manure level on water and sediment: while common carp feeds on the bottom and is more dependent on feed supplied than the other fish present in the pond, silver carp feeds on phytoplankton in the water body, and tilapia hybrids also favour natural foods of photosynthetic origin.

INTRODUCTION

Fish culture with manure as the main nutritional input is a long-time practice in China (Tang, 1970). The use of manure in fish farming was reviewed by Wohlfarth and Schroeder ( 1979) and Edwards ( 1980), and the advan*This study was supported Countries.

0044-8486/91/$03.50

by the GIARA/Research

0 199 1 -

Programme

for the Benefit of Developing

Elsevier Science Publishers

B.V.

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tages and disadvantages of this practice by Wohlfarth and Hulata ( 1987). Olah ( 1986) reviewed carp production in manured ponds. All these papers are based on bibliographic searches, and no one quotes experiments in which the amount of manure applied was tested. The present study was designed to quantify the effect of manure application. The standard manure regime used at Dor Station (Wohlfarth, 1978) was used as a reference point. The questions asked were: is the standard manuring regime optimal for obtaining maximum fish yield, and how does the amount of manure affect the ecology of the pond? MATERIAL

AND METHODS

The experiment was conducted in 400-m’ earthen ponds, with stone-lined embankments, at the Fish and Aquaculture Research Station, Dor. Ponds were stocked on 21 July 1988 and harvested from l-8 November 1988. All ponds were stocked (per ha) with 3000 common carp (Cyprinus curpio) of 30 g, 6000 hybrid tilapia ( Oreochromis niloticusx 0. aureus) of 14 g, 1000 silver carp (Hypophthalmichthys molitrix) of 54 g, and 500 grass carp (Ctenopharyngodon idellu ) of 37 g, amounting to 10 000 fish ha-’ or initial biomass of 250 kg ha-‘. The ponds were filled with well water at the beginning of the experiment, and further water was supplied only to balance losses by seepage and evaporation (about 1 cm per day). Ponds received dry chicken manure as the only input (Fig. 1) . Treatment M 100 is the standard used at Dor: manure is applied daily (6 days a week), starting at a rate of 50 kg dry matter ha- ’ day- ‘, Manure

Kg dry matter/ha/day

--

M50

ct-

Ml00

4oo-e- MZOO

0 Jul

20

Au9 4

Aug 19

Sep 3

Sep I8

Ott

3

Fig. 1. Manure application during the growing season Arrows point to ecological sampling days.

Ott

I8

(see also figure 5 in Wohlfarth,

1978).

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increasing by 25 kg ha-’ day-’ every 2 weeks until a rate of 175 kg ha-’ day- ’ is reached. This rate is maintained until the end of the growing season ( Wohlfarth, 1978 ) . Due to an error, ponds received a larger amount of manure for about a week at the beginning of October. Treatments M50 and M200 received 50% and 200%, respectively, of the manure input of MlOO. Eight ponds were allocated to each treatment, four of which were sampled for ecological variables. Ecological sampling included water and sediment analyses. Water for chemical analyses was sampled once a week, at noon, after the regular southwestern breeze had mixed the water column. A subsurface sample at the deepest part of each pond was taken. Water was analysed for ammonium nitrogen ( NH4-W ), nitrite+ nitrate (NO,-W) ( NOz was very low all along), total nitrogen (NTOT-W ) , total organic carbon (CORG-W ) , pH and chlorophyll-u (CHLOR). Dissolved oxygen (DOMIN) and temperature were measured early in the morning, just after sunrise. Estimates of heterotrophic digestion in the water (HD-W) and in the sediments (HD-S) were obtained from the changes in weight of cotton strips kept in the ponds (in the water column and in the sediment layer, respectively) for 5 days (Schroeder, 1987). Variable names with a “W” suffix refer to parameters in the water column, while the suffix “S” denotes the sediment. Sediment traps were made of shallow rectangular plastic boxes (22 x 16 x 10 cm) tied to a float for recovery. One to three traps were placed on the bottom of each pond every 2 weeks throughout the experimental period, and left in the pond for 5 days. The purpose of the sediment traps was to collect that fraction of the solid particles of the pond’s bottom which is continually resuspended and are fluctuating between the bottom and the water body. We assume that this is the active fraction of the sediment and that its properties are of significant importance as to the chemical and biological reactions in the pond. Total organic carbon (CORG-S ), total nitrogen exchangeable ammonium (NTOT-S), ammonium nitrogen (NH,-S) and sulphide (SH-S) content of the sedimented matter were determined. Ammonium nitrogen was measured using the automated phenate method and nitrogen in nitrite+nitrate using the automated cadmium reduction method (Standard Methods, 1985 ). Total nitrogen was determined using the persulphate oxidation method (Raveh and Avnimelech, 1979 ) and total organic carbon using a potentiometric method (Raveh and Avnimelech, 1972). Chlorophyll-a was determined using the methanol extraction method (Vollenweider, 1974). Sulphide concentration was measured by the acid dissolution method (Page et al., 1982), and organic nitrogen (NORG-W) was calculated by deducting inorganic nitrogen compounds from total nitrogen. Data were analysed through factor analysis (Seal, 1964; Kim and Mueller, 1978 ) to identify the main processes acting in the system. Differences of the new variables generated by the procedure (Factors) in time and among manuring levels (treatment) were tested through the general linear model

