Lukowicz 1982 Aquacultural-Engineering

7/28/2019 Lukowicz 1982 Aquacultural-Engineering

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A q u a c u l t u r a l E n g i n e er i n g 1 ( 1 9 8 2 ) 1 2 1 - 1 3 7

I N T E N S I V E C A R P CYPRI NUS CARPI O ( L . ) R E A R I N GIN A F A R M P O N D I N S O U T H E R N G E R M A N Y

A N D IT S E FF E C T S O N W A T E R Q U A L I T Y

M . V . L U K O W I C ZBayerisehe Landesanstalt ffir Fischerei, We ilheimerStrasse 8a, 8130 Starnberg, W est Germ any

A B S T R A C T

E x p e r i m e n t s o v e r t h r e e ye a r s, in a p o n d o f a p p r o x i m a t e l y 1 5 0 0 m 2, t o i n t e n s i fyprod ue t ion a t h igh s to ck ing dens i t i e s w i th con t ro l l ed f e ed in g r e su l t ed i n a subs tan tia li nc rease i n y i e ld (we igh t ga in pe r hec ta re and year : 2 .6 t onn e f o r C3-4 , 9 . 1 t on ne f o rC 2_ 3 , 1 5 . 4 t o n n e f o r C l _ z) . A t t h e s a m e t i m e w a t e r r e q u i r e m e n t c o u ld b e r e d u c e d t o4 m 3 kg -1 f i sh p roduc ed . How ever , t he s t ock ing dens i t i e s ach i eved r e su l t ed i n a con -t i n u o u s ly i n cr e as in g e u t r o p h i ca t i o n e f f e c t w h i c h e x p r e s s e d i t s e l f i n m a s s d e v e l o p m e n to f ph y top lan k ton . Th i s l ed to eons ide rab l e d iu rna l f l uc tua t io ns i n oxy gen concen t ra -t io n ( 0 . 5 - 2 0 . O m g 0 2 l it re -~ ) a n d t o t a l a m m o n i a (O -1 1. O m g N H 3 - N H g litr e- 1,"m a x i m u m o f 1 . 5 m g N H 3 litr e-~ ). T h e h i gh s t o c k i n g d e n s i t y c o n t r i b u t e d i n d ir e c tl y t othe d iu rna l f l nc tua t io ns ( f e r t il i za t i on t h rough faeces and l o s t f e eds ) . How ever , i tscon t r ib u t i on t o t he ove ral l oxyg en dep l e t i on a m ou n ted t o le ss than 25% a t n igh t. Thea m p l i t u d e o f t h e f l u c t u a t i o n w a s m a i n l y d e t e r m i n e d b y t h e p h o t o s y n t h e t i c a n dre sp i ra to ry ac t i v i t y o f t he ph y to p la nk ton and by m ic rob io log ica l degrada tionprocesses . Wi th increas ing wa ter tempe ratu re dur ing sum m er , increas ing feed ing ra te ,con t inu ous f i sh b iomass i nc remen t , and decreas ing li gh t pe r iod pe r day and danger o ft o ta l f i s h s t o c k m o r t a l i t y w a s g r e a te s t i n A u g u s t . O n l y a t m a x i m u m p h o t o s y n t h e t i ca c t i vi t y d u r i n g d a y l i g h t w a s t h e t o t a l a m m o n i a p r o d u c t i o n i n th e p o n d a d e q u a t e lyc o u n t e r a e t e d a n d s u f f i c ie n t o x y g e n p r o d u c e d . E v e n h e a v y a e ra t io n c o u l d n o t a l w a y ssucces s fu l l y p rov ide f o r oxy gen dur ing n igh t. I n o rder t o avo id a b reak dow n o f t hes y s t e m , a lg ae a n d n u t r i en t s h a d t o b e d i l u t e d f r o m t i m e t o t i m e b y e x c e s si v e w a t e rrep lacemen t . De sp i t e t he t emp orary ove r load ing o f t he po nd sy s t em , l os se s in num bersh a d b e e n k e p t b e l o w 6 . 5 % ( n o r m a l l y : 1 0 - 2 0 % ) .

Pe l l e t s were o f f e red v ia s e l f- f e ed ing devices . Fo od up take w as con t inuou s l yr e co r d ed . N o d i u rn a l f e e d i n g r h y t h m i c c o u l d b e o b s e r ve d , b u t f e e d i n g a c t i v i ty w a sen t i r e l y dep en de n t on oxy gen l e ve ls i n po nd wa te r. Fe ed eonver s ion e f fi e i ene i e sreached va lue s be tween 1 .96 and 2 .48 . 1 2 1Aquaeultural Engineering 0 1 4 4 - 8 6 0 9 / 8 2 / 0 0 0 1 - 0 1 2 1 / $ 0 2 . 7 5 A p p l i e d S c i e n c e P ub l i she r s L td ,E n g l a n d , 1 9 8 2P r i n t e d i n G r e a t B r i t a in


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122 M . v . L U C O W I C ZI N T R O D U C T I O N

The a r ea o f a c a rp f a rm ca nno t be i nc r ea sed a rb i t r a r i l y owing to a fr equen t l a ck o fw a t e r o f su f f i ci e n t q u a l it y . A n i n c re a s e i n p r o d u c t i o n m u s t t h e r e f o r e b e b r o u g h t a b o u tby means o f i nc r ea s ing t he y i e ld pe r hec t a r e , i . e . i n t ens i fy ing t he cu l t i va t i on .C o n v e n t i o n a l c a r p f a r m i n g y ie l d s 5 0 0 - 1 5 0 0 k g c ar p p e r y e a r a n d h e c t a r e b a s e d o nn a t u r a l f o o d s u p p l y a n d s u p p l e m e n t a l f ee d i ng . F o r t h e p r o d u c t i o n o f 1 k g fi sh ,2 0 - 3 0 m 3 o f w a t e r a re r e q u i r e d , i n so m e i n s t an c e s c o n s i d e r a b ly m o r e . T h e a p p l i c a ti o no f i n t ens ive me thods o f aquacu l t u r e ( t ank cu l t u r e , wa t e r r e c i r cu l a t i on ) g r ea t l yd e c re a se s t h e w a t e r r e q u i r e m e n t i n c o m p a r i s o n w i t h p o n d c u l t u r e. O n t h e o t h e r h a n d ,t he cos t s f o r ene rgy and compl i ca t ed c l ean ing p rocedu re s a r e cons ide r ab ly h ighe r .

