wickins 1985 aquacultural-engineering 2

7/28/2019 Wickins 1985 Aquacultural-Engineering 2

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Aquacu l tura l Eng ineer ing 4 (1985) 59-84

O r g a n i c a n d I n o r g a n i c C a r b o n L e v e ls i n R e c y c le dS e a w a t e r D u r i n g t h e C u l tu r e o f T r o p i c a l P r a w n sPenaeus sp .J .F . W i c k i n s

M inistry o f Agriculture, F isheries and F oo d, D irectorate o f Fisheries R esearch,F is he r ie s E x p e r i m e n t S t a t io n , C o n w y , G w y n e d d LL32 8UB, UK

A B S T R A C TSu spe nd ed p art icles and dissolved organic carbon in laboratory recirculat ionsys tem s were bro adly e ategorised by s i ze f i l t ra t ion an d ul t raviolet absorp-t ion . T h e i r c o n c en t r a t i o n s in recycled seawater increased dur ing the cul tureo f t ropical praw ns wi th increase in fee din g rate and also w i th a ' load 'f a c t o r ca l cu l a t ed t o t a ke a cco u n t o f t h e vo l u m e o f w a t e r u s ed t o cu l t u r ea kn o w n b io m a s s o f p r aw n s . I n s y s t em s o p er a t ed w i t h o u t p e r io d i c w a t e rrenewal t he pro por t ion o f organ ic ma t t er i n f i lt erab le m ater ia l and thein t egra ted u l t rav io l e t absorbance ( Z A 25 0- 33 0 nm ) o f f i l tra t e increasedwi th t ime. Th e increasing absorbanee observed, part icularly in the h igherw a ve len g th s ( ' A 2 9 0 - 3 3 0 n m ) , i n d ica t ed t h e a ccu m u l a ti o n o f m e t a b o l i-cally d eriv ed organic ma terial tha t was resistan t to micr obia l degradation.Mean num bers o f bacteria var ied imm ense l y f ro m 7 t o 2 5 0 0 0 103 m 1-1b u t w er e l o w er in f o a m ed t h a n u n f o a m ed s y s tem s .

The re la t ion be tw een the co ncen t ra t ion o f d i sso l ved inorganic carbon(a measure o f carbona te a l ka l in i ty ) and pH in t he sys t ems varied accord ingto the t y pe o f med ia in t he b io log ica l f i l t er and the m eth od used to con-t ro l pH. Resu l t s c loses t t o na tura l seawater were ob ta ined in sys t em scon ta in ing fi l ters w i th l imes tone m ed ia per iod ica ll y dosed wi th sod iumhyd rox ide so lu t ion . Higher l eve ls o f i norganic carbon for a g i ven pH abovep H 7 .9 were , h o w ever , n o t ed w h e n s o d i u m h yd r o x i d e w a s u s ed w i t hplast ic media f i lters , a featu re benef icia l to heavi ly loaded systems.

INTRODUCTIONDuring the last deca de man y valuable species of Crustacea have beencultured f o r o n e or more phases o f their life-cycle in land-based culture

59 Crown Copyright, 1985.


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60 J . F . Wick in ssystems (Chamberlain and Lawrence, 1981 ; Conklin e t a l . , 1981 ;Wickins, 1982). It is established that , in addition to the excretoryproducts of the cultured species, significant amounts of dissolvedand particulate material enter the water from food organisms (e.g.A r t e r n i a ; Moffett and Fisher, 1978) and from prepared foods soonafter immersion: around 22-30% of mass in 16 h (Forster, 1972); 31%of mass in 24 h (R. W. Sedgwick, 1979, pers. comm.); 20-30% of theprotein and lipid conten t in 1 h (Bages and Sloane, 1981); 11% ofprotein in 1 h (Cuzon e t a l . , 1982). Large pieces of uneaten food arereadily removed and such wastage may amount to as much as 32% ofthe daily ration (Wickins, 1985). Very few reports, however, havebeen published on suspended and dissolved organic wastes in marinerecirculation systems containing Crustacea (Wickins, 1981) despite theproblems such wastes may cause to experimenters (Bartley e t a l . , 1980).In the first part of this paper these materials are broadly categorised byfiltration and ultraviolet absorption; their concentrations are related tothe daily food ration and to a 'load' factor which takes into account inits calculation the biomass of animals cultured and the total quantityof water used during the culture period. The effects of dispersed airflotation (foaming) (Wheaton e t a l . , 1979; Lawson and Wheaton, 1980)on organic materials were observed in trials made with model recircula-tion systems and are also reported.