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(GLM ) used as ANOVA. Treatments were compared using the least-square difference (LSD) procedure for multicomparison tests. The analyses were run using the SAS ( 1987 ) package. RESULTS

Fish performance The results of fish performance are presented in Table 1. Survival ranged from 77% for tilapia to 99% for grass carp. Only silver carp survival differed significantly among manure level treatments. It was highest (86%) in M 100 and lowest (68%) in M50, while in M200 it was intermediate (77%) and not significantly different from the other two treatments. Growth rate was similar in the three manure level treatments for all species, except for the common carp, in which it increased from 2.2 g day-’ in M50 to 2.4 g day- ’ in M 100 and 2.8 g day- ’ in M200 (the highest and the lowest being significantly different from one another). Yields of all species varied among manure level treatments, but only in the common carp were the differences statistically signilicant (highest in M200 and lowest in M50, with M 100 being intermediate and not significantly different from either). Total yield was almost identical in M 100 and M200 ( 19.5 kg ha- ’ day- ’ ), but significantly lower in M50 ( 17.3 kg ha- ’ day- ’ ). Water analyses Each water parameter studied shows a different pattern of changes related to time and manure loading (treatment). Water temperature (Fig. 2) was around 30°C till mid-September, decreasing during 1 month to stabilize below 25 oC towards late October-early November. Dissolved oxygen at the early morning critical hours (Fig. 3 ) was between 1.5 and 5 mg l- ‘, generally higher in treatment M50. pH (Fig. 3 ) showed strong variation and differences among treatments at the beginning of the experiment, increasing in all treatments during October. Ammonium concentration (Fig. 4) was generally below 1 ppm, showing fluctuations of the same type in all treatments. Nitrite + nitrate (Fig. 4) increased till late September (mainly in treatment M50) to decrease again towards the end of the experiment. Organic nitrogen (Fig. 4) increased till mid-August, then stayed at about 2.5 ppm, with higher values in October; treatment MS0 had lower values than the others during the whole season. Organic carbon (Fig. 5 ) increased till mid-August, decreased till late September, and increased again towards the end of the season. Chlorophyll (Fig. 5 ) was about 150 pg l- ’ (lower in M200) till early October when it increased to 350 lug l- ‘, to revert to the previous level during the last month. Heterotrophic digestion in the water (Fig. 6 ) was up to 1% per day during the first month, about 2% per day till mid-October, and then decreased again. Factor analysis on water data was run to understand the overall variability