P r e sen t l y t he m a jo r i t y o f s tock ing f i sh and ca rp fo r t he t ab l e a r e g rown in ponds .Pond f a rms a l so t r y t o i n t ens i fy ca rp cu l t i va t i on . T he goa l is t o i nc r ea se t he y i e ld pe rhec t a r e and , a bove a ll , t o r educe t he f i xed cos t s a nd s al a ri e s i n re l a t i onsh ip t o t he ne tp ro f i t . The u sua l supp l emen ta l g r a in s and o the r p l an t f e eds r i ch i n ca rbohydra t e s a ssuch r ep re sen t an i n t ens i f i c a t i on measu re s i nce t he y a l l ow fo r g r ea t e r s t ock dens i t y .B y f u rn i sh i n g c o m p l e t e h i g h - p r o t e in f e ed s w h i c h n o t o n l y s u p p l e m e n t b u t p a r ti a ll yr ep l ace t he na tu r a l f ood supp ly , t he s t ock dens i t y can be fu r t he r i nc r ea sed . Them a x i m u m i n t e n s i ty l e ve l o f p o n d f a r m i n g is re a c h e d o n c e t h e n a t u r a l f o o d s u p p l yp l ays no p r ac t i c a l r o l e and t he f ish on ly f eed o n d ry pe l l e ts .

O n t h i s l ev e l o f p r o d u c t i o n , t h e i m p o r t a n c e o f t h e p o n d i t s e lf f o r th e f is h p o p u l a -t i on ha s changed d r a s t ic a l l y . I t ha s be co m e mere ly a con t a ine r f o r t he ca rp . The y i e ldl imi t is , a t t h i s po in t , no l onge r de t e rm ined by t he f e r ti l i t y o f t he pon d bu t thep h y s i c a l a n d c h e m i c a l q u a l it y o f t h e w a t e r.

I n t ens ive p ro duc t i on pu t s g r ea t s t r a i n on t he na tu r a l pu r i fy ing capac i t y o f t he ca rpp o n d . O n e k i l o g r a m m e o f f is h b u r d e n s t h e w a t e r w i t h a B O D s o f a p p r o x i m a t e l y 3 gp e r d a y . T h e p o n d m u s t h a v e s u f f i c i e n t c a p a c i t y t o b r e a k d o w n t h i s o r g a n i c l o a d .M e t a b o l i c p r o d u c t s m u s t n o t r e a c h a c o n c e n t r a t i o n w h i c h w o u l d h a r m t h e f i s h o rs t u n t t h e i r g r o w t h . T h u s , t h e n a t u r a l c l ea n in g c a p a c i t y b e c o m e s t h e d e t e r m i n i n g f a c t o rf o r s t o c k in g d e n s i t y a n d p r o d u c t i o n y i e ld . I t d e p e n d s o n a v a r i e ty o f fa c t o rs , s o m e o fwh ich can no t no rm a l ly be i n f l uenced - f o r i n s t ance , t he cha r ac t e r o f t he so il , t hewa te r t emp e ra tu r e , t he vege t a t i on , t he l igh t cond i t i ons and t he wa t e r supp ly . S incethe se pa r a m e te r s a r e sub j ec t t o cons t an t changes , the wa t e r qua l i t y in c a rp pond s canshow cons ide r ab l e f l uc tua t i ons .

In t ens ive cu l t i va t i on o f ponds a ims a t op t ima l u t i li z a t i on o f t he ava i l ab l e a r ea andwa te r supp ly and a r e la t ive r edu c t i on o f l abou r , a l l o f w h ich shou ld r e su l t i n m oree c o n o m i c a l c a rp p r o d u c t i o n . I t s h o u l d o f f e r a c o m p r o m i s e b e t w e e n e x t en s i v e p o n dc u l t iv a t i o n a n d m o d e r n s y s t e m s o f a q u a c u l t u r e . T h e p o n d f a r m e r c a n ta k e t h is m i d d l ec o u r s e b y e m p l o y i n g t h e a l re a d y e x i s ti n g p r o d u c t i o n s y s t e m o f th e p o n d w h i lead ju s t ing h i s f a rm ing m e thod s . T he ques t i ons a r e thus r a is ed : wh ich de m ands w i l l havet o b e m e t b y p r o d u c t i o n t e c h n o l o g y a n d w h a t l ev e l o f in t e n s i t y c a n b e s u s ta i n e d b ythe se l f -c leaning capac i ty of the po nd i tsel f? .


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EFFECT OF CARP REARING ON WATER QUALITY 123

MATERIALS AND METHODS

A s t u d y c o n d u c t e d b e t w e e n 1 9 7 2 a n d 1 9 7 4 i n a p o n d o f l o w w a t e r s u p p l y f r o m aw e ll , a t t e m p t e d t o i d e n t i fy p r o b l e m s w h i c h o c c u r i n c o n n e c t i o n w i t h h i g h s t o c k in gd e n s i t y . I n i t ia l l y , t h e p o n d h a d a w a t e r s u r f a c e o f 1 3 5 0 m 2 a n d , a t a n a v e ra g e d e p t h o f6 0 - 6 5 c m , c o n t a i n e d 8 5 0 m 3 o f w a t er . I n 1 9 7 4 , t h e p o n d ' s s u r f a ce w a s e x t e n d e d t o1 4 5 0 m 2 a n d i ts v o l u m e i n c r e a s e d t o 1 2 0 0 m 3 w a t e r b y e x c a v a t i n g m u d t o a d e p t h o f9 0 c m .

A f t e r f i l li n g t h e p o n d a t t h e b e g i n n i n g o f e a c h s e a s o n ( 1 9 7 2 , n o t c a l c u l a t e d ; 1 9 7 3 ,8 5 0 m 3 ; 1 9 7 4 , 1 2 0 0 m 3) w a t e r w a s a d d e d , f o r e v a p o r a t i o n a n d s e e p a g e t h r o u g h o u t t h ep r o d u c t i o n s e a s o n ( 1 9 7 2 , n o t c a l c u l a t e d ; 1 9 7 3 , 3 2 0 m 3 ; 1 9 7 4 , 1 0 5 0 0 m 3 ). A e r a t i o nwi th s im p le d i f f u s e r s ( s ee p o n d p l a n , F ig . 1 ) wa s o n ly n e e d e d a t n ig h t i n 1 9 7 2 . I n1 9 7 3 , a e r a t i o n w a s c o n t i n u o u s t h r o u g h o u t t h e p r o d u c t i o n p e r io d , u si n g t h e d if fu s er s.A d d i t i o n a l a i r l if ts w e r e u s e d i n 1 9 7 4 ( s e e F i g. 1 ) (K n o s c h e , 1 9 7 3 ; v . L u k o w i c z , 1 9 7 4 ) .I n 1 9 7 2 t h e i n s t a l l e d b lo w e r c a p a c i t y wa s 2 5 m 3 h - ] . I n 1 9 7 3 t h i s wa s i n c r e a s e d t o1 2 0 m 3 h - 1 f r o m 2 2 J u n e wh i l e i n 1 9 7 4 t h e i n s t a l l e d c a p a c i t y wa s 9 0 m 3 h - 1 i n i t ia l l y ,r i si n g t o 1 2 0 m 3 h - 1 f r o m 2 8 J u n e .