Percolating biological filters are widely used in recirculation systemsfor the oxidation of organic wastes and ammonia (Tiews, 1981), theoxidation being accomplished by microbial slimes and bacteria coatingthe surfaces of the filter media. Although carbonic acid is formedduring the oxidation of organic wastes it is the continuous productionof H + ions during the oxidation of ammonia which leads to a declinein inorganic carbon levels (carbonate alkalinity) in recycled seawater.In lightly stocked display aquaria the decline may take many months(Spotte, 1979; Bower e t a l . , 1981) but under extreme conditions canoccur in only a few days, particularly when senescent limestone (Siddall,1974), plastic or otherwise inert media is used in the biological filters(Wickins and Helm, 1981 ; Wickins, 1983). In addition to more frequentseawater replacement, methods used to combat reduced pH and carbon-ate alkalinity in marine systems include periodic replacement of lime-stone or shell filter media, additions of soluble alkalis, carbonate andbicarbonates and the incorporation of de-nitrification and algal culture


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Organic/inorganic C levels in recycled seawater during prawn culture 61units. The second part of this paper reports the relationships betweendissolved inorganic carbon levels and pH that were observed whendifferent combinations of filter media and chemical additives were usedduring the long-term culture of tropical penaeid prawns in laboratoryrecirculation systems.

METHODSC u l t u r e s y s t e m sObservations were made on 16 laboratory recirculation systems (875-10 627 litres capaci ty) in which marine penaeid prawns were culturedfor periods o f 28-352 days. In addition, four model systems (190 litrescapacity), also containing prawns, were used in 20 trials, each lasting51-72 days. During some trials dispersed air flotation treatment wasincorporated in two of the model systems (Fig. 1). Details of all thesystems are given in Table 1.

/C o ns ta nt h e a d 1 1 . 5 1 ra in - 1

c h a m b e r ~P e r c o l a t i n gb io lo gic al ~ _f i l ter( 15cm dia)

Air l i f t tubeA i r - -

=

F i g . 1 .

1 . 2 I r a i n - 1 1

Cul ture tank ; ~ "r 7i i

A irl if ttube

lAir J ~ Air

D i s p e r s e d airf lo tat ion co lumn/ / (5cm d ia )

- - S i n t e r g l a s sJ air stone// /

A m o d e l r e c i rc u l a t io n s y s t e m ( 1 9 0 litr e c a p a c i t y ) in c o r p o r a t i n g a p e r c o l a t-i n g b i o l o g i c a l f il te r ( 4 l it r e c a p a c i t y ) a n d a d is p e r s e d a ir f l o t a t i o n ( f o a m ) t o w e r( 1 . 5 4 l i t r e c a p a c i t y ) .


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TABLE1

TVume(eoCueT

aWaeTemeUsnhLaoyRcaoSems

On t3

Nmbosyems

1

1

1

2

1

4

1

3

1

1

4

Nmboas

3

1

1

4

1

4

1

3

1

1

2

Tasyemvume1685

39

29

26

15

14

10

10

8

1

Tavumowe

incuea

1469

7

13

20

8

8

4

3

4

1

Tavumeaowe

temeus

2

16

42

15

5

6

5

6

6

4

45

Temeuvume

aapcaoh

syemvum

2~

1

8

5

2

4

4

5

6

5

2b

Pcanfevume

(e

2

2

10

1

2

2

1

1

8

7

4

MeaL=meo

45%vd

P=pac9%vd

L

P

L

L

L

L

P

P

L

L

P

Hacoo

pcanfe

(mmad-1)

12

1

2

1

1

1

1

1

2

1

5

Ao

me

c

faoD=da

toma

ehswm

pfdeW-=sy

thcwn

-

W

.