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PONDS

TABLE 1 Survival (O/o). mean daily growth rate (g day-’ ) and yield (kg ha-’ day-’ ) of fish species in the polyculture system (means sharing the same letter are not significantly different at the 0.05 level; A > B; n = 8 ponds per treatment) Treatment

Common carp

Tilapia hybrids

Silver carp

Grass carp

MS0 Ml00 M200

85 A 83 A 86 A

91 A 94 A 88 A

68 B 86 A 77 AB

94 A 99 A 98 A

Total

Survival

Growth M50 Ml00 M200

2.2 B 2.4 AB 2.8 A

1.3 A 1.3 A 1.5 A

6.4 A 6.3 A 6.3 A

1.5 A 1.6 A 1.6 A

M50 Ml00 M200

5.6 B 6.0 AB 6.8 A

6.9 A 1.5 A 1.2 A

4.2 A 5.3 A 4.1 A

0.7 A 0.8 A 0.8 A

Yield 17.3 B 19.6 A 19.5 A

32

1 Jul

20

Fig. 2. Minimum

AUQ 7

Aug

and maximum

28

Sep

temperature

20

Ott

II

act

31

during the growing season.

of the system and identify the main factors acting in it (Table 2). The first factor accounts for 32% of the variance. It shows photosynthesis-decomposition balance in the system: autotrophic activity increased pH through CO1 absorption, raised organic content through growth of algae (CORG-W, NORG-W, CHLOR), and decreased dissolved nutrients through absorption (negative coefficients on NH,-W, NO,-W). Heterotrophic activity decreased pH through respiration and organic detritus particles through decomposition

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5’

D’ 1_ MO 1:

m g / :? I /

c1 F)

i-

RE

7 Jul

25

Aug

15

Sep

5

Ott

4

Fig. 3. Dissolved oxygen at sunrise (top) and pH (bottom) ing season.

Ott

24

in each treatment during the grow-

(CORG-W, NORG-W), while liberating dissolved mineral nitrogen compounds into the water. Since autotrophic and heterotrophic processes affected the measured variables in opposite ways, Factor 1 shows an inverse correlation between them. This factor did not differ among treatments (manure level), and changed with time in a similar way in all of them (Fig. 7 ) . Its value was low at the beginning of the season when algae population (CHLOR), and hence autotrophic processes, were low. The factor had a high value by mid-August, decreasing till late September as manure dose increased. At that time high heterotrophic activity was supported by the man-

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6 .

m

M50

---w-

Ml00

-

M200

7 14_

. .

I

I

N2 0 x w

0

Jul

25

Aug

15

Sep 5

act 4

Ott 24

Fig. 4. Organic nitrogen (top), ammonium (middle) and nitrite + nitrate (bottom) in the water in each treatment during the growing season.

ure together with lowered autotrophic activity. The value of the factor was high during October, when temperature decreased and manure inputs were kept constant and rather lower than before (Fig. 1), indicating that autotrophic processes prevailed over heterotrophic ones. Factor 2, independent of photosynthesis-decomposition balance (Factor 1)) accounts for another 18% of variance. It shows algal (CHLOR) and bacterial (HD-W) action to convert active nitrogen (ammonium) into less active metabolized nitrogen (NORG-W, NO,-W). Through this action the active nitrogen compounds accumulated in the water as algal and microbial

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A. MILSTEIN ET AL.

0 Jul

1

25

I

II

I

Aug

15

’

11

Sep

5

;

Ott

Fig. 5. Chlorophyll (top) and organic carbon (bottom) the growing season.

1

”

4

Ott

24

in the water in each treatment during

biomass increased. The values of this factor increased with time, and showed no differences among treatments (Fig. 7 ) . The three treatments showed a similar behaviour in relation to the first two factors through the growing season. These changes are shown in Fig. 8, in which arrows express the time scale. All points, except c and g, are means of two successive sampling dates with similar values. On the first two sampling dates (a) decomposition dominated over synthesis, since photosynthesis and

MANtiRiNG EFFECTS ON ECOLOGY AND FISH PERFORMANCE IN POLYCULTURE PONDS

. 6

127

M50

-*-

Ml00

-

M200

w Fi

4

% 2

0

6

E s

4

% 2

C Jul

25

Aug

15

Fig. 6. Heterotrophic digestion during the growing season.