D u r i n g t h e i n di v i d u al y e a r s o f t h e e x p e r i m e n t , t h e p o n d w a s s t o c k e d w i t h c a r pCyprinus carpio ( L . ) o f v a r y in g a g e s a n d w i th i n c r e a s in g d e n s i t y ( T a b l e 1 ). F e e d w a s

( a ) $ 22 2 m

x x x x x x $ 30 " 9 x o x 0 . 8 x x 0 . 7 x 0 " 6 - - 0 " 5 0 "4 d e pth

c , 6 9 m i n le t

II + + + x _ _ x _ o 22m

l i m [ 170 Os ./' - f i g + 0 .9 0 .8 - depth

I 7 5 mi n l e tF ig . 1 . P lan o f po nd . (a ) 19 72/1973, 135 0 m~; (b ) 197 4, 1480 mL $1, $2 , $3 , $4 : sampl ing

points 1-4. X, Simple diffusers; +, air lifts; o, demand feeder.


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124 M.v. LUKOWICZ

administered as pellets, of a crude protein content of 32-35% by weight. It wasoffered by dem and feeders where the carp could feed according to their needs.

To register the feeding times, the demand feeder was equipped with a device, thecons truc tion of which is illustrated in Fig. 2. The pen dul um (1) extendi ng from a droppipe (2) into the water (3) is covered in one place by a cuff of zinc-platted sheet iron(4). Cuff and pe ndu lum are separated by water proof i nsula tion material. A contac tring (5) around the cuff is connected to the demand feeder by a metal strip (6). Thisring is also made of stainless zinc-plated sheet iron. Two wires (7) connect cuf f andcontact ring to a magnetograph (8) which transfers impulses from the swingingpendulum to a paper scroll (9). A cone-shaped screen (10) which is attached to thepen dul um prevents dry feed from falling betwe en the cont acts and staying there. Thepellets which glance off the inner screen are directed back by an outer screen (11).Thus the food pellets do not disperse widely but fall into the water close to thependulum. In addition, the larger outer screen protects the contact device against rain.

TABLE 1Production data of the intensive pond farming of carps in 1972, 1973 and 1974Year 1972 1973 1974Pond area, m 2 1 350 1 350 1 480Experimental time, days 65 161 171S t o c k i n g C 3 C 2 C 1number 400 1 350 7 500individual weight, g 908 211 35.9total weight, kg 363.0 285.0 269-0total weight, kg ha -1 2 688.9 2 111.1 1 817.6Y i e l d C 4 C 3 C 2

number 398 1 305 7 020individual weight, g 1 353 1 157 362.9total weight, kg 538.5 1 510.0 2 547.8total weight, kg ha -1 3 988-9 11 185.2 17 214.9L o s s e snumber 2 45 480per cent 0.5 3.3 6.4Weigh t gain

individual, g 445 946 327total, kg 175.5 1 225.0 2 278.8total, kgha-; 1 300.0 9074.1 15 397.3F e e d i n g

amount, kg 375.0 3 042.0 4 472.5feed conversion (kg feed kg -~ weight gain) 2.14 2.48 1.96


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E F F E C T O F C A R P R E A R I N G O N W A T E R Q U A L I T Y 125

1 m 2 D

1 1 - - ~ ~ 9F ig . 2 . C o n t a c t c o n s t r u c t i o n o n t h e d e m a n d f e e d e r a n d d e v ic e f o r r e g is t r a ti o n o f t h e f e e d in gt i m e s ( f o r e x p l a n a t i o n s s e e t e x t )

The construct ion was adjusted such that contact was only established when fish movedthe pendulum and not waves.

Finally regular monitoring of the condition of the water (temperature, tonnes, pH,O2, NH3-NH4 ACC) gave a reliable picture of the pond. Water samples (two replicates)were drawn daily, except on weekends, at 8.00 a.m. and 4.00 p.m. near the surfaceand at the bottom. Additional samples taken on certain days shortly before sunrisesupplemented the routine measurements. On a number of days, the measuring of watervalues, air temperature and light intensity extended over a period of 32 h at 2-hintervals.

R E S U L T S A N D D I SC U S S I O N

Water qua li tyThe water quality of the experimental pond fluctuated according to a daily rhythm.

The oxygen content was most affected. While a maximum fish quantity of a little lessthan 4000 kg ha -~ during 1972 created no dangerous deterioration o f water quality,an increase in stocking density in 1973 and 1974 posed serious problems. Figure 3shows the water values (temperature, pH, 02) for one week in May, June and Octoberof 1973. As expected, fluctuations according to the time of day could be observed.The values measured in the afternoon were always higher than in the morning. Dailyfluctuations were relatively small during May. The variations in oxygen content didnot exceed 4 mg litre -1. During the month of June, the oxygen values increased from5 to 6 mg litre -x measured in the morning to 20 mg litre -1 during the day which isequal to an oxygen saturation of 235%. Similarly, the pH value was less stable in Junethan in May. The differences in pH and 02 values were a result of the assimilation of


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1 2 6 M . v , L U K O W l C Z

L ~ .

~ ~ ~a D ~

~ ' ~ 0

4~


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EFFECT OF CARP REARING ON WATER QUALITY 127phy top l ank ton wh ich had deve loped i n to a dense a lgae cu l t u r e i n June l end ing ano p a q u e g r e e n c o l o u ri n g t o t h e p o n d u n t i l a u t u m n . T h e r e f o r e , t h e p H a n d O 2 c u r ve s o fOc tobe r r e sem bled t hose o f June . Ove ra ll , t he f l uc tua t i ons i n pH leve ls r ema inedwi th in l im i ts . The va lue s d id no t d rop be low pH 8 -0 , ye t a lso neve r exceed ed pH 9 -0 .T h is w a s d u e t o t h e g o o d b u f f e r i n g o f t h e w a t e r ; i ts c al c i u m b ic a r b o n a t e c o n t e n t o n l yd r o p p e d b e l o w a n A C C ( a c i d c o m b i n i n g c a p a c i t y ) o f 5 . 0 a t t h e b e g i n n i n g a n d a t t h eend o f t he s ea son .