.

.

.

D

D

-

-

W

Dsp

afoao

-

x

.

.

.

.

.

.

.

.

x

Cua

boma(k

psyem

072618203704

02uo012uo192100080000

aInuvumeo

ebpcanfemea

bAmasreenwerevnnsaecuea


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Organic~inorganic C levels in recy cled seawater du ring praw n cul ture 63S y st em m a n a g e m e n tS a l in i ty a n d t e m p e r a t u r e r a n g e d a s f o l lo w s : 2 6 - 3 4 % o a n d 2 8 + 2 C ,r e s p e c t i v e l y .

S e t t l e d s o l id s w e r e r e m o v e d d a i l y b y h a n d n e t o r si p h o n a n d s us -p e n d e d s o l id s b y t h e m e c h a n i c a l f i l te r in g a c t i o n o f g r av e l, p e r c o l a t in gf il te rs ( w h e n u s e d ) an d s y n t h e t i c w o o l w a d d i n g w h i c h w a s w a s h e dd a il y. I n s o m e tr ia ls p r o p r i e t a r y h ig h - ra te d i a t o m a c e o u s e a r t h , s w i m -m i n g p o o l f il te r s w e r e u s e d i n t e r m i t t e n t l y f o r a b o u t 2 h d a y -~ s o m e4 - 6 h a f t e r f e e d in g . S u c h f i lt e rs r e m o v e d 7 0 - 8 0 % o f p a r t ic l e s d o w n toa b o u t 5 # m in s iz e . F u r t h e r d e t a il s o f t h e s y s t e m s a n d th e i r m a n a g e -m e n t a r e g i v e n i n B e a r d a n d F o r s t e r ( 1 9 7 3 ) ; B e a r d e t a l . ( 1 9 7 7 ) ; W i c k i n sa n d B e a r d ( 1 9 7 8 ) ; S e d g w i c k ( 1 9 7 9 ) ; B e a r d a n d W i c k in s ( 1 9 8 0 ) .

F e e d i n g a n d c a l c u la t io n s o f g r os s a n i m a l lo a dF o o d w a s g i ve n o n c e e a c h d a y in t h e m o r n i n g , a n d w a s a d j u s t e d s o t h a ts o m e r e m a i n e d u n e a t e n t h e n e x t d a y . G e n e r a l ly a 5 0 : 5 0 m i x t u r e o ff r e s h l y s h u c k e d m u s s e l M y t i l u s e d u l i s g . a n d f r o z e n s h r i m p C r a n g o nc r a n g o n g . w a s g iv e n b u t w h e r e p e l le t s w e r e f e d t o th e p r a w n s t h e s ew e r e o b t a i n e d f r o m J a p a n ( T a i y o G y o G y o C o . L t d ) . F e e d i n g r a te ( F )w a s e x p r e s s e d a s t h e d r y w e i g h t o f f o o d f e d p e r d a y a s s u m i n g ana v e ra g e w a t e r c o n t e n t o f 8 3 % f o r m u s s e l , 7 2 % fo r s h r i m p a n d 5 % f o rp e l l e ts ( W i c ki n s, 1 9 8 5 ) . D i s so l v e d a n d s u s p e n d e d w a s t e s f r o m p e l l e t-f e d a n d s h e l l f i s h - f e d p o p u l a t i o n s w e r e n o t d i s t i n g u i s h e d s i n c e t h e p o p u -l a t i o n s w e r e o f t e n c u l t u r e d w i t h i n t h e s a m e r e c ir c u l a t i o n s y s t e m .