Sep 5

Ott

4

Ott

in the water (top) and in sediments

24

(bottom)

in each treatment

nitrogen metabolization were low. In mid-August (b) more nitrogen was metabolized and algal biomass and photosynthesis increased. In late August (c) nitrogen metabolization increased, autotrophic-heterotrophic balance did not change in M 100 and MSO, but decomposition processes were stronger in the most loaded (M200) treatment. In the first half of September (d) decomposition processes dominated in all treatments and less nitrogen was metabolized with increasing manure input level. By late September-early October (e) decomposition processes still prevailed over photosynthesis, but nitrogen metabolization increased. By mid-October ( f ) synthesis processes (photosynthesis and nitrogen metabolization) dominated over decomposition. At

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TABLE 2 Factor analysis on water data, ANOVA of factors and multicomparisons (LSD) between treatments and sampling days (NS= nonsignificant, ***P-c 0.00I;means with equal letters are not significantly different; A < B < ..: n = 136 observations)

CHLOR PH NH,-W NO,-W NORG-W CORG-W HD-W DOMIN

Factor 1

Factor 2

Factor 3

0.49 0.54 - 0.64 -0.57 0.68 0.79 -0.43 -0.10

0.69 -0.01 -0.02 0.53 0.46 -0.08 0.59 0.28

-0.05 0.43 -0.40 0.23 -0.41 - 0.07 -0.21 0.79

Variance explained (%)

32

18

16

ANOVA model Treatment Day TR x Day

NS *** NS

NS *** NS

*** ***

LSD Treatment MS0 Ml00 M200

-0.19 A 0.15 A 0.05 A

-0.04 A 0.09 A -0.05 A

0.49 A -0.17 B -0.33 B

Sampling date I Aug. 8 Aug. 15Aug. 22 Aug. 29 Aug. 5 Sept. I4 Sept. 27 Sept. 4 Oct. 17 Oct. 24 Oct. 31 Oct.

-0.19 DE -0.63 EF 0.52 BC 0.51 c 0.18 CD -0.90 F 0.08 CD -1.07 F - 1.05 F 1.10 AB 0.52 BC 1.13 A

- 1.08

0.94 A -0.74 E 0.82 A 0.00 BCD 0.04 BC -0.58 DE

H -1.19 H -0.38 FG -0.75 GH 0.29 CDE -0.29 EFG -0.13 EF 0.91 AB 0.53 BCD 1.23 A 0.89 ABC 0.17 DEF

NS

CDE E -0.92 -0.49 CDE 0.99 A 0.19 AB

the end of October (g) photosynthesis level was still high although nitrogen conversion into less active compounds was reduced. Factor 3 accounts for another 16% of the variance. It shows the metabolism rate of the system. The lower the amount of detritus and algae in the water (NORG-W) the lower the respiration in the ponds, which means higher DOMIN and pH levels, and lower amounts of NH4-W. This factor fluctuated

MANURING EFFECTS ON ECOLOGY AND FISH PERFORMANCE

photosynth. 4

.

IN POLYCULTURE

PONDS

129

* MO , _ -=. Ml00 - Mao0

-1

Aug I

I

AWJ 16

hug 29

sep14

cd

4

OCI 24

Fig. 7. Factor analysis of water quality data. Factor 1 (top), Factor 2 (middle) (bottom ) in each treatment during the growing season.

and Factor 3

during the growing season in a similar way in all treatments, and showed significantly lower metabolism in M50 than in the other treatments (Fig. 7). Thus, manuring effect on water quality was also mediated through respiration

A.MILSTEINETAL.