E v a l u a t i o n o f s a m p l e s ta k e n a t 8 . 0 0 a. m . d o e s n o t r e f le c t t h e d e v e l o p m e n t o f t h eoxy gen r eg ime du r ing t he n igh t. F igu re 4 shows the d i f fe r ences i n oxy gen con t en t s o fthe w a te r a t dawn ( co lum n 1 , ha t ch ed ) and a t 8 . 00 a .m . ( co lum n 3 , ha t ched ) . Dur ingJune , wh en n igh t s a r e sho r t e s t , t he oxy gen c on t en t i nc r ea sed by 7 mg li t re -1 be tw een4 . 0 0 a .m . a n d 8 . 0 0 a .m . O n 2 2 J u n e 1 9 7 3 t h e n i g h t v al ue s t a k e n a t a m a x i m u m d i s ta n c ef rom the d i f fu se r d ro ppe d t o 0 .6 m g O2 li t re -1 ( i.e . a s a tu r a t i on o f 6%) . Thus , a l a rge rb low er was i n s t a ll ed . I n Sep t em ber , t he d i f f e r ences we re le s s p ron oun ced a s t heoxygen con t en t r ema ined a t a h ighe r l eve l du r ing t he n igh t and t he t ime span fo ra s s imi l a ti on o f the p l ank ton a lgae was sho r t e r b e twee n t he ea r ly morn ing mea su re -m e n t s ( 5 .0 0 a .m . - 5 . 3 0 a . m . ) a n d t h e r o u t i n e m e a s u r e m e n t s ( 8 .0 0 a .m . ) . T h e m i d d l e ,b l an k co lu m ns i n F ig . 4 r ep re sen t t he ox ygen con t en t s nea r t he d i f fu se r a t dawn .

m g 0 2 / I8

7

6 , ~ ~

,,

v vA ~. \

\ % VA V,

2 2 . 6 . 2 9 . 6 . 3 0 . 6 . 2 0 7 . 3 . 8 . 1 . 9 . 3 . 9 . 6 . 9 . 7 . 9 . 2 2 . 9 .D a t eFig. 4. Oxyge n conten t in different places of the pon d and at different times of day in 1973.Colum n 1 (hatched): measurements taken at dawn away from diffuser (sampling point 2). Column2 (blank): measurements taken at dawn near diffuser (sampling point 3). Column 3 (hatched)"

meas ureme nts taken at 8.00 a.m. - mean values.


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128 M . v . L U K O W I C ZFigu re 5 ou t l i ne s t he da i l y rhy thm o f wa te r va lues du r ing 32 h . These cu rves c l ea r ly

i l l u s tr a t e t he d i r ec t r e l a t i onsh ip o f oxy gen con t e n t and pH va lue t o l igh t in t ens i t yw i t h a lo g ic a l s h i f t o f m a x i m u m a n d m i n i m u m v a lu e s. T h e h i g h e r o x y g e n c o n t e n t a tt he wa te r su r f ace du r ing t he day was a l so co r r e l a t ed t o l i gh t i n t ens i t y . Dur ing t hen i g h t, t h e a v e ra g e v al ue s m e a s u r e d a t t h e b o t t o m a n d th e s u r f a ce o f t h e p o n d w e r ea p p r o x i m a t e l y t h e s a m e .

T h e c o r r e l a ti o n s d i s cu s se d c l e a r ly s h o w t h a t t h e p h y t o p l a n k t o n w a s m a i n l yr e s p o n si b le f o r t h e f l u c t u a ti o n s i n o x y g e n c o n t e n t s i n t h e e x p e r i m e n t a l p o n d . I ncom par i son , t he o xyg en dep l e t i on due t o t he f i sh du r ing t he n igh t was r e l a ti ve lys m a ll . T h i s c a n b e d o c u m e n t e d b y c a l cu l a ti n g t h e o x y g e n b a la n c e . A t th e e n d o f J u l y ,t h e o x y g e n c o n t e n t f r e q u e n tl y d ro p p e d b y 1 8 m g l i t r e -1 w i t h in 1 2 h ( 2 . 0 0 p . m . -2 .00 a .m . ) . Th i s equa l s a t o t a l dec rea se o f 15 .3 kg 02 i n t he pond a t a wa t e r vo lume o f8 5 0 m 31 T h e o x y g e n r e q u i r e m e n t o f t h e f is h w a s d e t e r m i n e d b y t h e m e t a b o l i ci n t e n s i t y w h i c h i n t u r n d e p e n d e d o n f o o d i n t a k e a n d w a t e r t e m p e r a t u r e . C o n si d e ri n gthe s iz e o f t he ex pe r im en ta l c a rps and t he r edu ced f eed ing ac t i v i t y du r ing t he n igh t , anh o u r l y c o n s u m p t i o n o f 3 0 0 m g 0 2 k g -1 f i s h c a n b e u s e d a s a b a s is o f c a l cu l a ti o n . T h et o t a l f is h s t o c k , w h i c h a t th e a b o v e m e n t i o n e d t i m e w e i g h ed 1 0 0 0 k g , t h u s t o o k u pon ly 3 .6 kg 02 fo r r e sp i r a t i on . Th i s c a l cu l a t i on does no t t ake i n to accoun t t he amoun to f o x y g e n a d d e d t h r o u g h a e r a t io n a n d n a t u r a l g a s e x c h a n g e a t t h e w a t e r s u r f a c e; t h iso x y g e n m u s t a l s o h a v e b e e n u s e d u p b y t h e p l a n k t o n a l g a e a n d t h e m u d ( T o i e t a l . ,1 9 6 0 ). T h e p o s s i b i li t y o f o x y g e n d e p l e t i o n t h r o u g h l o s s o f f e e d c a n b e e x c l u d e d o w i n gt o t h e u s e o f d e m a n d f e ed e r s.

T h e h i g h s t o c k in g d e n s i t y w a s t h e re f o r e n o t d i r e c t ly c o n n e c t e d t o th e o x y g e nreg ime o f t he wa te r . I t was , how eve r , r e l a t ed t o t he b io log i ca l and eco log i ca l con -d i ti o n s i n t h e p o n d . H i g h s t o c k in g d e n s i t y u n d o u b t e d l y c o n t r i b u t e d d e c is iv e ly to th ef e r t i l iz a t i on o f t he pon d . Th i s c aused t he h igh leve l o f eu t rop h i ca t i o n i n t he expe r i-m e n t a l p o n d a n d t h e e x c e s si v e d e v e l o p m e n t o f th e p h y t o p l a n k t o n . T h e s u b s e q u e n tm e c h a n i s m o f o x y g e n s u p e r s a t u r a t io n a n d d e p l e t io n t o o k i t s c o u r se , to a la rg e e x t e n t ,i ndep ende n t o f t he f i sh . The i n f luence o f a e r a t i on on t he oxyge n con t en t i s show n inF ig . 6 ; Dur ing a s e r ie s o f m easu rem en t s l a s ti ng 32 h , O2 va lue s nea r t he d i f fu se rs we reh ighe r t han va lue s measu red i n p l ace s away f rom the d i f fu se r s . Espec i a l l y du r ing t hec r i t i c a l t i m e b e t w e e n 2 . 0 0 a . m . a n d 6 . 0 0 a . m . a e r a t i o n i m p r o v e d t h e o x y g e n c o n t e n tb y a p p r o x i m a t e l y 1 m g l it re -1 .