T h e g r o ss a n i m a l l o a d p l a c e d o n a s y s t e m w a s c a l c u l a t e d f r o m t h ew e i g h t o f a n i m a l s ( b i o m a s s ) h e l d , d i v i d e d b y t h e t o t a l v o l u m e o f w a t e ru s e d (i n c l u d in g t h e i n it ia l v o l u m e o f t h e s y s t e m ) t h r o u g h o u t t h e c u l t u r ep e r io d . W h e r e t h e b i o m a s s i n c re a s e d m a r k e d l y d u e t o g r o w t h o f th ea n i m a l s, a n a l l o w a n c e f o r t h e i n c r e a s e d b i o m a s s w a s m a d e i n t h e c a lc u -l a t io n . F o r e x a m p l e , 5 7 7 l it re s o f w a t e r f r o m a 3 9 5 3 l i tr e c a p a c i t yr e c i r c u l a t io n s y s t e m ( T a b l e 1, c o l u m n 3 ) w e r e r e p l a c e d w i t h c l e anw a t e r t w i c e e a ch w e e k d u r in g a n 8 4 - d a y g r o w t h e x p e r i m e n t . T h e t o t a lv o l u m e o f w a t e r u s e d w a s t h e r e f o r e :

3 9 5 3 + 8 4 = 1 7 8 0 1 l i tr e s7


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64 J . F . W i c k i n sD u r i n g t h e t ri al b i o m a s s i n c r e a s e d f r o m 2 4 8 g o f j u v e n i l e p r a w n s ( 0 . 2 9 gm e a n liv e w e i g h t ) t o 3 7 2 4 g o f 7 g p r a w n s . T h e b i o m a s s i n c re a s e w a st h e r e f o r e

3 7 2 4 - - 2 4 8 = 3 4 7 6 ga n d t h e g r o s s a n i m a l l o a d

3 4 7 6 = 0 -1 9 5 g l i t r e -11 7 8 0 1A n a l y t ic a l m e t h o d sT h e m e t h o d s u s e d f o r t h e m e a s u r e m e n t o f t e m p e r a t u r e , s a li ni t y, p H ,d i s s o l v e d o r g a n i c a n d i n o r g a n i c c a r b o n p a r t i c u l a t e s a n d b a c t e r i a w e r et h e s a m e a s t h o s e d e s c r i b e d b y W i c k in s a n d H e l m ( 1 9 8 1 ) . M e a s u r e m e n t so f d i s s o l v e d i n o r g a n i c c a r b o n w e r e a s s u m e d t o g iv e a g o o d i n d i c a t i o n o ft h e c a r b o n a t e a l k a l i n it y o f r e c y c l e d s e a w a t e r o v e r t h e p H r a n ge 8 . 2 - 6 - 6 ,s in c e b i c a r b o n a t e a n d c a r b o n a t e i o n s a re t h e p r i m a r y b u f f e r s in se a -w a t e r a n d c a r b o n d i o x i d e ( in e q u i l i b r i u m w i t h t h e a t m o s p h e r e ) c o n s t i-t u t e s l es s t h a n 2 % o f t h e t o t a l d is s o l v e d i n o r g a n i c c a r b o n p r e s e n t( W h i t f i e l d , 1 9 7 4 ) .

F o r p r a c t i c a l r e a s o n s n o t a ll o f th e a n a l y s e s c o u l d b e m a d e o n a ll t h es y s t e m s . F o r e x a m p l e , i n s o m e t ri a ls , p a r t i c u l a t e s l a rg e r t h a n 1 ta m , a n dd i s so l v e d o r g a n i c c a r b o n , w e r e m e a s u r e d o n c e o r tw i c e w e e k l y , w h i le ino t h e r s s u b - m i c r o n p a r t i c u l a te s a n d u l t ra v i o l e t a b s o r p t i o n w e r e a ls om e a s u r e d .

S u s p e n d e d p a r t i c u l a te a n d d i s s o lv e d o r g a n ic m a t t e r w e r e c a t e g o r i s e di n t o f o u r c o m p o n e n t s :

( i) M i c r o - o r g a n i s m s a n d p a r t i c l e s l a r g e r t h a n l ta m r e t a i n e d o nW h a t m a n G F / C f i l te r p a p e r . T h e o r g a n i c c o n t e n t o f t h is m a t e r ia lw a s d e t e r m i n e d b y a s h in g s a m p l e s a t 5 0 0 C f o r 2 4 h i n a m u f f l ef u r n a c e ( S t r i c k l a n d a n d P a r s o n s , 1 9 6 8 ) .( i i ) S u b - m i c r o n p a r t i c u l a t e m a t e r i a l , w h i c h i n c l u d e d s o m e b a c t e r i aa n d c o l l o i d s , r e t a i n e d o n 0 . 2 2 t a m M i l l i p o r e f i l t e r s .