-15

-I

-0.5

0 Factor2

05

I

15

+ nitrogen melabol*sallloa

Fig. 8. Factor analysis of water quality data. Factor 1 vs. Factor 2 in each treatment. Arrows indicate time. Letters are dates: a= l-8 July; b = 15-22 August; c = 29 August; d= 5- 14 September; e = 27 September-4 October; f= 17-24 October; g= 3 1 October.

rate, though this effect ranged third after photosynthesis-decomposition balance and nitrogen metabolization by algae and bacteria, which accounted for 50% of the variability. Sediment analysis The amount of sediments collected in the traps was high and rather variable. This amount seemed to be dependent on the location of each trap within the pond. The rate of sediment accumulation was in the range 200-400 g m-’ day- ‘. These rates are higher by 2 orders of magnitude than either manuring rate (Table 5 ) or primary production (about 4 g C mP2 day-‘, calculated from oxygen profiles). Thus, the main source of the trapped material was indeed resuspension of sediments, and not particles settling down from the water column. Each sediment parameter shows a different pattern of changes related to time and manure loading (treatment). Sulphide (Fig. 9) ranged between 0.2 and I .2 mg g- ‘, with higher concentrations in the higher manure loading, and similar trends in all treatments (low in mid-September, then high till midOctober). Organic carbon concentration in the sediments (Fig. 9) was about 40 mg g- I, increasing somewhat during October; this parameter was also correlated with the manure loading. Ammonium concentration in the sediments (Fig. 10) was about 50 fig/g the first two or three sampling dates, then increasing to near 100 pg g- ’ to decrease to the previous values till the end of the experiment; the ammonium.peak occurred first in the least loaded treatment (M50), and was less pronounced in the most loaded one (M200). Total nitrogen (Fig. 10) fluctuated during August, and then stayed at about 6 mg g-l till the end of th e experiment in M 100 and M200 and at about 4.5 mg g- ’

MANURING EFFECTS ON ECOLOGY AND FISH PERFORMANCE IN POLYCULTURE

Jil

25

Aug

I

Aug

15

Aug

29

Sep 14

Ott

4

Ott

17

act

PONDS

131

31

Fig. 9. Sulphide (top) and organic carbon (bottom) in the sediment in each treatment during the growing season.

in M50. Heterotrophic digestion in the sediments (Fig. 6) decreased from 5-6% at the beginning of the growing season to about 2% at the end; generally the highest heterotrophic digestion occurred in M200 and the lowest in M50. Factor analysis was also run on data of sediment traps (Table 3 ) . The first factor (Factor 1) accounts for 42% of the variance. It shows organic loading and anaerobic conditions, and their negative correlation with heterotrophic activity. This factor showed differences among treatments (M200 > M 100 > M50). It was higher in the second half of the experiment (Fig. 1 1), when temperature dropped and the manure was, possibly, not completely metabolized. The second factor (Factor 2 ) accounts for another

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A. MILSTEIN ET AL.

0

I

6

,

I

I

,

I

I.b-_

? ?4 s

,

m 7 CJ2

0 Jul

I

25

Aug

I

I

Aug

I

15

Aug

29

I

1

Sep 14

act 4

Fig. 10. Ammonium (top) and total nitrogen (bottom) ing the growing season.

1

Ott

17

Ott

31

in the sediment in each treatment dur-

23% of the variance. It reflects microbial action in the sediment (HD-S) to convert available nitrogen (NH,-S) into organic nitrogen (NTOT-S ) . This factor showed the same pattern of differences among treatments as Factor 1, but its values decreased with time (Fig. 11). Treatments Ml00 and M200 showed a similar behaviour in relation to the first two factors through the growing,season, while MS0 was different. These changes are shown in Fig. 12, in which arrows express the time scale and each letter corresponds to one sampling day. Treatments M10’0 and M200 showed higher organic loading and anaerobic conditions (Factor 1) and from September also higher nitrogen metabolization rate (Factor 2) than M50. On the first sediment sampling

MANURING

EFFECTS ON ECOLOGY AND FISH PERFORMANCE IN POLYCULTURE

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TABLE 4 Factor analysis on sediment data, ANOVA of factors and multicomparisons (LSD) between treatments and sampling days (NS = Nonsignificant, **P B> . . n= 72 observations)