F u r t h e r m o r e , a e r a t io n p r o v i d e d a m i x i n g o f th e w a t e r w i th i n t h e p o n d . F i g u re 7s h o w s t h e d i f fe r e n c e b e t w e e n b o t t o m a n d s u r f a c e v a lu e s o f o x y g e n d e p en d i n g o n t h ed i s t ance t o t he d i f fu se r s . I n non -ae ra t ed p l ace s , t he su r f ace wa te r con t a ined up t o5 .7 mg 02 l i t r e -1 mo re t h an t he bo t t o m w a te r du r ing the day . Th i s ve r t ic a l d rop i n 02c o n t e n t d e v e l o p e d b e t w e e n t h e t o p w a t e r la y e r w i th m a x i m u m o x y g e n i n t a k e ( a ir ,a s s im i l a ti o n ) a n d t h e b o t t o m w a t e r l a y e r w i th m a x i m u m 0 2 d e p l e t i o n a n d t h e l o w e s ta s s imi l a ti on r a t e , even t ho ugh th e po nd w as on ly 40 cm deep i n t he p l ace s whe rem easu rem en t s we re t aken . Dur ing t he n igh t , t he se d i f fe r ences d i s appea red owing t othe absence o f sun l igh t . Nea r t he d i f fu se rs , how eve r , t he d eepe r l aye r s o f wa t e r


9/17


Tih leo f 10 12 14 16 18 20 22 24 2 4 6 8 10 12 14 16, , ~D a y ' ' A i r20 / / ~ e m p e r a t u r e in C / 20

10 10W a t e r222321 ~ t e m p e r a t u r e ~ J - n C / / 2321

20 20Light8C tenslt~ n 000/ 80

60 604 0 , 4 0

2 0 2 0

o

8 8

14 ~ O x y g e n c o n t e n t m g O 2 / 1 / / _ _ _ ~ 1 4, , / . . . - ,% - - ~ u r ~ a e e / / 1 , ,/ l" ",,~ -- -- Bottom // I,o / , - \ / .10, / , . ' ' \ / , , , ,

4 ~ / 4

2 2

0 0T i m e s o f feed ing

i ! t i il a o I 1 2 I t 4 1 6 1 8 2 1 0 2 2 2 1 4 2 4 6 8 I t 0 1 1 2 I 1 4 1 62 . 8 . 1 9 7 3 3 . 8 . 1 9 7 3Fig. 5. Water values, light intensity, and feeding activity during 32 h in August 1973 (samplingpoint 1).


10/17

130 M . v . L U K O W I C ZT i m eo fd a y 0 10 12 14 16 10 20 22 24 2 4 6 8 19 12 14 16 h

1 8 4 82 m f r o m d i f f u s e rI G/ / / \ k . . . . . m a x . d i s t a n c e f r o m d i f f u s e r

101214 / / ~ \ ' \\ ,\ ~ 1 2 // / /7 1014

/ "~ /J8 / \ . . / / / 0/ \~ / /

~ _ _ _ / 2m g 0 2 / I 0 : , , , , o1 '0 1'2 1'4 1'6 1 ' 8 2 ' 0 2'2 2'4 2 4 6 8 1 ; l i 14 IE1 9 . 7 .1 9 7 3 2 0 . 7 . 1 9 7 3

F ig . 6 . Ox yge n c on te n t i n d i f f e r e n t d i s ta nc e s f r om d i f fu se r (s a m pling po in t s 2 a nd 3 ) .

T i m eo fa a y 10 12 t4 1G 18 2,0 22 24 2 4 6 8 10 12 14 16 h^

5 / ~ 52 m f r o m d i f f u s e r/4 " ~ . . . . . m a x . d i s t a n c e f r o m d i f f u s e r 4/3 i ~ 3

/\ / "

rag. 02/1 o ~" ~ ~ ~ . . . . . .1 0 I | 2 1 1 4 1 ' 6 1 . 8 2~) " 212 2'4 2 ; 6 ; I ; I I 1 1 1 61 9 . 7 .1 9 7 3 2 0 . 7 . 1 9 7 3

F ig . 7 . D i f fe r e n ce s b e t w e e n o x y g e n c o n t e n t s a t p o n d s u r f a c e a n d p o n d b o t t o m b o t h a t 2 m a n dm a x im um d i s t a nc e f r om d i f f u se r ( s a m pl ing po in t 3 ) .


11/17

EFFECT OF CARP REARING ON WATER QUALITY 131contained only 1 mg litre -1 less oxygen than the surface water. In some cases, thewater of the surface contained even less oxygen, which is reflected in Fig. 7 by pointsof the curve below zero.

In spite of continuous aeration, the oxygen conditions in the experimental pondwere fairly critical. Not even aeration could always balance the oxygen depletionduring night time. It was nevertheless useful, as shown in Fig. 4 and Fig. 6. Thebehaviour of the fish proves this as well, since they always gathered around thediffusers for emergency breathing. An incident which was critical for the fish stockoccurred on 7 August 1973. The air temperature had suddenly droplaed to 18-5Cfrom 32C on the previous day. The plankton algae began to die, and the wateracquired a black colouring. At 8.00 a.m. the oxygen values ranged between 0.6 and1.1 mg litre -1. Even at a noon value of 2 mg litre -1, the carps had not yet s toppedemergency breathing. To save the fish stock, it was necessary to pump well water intothe pond at approximately 20 litre s -1 and 12C. Within 21 h, the pond water hadbeen exchanged almost twice. The purpose of this measure was not so much a directsupply of oxygen; the well water itself only contained 3.7 mg 02 litre -1 but the waterflow was meant to flush out a large portion of the decomposing algae and to dilutethe luxurious phytoplankton culture. During this procedure, the water temperaturedropped to 15C and rose only during the next two days to 20C. By 8 August 1973,the oxygen content had recovered at 8 mg litre -~. Reproduction o f phytop lanktonresumed, and within a few days, the pond had reverted to its former condition. Asa security measure, small amounts of fresh water were added periodically duringAugust and September as a top-up as well as for flushing through water.The presence of ammonia created few problems in 1972 and 1973. Rarely andinsignificantly did the total ammonia contents of the water rise above 0.2 mg litre -1.As a rule, it remained between 0.1 and 0-15 mg litre -1. There was no threat to the fishfrom that side. However, in 1974, as of June the development of ammonia becamealarming. In some instances, 11 mg litre -1 of total ammonia were measured. At a watertemperature of 21C and a pH value of 8.5, this meant approximately 1.5 mg litre -1of unionized ammonia. There was, in fact, no acute fish mortality. Yet, the inferiorwater quality had a negative influence on the growth of fish and the losses.