( ii i) 'D i s s o l v e d ' o r g a n i c c a r b o n o r c a r b o n a c e o u s m a t e r i a l p a s s in gt h r o u g h W h a t m a n G F / C f il te rs an d m e a s u r e d b y r a p id c o m -b u s t i o n a t 9 5 0 C o n a B e c k m a n m o d e l 9 1 5 t o ta l c a r b o n a n a l ys e ra n d c o r r e c t e d f o r i n o r g a n i c c a r b o n c o n t e n t .


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Organic~inorganic C levels in recycled seawater during prawn culture 65( iv ) 'D i s s o l v e d ' o r g a n ic m a t e r ia l w h i c h p a ss e d t h r o u g h W h a t m a n

G F / C f i l te r s a n d a b s o r b e d u l t r a v i o l e t l ig h t o v e r t h e w a v e l e n g t h s2 5 0 - 3 3 0 n m . I n t e r f e r e n c e f r o m t h e h ig h n i t ra t e l ev e ls t h a t a ree x p e c t e d in re c y c l e d s e a w a t e r w a s a s s u m e d t o b e m i n i m a l a tt h e se w a v e l e n g th s ( F o s t e r , 1 9 7 4) . M e a s u r e m e n t s o f a b s o r b a n c ew e r e m a d e u s i n g a U n i c a m S P 5 0 0 s p e c t r o p h o t o m e t e r in 1 0 c ms i li c a - fa c e d c e ll s a g a i n s t a r e f e r e n c e c e ll c o n t a i n i n g p h o t o -o x i d i s e d d i st il le d w a t e r . Q u a n t i t a t i v e a s s e s s m e n t s o f t h e i n te -g r a te d a b s o r b a n c e o v e r s e l ec t e d ra n ge s o f w a v e l e n g th s ( 2 5 0 - 2 9 0a n d 2 9 0 - 3 3 0 n m ) w e r e m a d e u sin g S im p s o n ' s a p p r o x i m a t i o nf o r a r e a u n d e r a c u r v e :

a re a = ~ h (Yl + 4y2 + Y3)w h e r e 2 h = d i s ta n c e b e t w e e n Y l a n d Y3 a n d y = w a v e l e n g t h .

S t a t i s t i c a l m e t h o d sP r o b a b i l i t y v a l u e s g iv e n in t h e t e x t r e f e r to c o m p a r i s o n s o f m e a n s an dr a t e s lo p e s m a d e u s in g S t u d e n t ' s t t e s t.

W e i g h t e d r e g r e ss io n a n a l y si s ( D r a p e r a n d S m i th , 1 9 6 6 ) w a s a p p l i e dt o t h e i n o r g a n ic c a r b o n p H d a t a i n F i gs 5 ( A ) - ( F ) ( T a b l e 2 ). D a t a w e r eg r o u p e d b y p H in te r va ls o f 0 . 0 9 a n d c a r b o n c o n c e n t r a t i o n m e a n s an ds t a n d a r d e r r o r s d e r i v e d f o r e a c h p H i n t e rv a l .