NH,-S NTOT-S CORG-S HD-S SH-S Variance explained ANOVA model Treatment Day TR x Day

Factor 1

Factor 2

0.59 0.57 0.88 -0.44 0.69

-0.42 0.64 0.11 0.72 0.15

42

23

*** ***

*** *** **

NS

LSD Treatment M50 Ml00 M200

-0.56 C 0.08 B 0.48 A

-0.58 C 0.12 B 0.46 A

Sampling data 15 Aug. 29 Aug. 14 Sept. 4 Oct. 17 Oct. 3 I Oct.

c -0.54 C -0.63 c -0.54 B 0.29 1.11 A B 0.32

1.30 A -0.10 BC 0.18 B -0.32 CD -0.35 CD -0.70 D

day (b) low organic loading and high nitrogen metabolization rate occurred in all treatments. By the end of August (c) the organic loading on the sediment and the corresponding anaerobic conditions did not change much, while nitrogen transformation decreased in all treatments. In spite of this decrease, metabolism in the sediment was still high enough to avoid accumulation of organic matter. In treatments M 100 and M200 organic loading increased from mid-September onwards (d-f), worsening anaerobic conditions, and nitrogen metabolization decreased. Treatment M50 showed a different pattern, in which microbial activity on nitrogen was lower (d-g), while the loading increase was not so strong as in the other treatments. On the last sampling date (g ) there were no strong changes in M200, but in M 100 and M50 decomposition processes increased.

A. MILSTEIN ET AL.

I

F a C 1 0 r I

0I-

.

-I

heiemir. OCUVllV

nlimgen

2

metob.

,-

0-w

AuQ

,

AUQ 15

AUQ 29

Fig. 11. Factor analysis of sediment ment during the growing season.

F a C t 0 r 1

7

Sep 14

oci

4

Od 17

data. Factor

1 (top)

0.5

I

oci 31

and Factor 2 (bottom)

in each treat-

I 0.5 0 -0.5

hetQret?ophlC acuritr -I 11.5 nitmgonou8

-I matter

docomposition

-0.5

0 Factor2

1.5 *

2

n1tmgen

metaboll~lon

Fig. 12. Factor analysis of sediment data. Factor 1 vs. Factor 2 in each treatment. Arrows indicate time. Letters are dates: b= 15-22 August; c= 29 August; d= 5-14 September; e=27 September-4 October; f= 17-24 October; g= 3 1 October.

M.4NURlNG EFFECTS ON ECOLOGY AND FISH PERFORMANCE IN POLYCULTURE

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DISCUSSION

Organic loading increased in this experiment in two directions, time and treatment. The main sources of variability in the system were related to time. The low effect of treatment was shown in both fish performance and ecological parameters. Manure level affected differently each parameter measured, but in general, when significant differences did occur they were relatively small compared to the change in the amount of manure applied. Tables 1 and 4 show that an increase of 100% or 300% in manure produced an increase of only 12% in total fish yield and of 28% in NORG-W, and a decrease of 2 1% in DOMIN and HD-W and 11% in HD-S. Each doubling of manure input increased CORG-S by 1O%, while SH-S increased by 50% from M50 to M 100 and only by 27% from M 100 to M200. Doubling manure level did not affect common carp growth and yield or NH,-W, but a manure increase of 300% increased these variables in 22% to 26%. No other measured parameter showed significant differences related to manure level. The lack of effect of manure level on the first two water factors points out that the amounts of nutrients and organic matter introduced with the manure in the lower treatment (M50) were at least enough to support algal and bacterial populations in the water, and any extra amounts did not increase autotrophic and heterotrophic activities. Averaged over all the growing period, treatment M50 received 83 kg dry matter ha- ’ day- ‘, 30% of which was carbon and 3.1% nitrogen. This corresponds to a daily dose of 2.5 g C m-’ day-’ and 0.3 g N rnw2 day-’ (Table 5). On the other hand, the sediment factors show that the organic matter introduced in the lower treatment (M50) favoured decomposition processes, while TABLE