Ammonia is consumed by micro-organisms and algae. The speed of NH3-NH4degradation is linked to the metabolism of the consuming organisms which, in turn,depends on external factors like temperature and light. Figure 8 shows the develop-ment of water values in July 1974 as an example for the influence of the weather onthe assimilation by the plank ton and the degradation of the total ammonia. The curveoutlines the values measured in the afternoon, i.e. at the end of the daily assimilationperiod. The weather conditions are roughly characterised by the letters S (sunny),C (changing), O (overcast). Parameters for the assimilation activity of phytop lanktonare pH value, 02 content and, in contrast to these, the ACC. During the beginning andmiddle of July, the bad weather was only interrupted by a few sunny days. Therelatively low daily maximum values of pH (under 8.5) and oxygen (under 9.0 mg


12/17

132 M.v. LUKOWICZJu l y

D a t e 2 4 6 8 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8 3 0I I I I I I ! I I I I I | I | I I I | I I I I I I I I I I l I

W e a t h e r o s c c o s o o o c s o o o c s s o s s s s s s2 ,2 2 W a t e r t e m p e r a t u r e C . I

I9 l i / N ~ - I -

8

A C C - A c i d c o m b i n i n g c a p a c i t y41 6 ~ - - - - - ~12 Oxygen c o n t e n t m g 02 / I

!w = !8 . I I ": 1 I

'1 I

4

0 S C C 0 S 0 0 0 C S 0 0 0 C S S 0 S S S S S S

Fig. 8. D ai ly water values at 4.00 p.m. in July 1974: S, sunny; C, changing; O, overcast (samplingpoint 4).

l i tr e - 1 ) a s muc h a s t he h igh ACC (a lm os t 6 ) we re s i gns o f a l ow a s s imi l a ti on r a t e .Dur ing t h i s t ime , t he N H3-NH 4 va lue s we re ve ry h igh and cou ld o n ly be r educed byadd ing wa te r on 10 J u ly (176 m3) , 13 Ju ly (39 2 m 3 ) and 23 Ju ly (347 m 3 ) ( ( . . . . . ) ,F ig . 8 ) . No t even t he add i t i on o f 37 .5 kg g roun d qu i ck l ime (25 0 kg ha -1, 85% CaO)o n 1 7 J u l y s e e m e d t o b r i n g a b o u t a s ig n i fi c an t d ec r e as e o f t h e t o t a l a m m o n i a le v el( ( . . . . ) , F ig . 8 ) . T h e a p p l i c a ti o n o f li m e ( 2 4 J u n e , l 0 J u l y a n d 1 7 J u l y ) w a s i n t e n d e dt o s p e e d u p t h e c o n v e r s i o n o f m e t a b o l i c p r o d u c t s . I t w a s d is c o n t in u e d , h o w e v e r , a f t e rt h e t h i rd a t t e m p t t o a v o i d t h e d a n g e r t h a t h i g h p H v a lu e s h a v e o n t h e N H a - N I J ~ba l ance .T h e p e r i o d o f s u n n y w e a t h e r a t t h e e n d o f J u n e h a d a f a v o u r a b le e f f e c t o n th ep l an k to n a s s imi l a ti on . T h i s m an i f e s t ed i ts e l f i n i nc r ea sing pH va lue s (up t o 9 .2 ) and 02


13/17

E F F E C T O F C A R P R E A R I N G O N W A T E R Q U A L I T Y 133con t en t s ( up t o 16 m g l i t re - ~) and t he con s um pt i on o f c a l c i um b i ca r bon a t e di ss o lvedi n t he w a t e r. T he ACC d r op ped t o va lue s a r ound 4 . At t he sam e t i m e , the t o t a la m m o n i a c o n t e n t d e c r e as e d t o s u c h a n e x t e n t t h a t o n l y h a rm l e ss a m o u n t s o f t o t a lam m oni a ( be l ow 1 m g l i tr e - ~) cou l d be de t e c t ed i n t he wa t e r .

The p ond ' s r e ac t i on t o t h e we a t he r con d i t i ons c l ea rl y dem ons t r a t e s t he con f l ic t i ngs ign i fi c ance o f excess ive p r od uc t i o n o f phy t op l ank t on f o r wa t e r qua l i t y . On the on ehand , t he p l an k t on a lgae caus e an i n s t ab i li t y i n oxyg en cond i t i ons t h r ou gh dange r ousdep l e t i on ac t i v i t y du r ing t he n i gh t. O n t he o t he r hand , t hey ca r r y t he im por t an tf unc t i on o f p r odu c i ng 02 du r i ng the d ay and o f e l im i na t ing m e t abo l i c p r oduc t s . Thep h y t o p l a n k t o n o f t h e p o n d c o n s is te d m a i n l y o f gr e e n alg ae o f t h e o r d e r Chlorococcales(scenedesmus, actinastrum, ancistrodesmus an d pediastrum).

A n i m p o r t a n t , y e t o f t e n n e g l ec t e d p a r a m e t e r o f p r o d u c t i o n i s t h e r e q u i r e d q u a n t i t yo f wa t e r w h i ch ha s becom e even m or e s ca rce as a na t u r a l re s ou r ce . Th i s r equ i r em en twas com pu t ed on t he ba s i s o f quan t i t i e s needed f o r f i l l i ng t he expe r i m en t a l pond i nt he s p r ing , f o r com pens a t i ng l o ss b y evapo r a t i on and f o r wa t e r s upp l y in em er genc ie s .The wa t e r vo l um e o f t he ex pe r i m e n t a l pon d was yea r l y r ep l aced 5 - 8 ti m es . At a t o t a lcon s um pt i on t he r e f o r e o f 4 - 4 . 5 m 3 wa t e r pe r 1 kg in we i gh t gain o f f is h ( t he wa t e rquo t i en t , WQ) t h i s c om par e s ve r y f avour ab l y wi t h con ven t i ona l pon d f a r m i ng , i. e. awa t e r quo t i en t o f 20 - 30 m 3 kg -1 ga i ned .

The c ons t an t l y chang i ng wa t e r cond i t i ons w i t h r epea t ed em er genc y s i tua t i onsplaced the f i sh un der ph ys io logica l s tress. In addi t ion , h igh s tocking d ens i ty fos te re dt he r ap i d s p r ead o f pa ra s it e s and pa t ho l og i ca l agen ts . Ho weve r , t h r ou gh ou t t he yea r so f t he expe r i m en t , t he lo ss es r em a i ned wi t h i n accep t ab l e l im i t s at 0 . 5 - 6 . 4 % . Loss eswer e obs e r ved e s pec ia l ly when wa t e r s upp l y was l im i t ed ( l ow W Q) , even in t he abs enceo f a n i m m e d i a t e e m e r g e n c y .Feed in take

Bas ed on t he h i gh s t ock i ng dens i t y , i t c an be a s s um ed t ha t t h e ca r ps on l y f ed on t heapp l i ed d r y pe l le t s. E xam i na t i ons o f t he pon d a t r egu l a r in t e rva l s con f i r m ed th i sa s s um pt i on ; hence t he r e w e r e ha r d l y any f oo d o rgan i sm s available ( v . Luk owi cz ,1973) .