R E S U L T SP a r t i c u l a t e a n d ' d i s s o l v e d ' o r g a n i c c a r b o n( i) Micro-organisms and particles larger than 1 tamT h e c o n c e n t r a t i o n s ( m g l it re - 1) o f fi l t e r a b l e m a t e r i a l l a r g e r t h a n 1 ta mw e r e m e a s u r e d o n e - t h r e e t i m e s e a c h w e e k i n s ix c u l tu r e tr ia ls w h i c hl a s t e d 4 - 3 7 w e e k s . M o n t h l y m e a n v a l u e s f r o m e a c h s y s t e m w e r e p l o t t e da g a in s t t h e m e a n d a i ly f o o d r a t i o n , F ( g d r y f o o d d a y - l ) , o v e r t h e s a m ep e r i o d s a n d a l t h o u g h v a r ia b le , t y p i c a l l y c h a n g e d w i t h c h a n g e in f e e d i n gr a te . R e g r e s s i o n a n a l y s is ( T a b l e 3 ) s h o w e d t h a t t h e o v er a ll m e a n ( ln )p a r t i c u l a t e c o n c e n t r a t i o n w a s a l so c o r r e l a t e d w i t h g r o s s a n i m a l l o a d .T h e r a ng e o f c o n c e n t r a t i o n s a m o n g i n d iv i du a l m e a s u r e m e n t s w a s1 . 5 - 3 5 . 5 m g l i t r e -1 a n d i n r e c ir c u l a t io n s y s t e m s c o n t a i n i n g p l a st ic


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66 J. F. WickinsT A B L E 2

Weighted Regression Analysis and Estimate of the Proportion of the Total VariationDue to Regression: Y = B x + C where Y= Mean Concentration of DissolvedInorganic Carbon (rag litre -1) and x = pH

Code B (s lope) C ( in tere ept) Correlation Proba bil i ty % Total(see tex t} coef f ic ient , (p < ) variation

r due toregression

a (pH > 7-5) 23.85 - 173.28 0.991 0.001 98-3c 21.64 - 151.13 0.954 0.001 91.0e 27.41 - 189.97 0.979 0.01 95.9b 8-90 -55-21 0.943 0.001 88.9d 10.92 -66.24 0.944 0.001 89.1f (pH ~< 7.8) 22.48 - 147.43 0.931 0.05 86.7f(pH >1 7.8) -2 4. 76 223.66 -0 .993 0.001 98.7

media filters separate, high-rate mechanical filtration was often neces-sary to clarify the water and reduce particulate concentration (seeDiscussion). The material retained on the G F / C filters was about 60%organic material with 40% of mineral ash. Considerable variation inthe organic content occurred between and within different recirculationsystems; the overall range encountered was 10.0-92.6%.

In fou r separate trials where the water was not changed fo r 56 days,the proportion of organic matter in the filterable material was found toincrease linearly with time (regression eqn (1), Table 4). No propor-tional increase in % organic matter with time was detected in systemswhere regular water changes were made.

The weight of organic materi al varied from 0.1 to 19.1 mg litre -1generally but two values of 31.2 and 34. 6 mg litre -1 were recor ded after44 days in one of the four trials in which the water was not changed.The concentrations recorded overall were predominantly within thelimits found in particulates from the laboratory seawater supply (0.9-19.4 mg litre-1).(ii) S u b - m i c r o n p a r t i c u l a t e m a t e r i a l a n d b a c t e r i aThe conc entr ati on of filterable sub-micron material was measured threetimes each week in four recirculation systems of approx imat ely I000


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Organic~inorganic C levels in recycled seawater during prawn culture 67T A B L E 3

Pred ic t ive Regress ion Equat ion Cons t an t s Descr ib ing the Increase i n Par t i cu l a t e and'Di sso lved ' Organ ic Mat t e r wi th Increase i n Feed ing Rate and Gross Animal Load

Parameter Slope Intercept Correlation Degrees p{In) coefficient offreedom

Pa rt icles > 1/ .tmIn m g l i tre -1 ( mo n t h l y

mean s) ver sus f eed ingra t e 0 -007 3 .21 0 .67 23 0 .0 01

Par t icles < 1> 0-22/amIn mg l i t re-1 ( mo n t h l y

me ans) ver sus f eed ingra t e 0 -02 0 .77 0 -54 18 < 0 . 05 > 0 -01

In mg l i t re -1 (ove ral lme an) ver sus l oad 15-27 2 .48 0 .95 4


10/26

68 J . F . W i c k i n sTABLE 4

Regression Equa tions Derived from Various Experimental T rials Described in theText

Textual Parameter Slope Inter- Corre- Degreesrefer- cept lation ofenee eoeffi- freedomcient