4

Multicomparison tests of water and sediment parameters (means different at the 0.05 levels; A > B > C; n = number of observations)

with equal letters are not significantly

Treatment

DOMIN

PH

(mgl-‘) n=

NH,-W

NO,-W (mgl-r)

NORG-W (mgl-‘)

CORG-W

CHLOR

(mgl-‘)

(mgl-I)

(pgl-‘) 168 180 .4 192 A 175 A

M50 Ml00 M200

168 3.7 A 3.1 B 2.8 B

155 8.4 A 8.4 A 8.4 A

167 B 0.23 0.26 AB 0.29 A

167 0.68 A 0.57 A 0.54 A

163 2.21 B 2.81 A 2.85 A

152 78 A 79 A 82 A

Treatment

SH-S

CORG-S

NH4-S

(mgg-‘)

(mgg-‘)

(figg-‘)

NTOT-S (mpg-‘)

HD-S (Iday-‘)

HD-W (% day-‘)

72 0.46 C 0.69 B 0.88 A

83 38 C 42 B 46 A

72 59 A 60 A 62 A

83 4.6 B 5.4 A 5.5 A

167 3.29 B 4.32 B 3.76 A

167 1.05 B 1.20 B 1.42 A

II=

M50 Ml00 M200

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A. MILSTEIN

ET AL.

the higher amounts introduced in the other two treatments enhanced organic synthesis and accumulation (Fig. 12, Table 5 ) . This was reflected in the higher yields of the benthophagic common carp obtained in these treatments. Treatment Ml00 received 165 kg dry matter ha- ’ day- ‘, which represent 5 g C m-* day-’ and 0.5 g N m-* day-‘. This amount of dry matter is 65% higher than that recommended by Olah ( 1986)) but the carbon content is in agreement with that author’s advice. The higher input levels applied in treatment M200, although favouring organic synthesis, resulted in high SH-S levels (0.88 mg g- I ), which may be the reason why M200 did not give a higher carp yield than M 100. Heterotrophic activity is affected by various processes which act independently. Both in water and in sediments heterotrophic activity was negatively correlated with processes which increase organic carbon and nitrogen (first factors). At the same time, for each level of autotrophic activity or organic loading in the sediment, the higher the heterotrophic activity the larger the amount of nitrogen metabolized (second factors). Higher variability occurred in the water body than in the sediment. When all sediment and water variables were analysed together, the resultant factors show the same processes as in the separate analyses. The first common factor was autotrophic-heterotophic balance in the water column, the second was organic loading in sediments, and the third was heterotrophic nitrogen metabolism in sediments. Since effect of treatment was not significant in the first (water) factor, while it was in the sediment ones, manure loading seems to affect the sediment more than the water body. The lack of treatment effect on growth and yield of all fish species, except common carp, is related to this difference in the effect of manure level on water and sediment: while common carp feeds on the bottom (Spataru et al., 1980; Schroeder, 1983), and is more dependent on feed supplied than the other fish present in the pond (Milstein et al., 1988), silver carp feeds on phytoplankton in the water body, and tilapia hybrids also favour natural foods of photosynthetic origin (Spataru, 1982; Schroeder, 1983). It should be noted, however, that fish growth and yields obtained in this experiment were approximately 30% lower than those of previous years (Wohlfarth and Hulata, TABLE 5 Manure input to the ponds, averaged over the whole growing season Treatment

Dry matter (kg ha-’ day-‘)

Carbon (g m2 day-‘)

Nitrogen (g m2 day- ’ )

M50 Ml00 M200

83 165 343

2.5 5.0 10.3

0.3 0.5 1.0

MANURING

EFFECTS ON ECOLOGY AND FISH PERFORMANCE IN POLYCULTURE

PONDS

137

1987 ). Reduced growth rate may have suppressed differences among treatments. For the first time, over a period of 15 years of experimentation on intensive manuring in the same block of ponds, we suffered poor fish performance. In a further experiment conducted in 1989 (to be reported elsewhere) fish growth retardation was even stronger. No change in water or sediment parameters compared to previous years could account for this growth retardation. We may have suffered from delayed effect from using the Arsenal weed killer which was applied in the 1988-1989 seasons, and never before. Elimination of the use of this chemical in 1990, and the normal fish growth rates experienced so far support this conclusion.