Und e r t he de s c r i bed expe r i m en t a l cond i t i ons , f e ed i ng f r om t he dem and f eede r wasp r ac t i c a ll y i den t i ca l wi t h f oo d in t ake a s s uch. Th e ca rp s t ock o f 1972 d i d no t m a i n t a ins e t f e ed i ng t im es and paus es . I n t he cou r s e o f the e xpe r i m en t , t he f is h fed a t al l hou r so f d a y a n d n i g h t ( v. L u k o w i c z , 19 7 2 ) . H a y i n g w i th t h e p e n d u l u m w i t h o u t f e e d i n ta k ecan be exc l uded . A p l a s ti c bowl o f 1 m i n d i am e t e r p l aced und e r nea t h the dem andf eede r neve r con t a i ned f eed r em n an t s . U s ua l ly t he ca r p had a l r eady s napped up t he f eeda t t he w a t e r s u r f ace . Of t en t h ey s t uck t he i r heads ou t o f t he wa t e r t o i m m ed i a t e l yca tc h th e fa l ling pe l l e ts .

Owi ng t o s u f f i c i en t wa t e r qua l i t y in 1972 , t he ca r ps f ed du r ing day and n i gh t . I ncon t r a s t t o t h i s, f e ed in t ake was s ub j ec t t o a d i u r na l r hy t hm i n 1973 depen d i ng on t het i m e o f day . Dur i ng t he n i gh t , f e ed ing ac t i v i ty was g r ea t ly l i m i ted . Th e de t e r m i n i ng


14/17

134 M.v. LUKOWICZ

Time o f day0 2 4 6 8 10 12 14 16 18 20 22 24 h

s / 1 ~ , , , , , . . . . March/Apr i l 31 lO0 '-~ J r ~ ~ _....~ 0

15 15l o June 26 l o

5 5o o

2o15 ~ 1510 Ju ly 25 !o5 5o o

2o Augu st 20 zo15 ~ - ~ 1510 10s ~ 50 0

20 20i s - - ~ - 1510 105 September 22 so 0

Num berof lo Octobe r 7 lodays s ~ ~ ~ . s

0 I I I I I / / I I ~ " " - | / 02 4 6 8 10 12 14 16 18 20 22 24

Fig. 9. Distribut ion of days when feeding took place at set hours in March/April through October1973. (Registered days of a month .)


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EFFECT OF CARP REARING ON WATER QUALITY 135f ac t o r was , above a ll, t he chang ing o xyge n co n t en t . F i gu r e 9 ou tl i ne s t he r eco r d i ng o ff eed i ng ac t iv i t y a t f i xed hour s o f t he day by i nd iv i dua l m o n t hs . The nu m b er beh i ndt he nam e o f t he m on t h s igni fie s t he num ber o f days u s ed f o r eva l ua t ion . The r em a i n -i ng days we r e s k i pped becaus e e i t he r no f eed i ng ac t i v i t y occu r r ed o r t e chn i ca lp r ob l em s p r even t ed t he r eco r d ing . Th e i nd i v idua l po i n t s i n the cu r ves we r e com pu t edby add i ng a ll days on w h i ch f eed i ng t ook p l ace a t t he f u l l hou r s .

Feed i ng ac t i v i ty o f t he expe r i m en t a l c a r p was m a i n l y day t i m e o r i en t ed . Dur ing thenight , be tw een 2 .00 a .m. a nd 4 .00 a .m. , the f ish fed the l eas t. T he curves in Fig . 9f o r M ar ch t h r oug h M ay and f o r Sep t em b er t h r ou gh Oc t obe r r un f a i rl y fi a t; ye t evenhe r e , i nc r ea s ed day t i m e ac t i v i t y i s no t i c eab l e . Th i s c an pa r t i a l l y be a t t r i bu t ed t o t hel ow n i gh t t i m e t em p e r a t u r e s s i nce cas es o f a la ck o f oxy gen o ccu r r ed i n f r eque n t l ydur ing tha t per iod . Th e grea tes t n ight t ime s lacks in feeding ac t iv i ty were regi s te redi n J une , J u l y and Augus t . Th i s was c l ea rl y caus ed by t he ch r on i c l a ck o f oxyg endur ing the n ight s o f these mo nths . O nly a few night t ime feedings to ok p lace inAugus t , whe r ea s t he f i s h con t i nuou s l y f ed du r ing t he day t i m e . Th us , t he cu r ves s how ad i s t inc t p l a t eau ove r the expe r i m en t a l pe r i od . Th is p la t eau ex t end s be t w een 9 . 00 a . m .and 5 . 00 p . m . du r i ng J u ne wh i ch t hen f o ll ows a g r adua l dec l ine in t o t he n i gh t. Th i sdec l ine i s r e l a ted t o wa t e r t em p e r a t u r e s o f ove r 15C du r i ng m an y n i gh t s i n June . Th ecu r ve dec li ne s ve r y s ha r p l y f r om 12 . 00 m i dn i gh t t o 2 . 00 a . m . Th i s is a re s u l t o f oxygendeple t ion . The gradual inc l ine to the p la teau i s once aga in t empera ture re la ted s inceoxyg en co nd i t i ons du r i ng t he l ong days i n J une ( F i g . 4 ) wou l d no r m a l l y have i n i t ia t edan ea r l y s t a r t o f t he phas e o f m ax i m um f eed i ng ac t i v it y . The p l a t eau f o r J u l y isobv i ous l y l onge r ( 6 . 00 a . m . - 7 . 00 a . m . ) wi t h a s har p cu r ve i nc li ne and dec l i ne be f o r eand a f t e r i t . Th e n i gh t s we r e w a r m s o t ha t f e ed ing was on l y in f l uenced by t he oxyg encon t en t . Th i s als o app l i ed ba s i ca l ly t o Augus t . The m o s t s ha r p l y con t ou r ed p la t eau isle ss e x t en ded becaus e n i gh t s we r e becom i ng l onge r i n Augus t , no t i c eab l y s ho r t en ingt he a s s im i l a ti on t im e . On l y in S ep t em ber d i d n igh t f eed i ng beco m e m o r e f r equen tonc e again. Th e p la teau in the ac t iv i ty curve s ti ll r em ains ; i t is , how ever , une ven lydeve l oped and g r adua ll y t he cu r ve leve ls o f f . I n Sep t em ber , low o xyg en leve ls we r eno l onge r t he de t e r m i n i ng l i m i t a t i on f ac t o r f o r t he ca r ps ' appe t i t e s . Tem per a t u r ega ined increas ing impo r tanc e unt i l O ctob er . Th e d iagram in Fig . 9 c lear ly shows thet r ans i t ion i n t he e f f ec t s o f t em pe r a t u r e and oxy gen on t he f eed i ng behav i ou r o f t hef ish . Thi s pa t t e r n was repe a ted in 1974, i .e . the f i sh adjus ted the i r f eeding ac t iv i ty tot he chang ing wa t e r qua l i t y .Results of production and economyThe f igu r e s f o r t he f is h p r odu c t i on du r i ng t he i nd i v idua l yea r s a re s how n i n Tab l e 1 .The t o t a l i nc rea s e was g r ea t e r t he l ower t he i nd iv i dua l we i gh t o f t he s t ocked ca rps .I n t ens i ve cu l t i va t ion du r i ng 1972 was app l i ed f o r on l y ha l f t he p r o du c t i on pe r i od( 17 J u l y - 15 Sep t em ber ) . I nd i v idua l we i gh t i nc r em en t a s m u ch as f eed conve r s i onr em a i ned wi t h i n t h e r ange o f t he u s ua l p r od uc t i o n expec t a t i ons f o r t he i nd i v idua l ageg r oups .