REFERENCES Edwards, P., 1980. A review of recycling organic wastes into fish, with emphasis on the tropics. Aquaculture, 2 1: 26 l-279. Kim, J.O. and Mueller, C.W., 1978. Factor analysis. Statistical methods and practical issues. Quantitative Applications in the Social Sciences 14. Sage University, 88 pp. Milstein, A., Hulata, G., and Wohlfarth, G.W., 1988. Canonical correlation analysis of relationships between management inputs and fish growth and yields in polyculture. Aquacult. Fish. Manage., 19: 13-24. Olah, J., 1986. Carp production in manured ponds. In: R. Billard and J. Marcel (Editors), Aquaculture of Cyprinids. INRA, Paris, pp. 295-303. Page, A.L., Miller, R.H. and Keeney, D.R. (Editors), 1982. Methods of Soil Analysis, Part 2, 2nd edition. Am. Sot. Agron. & Soil Sci. Sot. Am. (Publ. ). Raveh. A. and Avnimelech, Y., 1972. Potensiometric determination of soil organic matter. Soil Sci. Sot. Am., Proc., 36 (6): 967. Raveh. A. and Avnimelech, Y., 1979. Total nitrogen analysis in water, soil and plant material with persulphate oxidation. Water Res., 13: 9 1 l-9 12. SAS, 1987. SAS User’s Guide: Statistics, Version 6 Edition. SAS Institute Inc., Cary, NC, 1030 PP. Schroeder, G.L., 1983. Sources of fish and prawn growth in polyculture ponds as indicated by delta-C analysis. Aquaculture, 35: 29-42. Schroeder, G.L., 1987. Carbon pathways in aquatic detrital systems. In: D.J.W. Moriarty and R.S.V. Pullin (Editors), Detritus and Microbial Ecology in Aquaculture. ICLARM Conference Proceedings 14, pp. 2 17-236. Seal, H.L., 1964. Multivariate Statistical Analysis for Biologists. Mathuen, London, 209 pp. Spataru, P., 1982. A contribution to the study ofthe natural food ofSurotherodon hybrids grown under conditions of polyculture, supplementary feed and intensive fertilization. Bamidgeh, 34: 144-l 57. Spataru, P., Hepher, B. and Halevi, A., 1980. The effect of the method of supplementary feed application on the feeding habits of carp (Cyprinus carpio L. ) with regard to natural food in ponds. Hydrobiologia. 72: 17 l-l 78. Standard Methods for the Examination of Water and Wastewater, 1985, 16th Edition. APHAAWWA-WPCF, Washington, DC, 1286 pp. Tang, Y., 1970. Evaluation of balance between fishes and available fish food in multispecies fish culture ponds in Taiwan. Trans., Am. Fish. Sot., 99: 708-7 18. Vollenweider, R.A., 1974. A Manual on Methods for Measuring Primary Production in Aquatic Environments. IBP Handbook 12. Blackwell, Oxford, 225 pp.

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Wohlfarth, G., 1978. Utilization of manure in fish farming. Proc. Fishfarming and Wastes Conf., University College, London. Janssen Services, pp. 78-95. Wohlfarth, G. and Hulata, G., 1987. Use of manures in aquaculture. In: D.J.W. Moriarty and R.S.V. Pullin (Editors), Detritus and Microbial Ecology in Aquaculture. ICLARM Conference Proceedings 14, pp. 353-367. Wohlfarth, G.W. and Schroeder, G.L., 1979. Use of manure in fish farming-a review. Agric. Wastes, 1: 279-299.