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136 M . v . L U K O W I C ZTo judge t he f ea s ib i li t y o f p rodu c t i on p roced u re s f o r p r ac t i c a l f a rming , i t is

neces sa ry t o exam ine i t s p ro f i t ab i l i t y . T he i n t ens ive cu l t u r e i n 1972 can on ly bev i ewed a s a p r e - exp e r im en t w h ich was no t eva lua t ed fo r p ro f i t . C3 p ro du c t i on t h roug h1 9 7 3 w a s n o t e c o n o m i c a l b e c a u s e o f e x p e n d i t u r e o n s t o c k i n g f i sh ; fe e d a n d e l e c tr i c it ya lone l ay a bove t he ne t ga in . I n co n t r a s t t o t h i s , C2 p ro du c t i o n t h ro ugh 1974 sugges tsa p ro f i t e s t im a t ed a t a ne t ga in pe r hec t a r e o f DM 3128 mi l l i on . Th i s c a l cu l a t i oninc luded a l l e s s en t i a l expense s l i ke s t ock f i sh , f e ed , l ime , e t c . , a s we l l a s t he cos t s o fe n e r g y , d e p r e c i a ti o n a n d l a b o u r . F i f t e e n p e r c e n t o f th e t o t a l e x p e n s e s w e n t i n t o f e ed .

C O N C L U S I O N S

T h e e x p e r i m e n t s o f 1 9 7 2 - 1 9 7 4 y i e l d ed a m a x i m u m c a r p w e ig h t g a in o f o v e r 1 5tonn e ha -1. How eve r , in i n t ens ive ca rp po nd f a rming , t he r e l a t i on be twe en y i e ld andcu l t i va t ed a r ea is no t t he on ly r e l evan t f a c to r . As we l l a s t he l im i t ing wa t e r supp ly ,t h e p o n d b o t t o m a r e a is i m p o r t a n t , m a i n l y f o r t h e p u r i f i c a ti o n c a p a c i t y .

T h e e x p e r i m e n t s g a v e s o m e i n d i ca t i o n s a s t o w h a t e x t e n t v a r i o u s p r o b l e m s c a ni n f l u e n c e i n t e n s i v e p r o d u c t i o n i n a c a r p p o n d , a n d w h a t d e m a n d s h a v e t o b e m e t b yt h is p a r t i c u l a r m e t h o d o f c u l t iv a t io n .

T h e p u r i f ic a t i o n c a p a c i t y o f th e e x p e r i m e n t a l p o n d w a s , a t ti m e s , o v e r e x e rt e d . I tis no t pos s ib l e t o conc lu s ive ly answer t he ques t i on r ega rd ing t he l im i t s o f i n t ens ivec u l t iv a t i o n o f c a r p p o n d s . E a c h p o n d r e a c t e d d i ff e r e n t ly . F l u c t u a t i o n s o c c u r e v e nf rom one yea r t o t he nex t s i nce t he c l ima t e ha s an ev iden t i n f l uence on t he b io -chem ica l p roces se s w i th in t he pon d . Thus , i t is ha rd ly pos s ib l e t o g ive de t a i ledgu ide l i ne s f o r s t ock ing dens i t y app l i cab l e t o p r ac t i c a l pond managemen t . Howeve r ,i n t e n s i ty s h o u l d b e s u c h t h a t i t t a k e s a d v a n t ag e o f j u s t a b o u t t h e m a x i m u m p u r if ic a -t i o n c a p a c i t y o f t h e p o n d . T h i s is s u p p o r t e d b y a e r a t io n w h i le e x c a v a t i o n o f e x c es s iv em ud l aye r s , dep l e t i ng t he o xyg en sup p ly , is a l so a pu rpose fu l me asu re . I n add i t i on , i t i sabso lu t e ly neces sa ry t o have wa t e r r e se rves ava i l ab l e i n o rde r t o avo id a dange rousd e t e r i o r a t io n o f p o n d w a t e r q u a li ty .

I n p r a c t ic e , i t i s r e c o m m e n d e d t o g r a d u a ll y a p p r o a c h t h e m o s t i n te n s iv e f o r m o fpon d cu l t i va t i on . Fo r t h is pu rpo se i n t e rm ed ia t e s t eps , i nvo lv ing sma l l e r r isk s , c an bet a k e n .

A ca r e fu l i n spec t i on o f t he f ish s t ock fo r d i s ea ses and pa r a s i t e s is e s sen t ia l . In t h i sr e spec t , h igh s t ock ing den s i t y i n sma l l pon ds i s o f advan t age .

F e e d i n g t e c h n iq u e s h a v e t o b e a d a p t e d c l o s e ly to t h e r e q u i r e m e n t s o f t h e c ar p , s otha t t he f i sh can f eed on dem and a nd l o sse s o f f e ed a r e avo ided . Dem and f eede r s so lveth i s p ro b l em ea s il y .

F ina l l y , i t is nece s sa ry t o keep a ca r e fu l check o n t he g row th r a t e o f the f ish andt h e f e ed c o n v e r s i o n , f o r w h e n a i m i n g f o r h i g h y ie l ds c o n n e c t e d w i t h h ig h p r o d u c t i o nc a r e fu l w a t c h h a s t o b e k e p t o n t h e e c o n o m i c s .


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REFERENCESKnosehe, R. (1973). Hydropneumatische Forderer zum Beluften yon Fischwasser. Z. Binnen-

f i s c he re i DDR, 20, 52-9.v. Lukowicz, M. (1973). Die Aufnahme yon Trockenfutt er im intensiv bewir tschaften Karp-fenteich. De r F i se hw i r t , 23, 79-83.v. Lukowicz, M. (1974). Intensiv Erzeugung yon Speisekarpfen im Teieh. De r F i sc hw i r t , 24,32-6.v. Lukowicz, M. (1975). Intensiv Aufzueht yon Satzkarpfen im Teieh. De r F i sc hw i r t, 25, 41-5.Toi, L, Shimadate , M. & Ito, T. (1960). Studies on intensive fish culture in farm ponds. I. Anexperimen t on oxygen depletion in carp ponds in relation to bott om mud. Bull. Fresh WaterFish. Res. Lab. , 10, 45-52.

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Lukowicz 1982 Aquacultural-Engineering