P

(1) % Organic matter versus days 0 . 6 2 37.77 0.80 30 '0.001(2) XA 250-330 versus days 1.07 22.56 0.80 30 '~0-001ZA 250-290(3) In versus days -0.12 In 2.43 0.95 29 ~0.001ZA 290-330(4) Particulates > 1 ~m

(rag litre -1) versus days 0.58 8.70 0.54 14


11/26

Organic~inorganic C levels in recycled seawater during prawn culture 69ing u p to 1 . 9 k g o f p r aw n s ) the mean numbers of bacteria ( 103m1-1)also increased throughout the culture period:

Replicate Weeks 1-28 Weeks 29-381 1674, SE = 568 3129, SE = 11112 1251,SE = 448 4570, SE = 1645

I

In two less densely stocked model systems (190 litre capacity)numbers were low, ranging from 54-1700 103 ml -~ (replica te means773, SE = 364 and 522, SE = 146 X 103 ml-1). An appare nt relation-ship existed between gross animal load and bacterial numbers but wasconsidered for tuit ous in view of the wide variation of bacterial numbersfrom week to week within the various systems. The effect of foamtreatment on bacterial numbers is described below.(iii) Carbonaceous material smaller than 1 lam and dissolved organiccarbonLevels of organic carbon were measured in four trials by combustion offiltrates from GF/C filters. Regression analysis showed that this frac-tion too was positively correlated with b oth feeding rate and grossanimal load and, in each of the three categories studied ((i)-(iii) above),a higher correlation coefficient was obtained when the fractions wereplotted against gross animal load than feeding rate (see Table 3 andDiscussion). The mean organic carbon content increased up to 16.7 mglitre -1 and was within the range no rmal ly found in the labora tory sea-water supply (0-5-1 8 mg litre-1).(iv) Material absorbing in the ultraviolet wavelength 250-330 nmMeasurements of absorbance over the wavelength range 250-330 nmwere made in two trials with the model recirculation systems. In eachtrial 70~ of the water was renewed thrice weekly in two o f the systems(group a), while in the remaining two (group b) the water was notchanged for eight weeks. In group a the integrated absorbance (2; A 250-330) fluctuated over the range 10.75-70.30 arbitrary units during thetrial. This contrasted with group b where the absorbance increasedlinearly with time from around 20 to 106 units (regression eqn (2) inTable 4).


12/26

7 0 J . F . W i c k i n sW h e n t h e i n te g r a t e d a b s o r b a n c e m e a s u r e d i n t h e r e c i r c u l a ti o n s y s t e m s

( g r o u p b ) w a s di v id e d i n t o t w o p o r t i o n s 2; A 2 5 0 - 2 9 0 a n d Z A 2 9 0 - 3 3 0 ,a g r e a t e r i n c r e a s e i n t h e Z A 2 9 0 - 3 3 0 p o r t i o n w a s a p p a r e n t a s t h e tr ia lp r o g re s s e d, p r e s u m a b l y a s m e t a b o l ic a l l y d e r iv e d m a t e r i a l a c c u m u l a t e d( s e e D i s c u s s i o n ) . T h i s i s s h o w n i n F i g . 2 w h e r e t h e r a t i o 22 A 2 5 0 - 2 9 0 /Z A 2 9 0 - 3 3 0 is s h o w n t o d e c r e as e w i t h t i m e . T h e b e s t r e la t io n s h ip f o rt h e c o m b i n e d d a t a f r o m t h e t w o t ri al s is g i ve n b y e q n ( 3 ) i n T a b l e 4 .

A t t e m p t s w e r e a l so m a d e w i t h t h e g r o u p b d a t a t o r e la t e t h e o b s e r v e dc h a n g e s in a b s o l u t e a n d r e l a ti v e a b s o r p t i o n w i t h i n t h e t w o w a v e l e n g t hg r o u p s t o t h e m e a s u r e d p a r t i c u l a t e a n d ' d is s o l v e d ' o r g a n i c f r a c ti o n s ino r d e r t o e x a m i n e f u r t h e r t h e p o s s i b le or ig i ns o f t h e l ig h t a b s o r b i n gs u b s t a n c e s . T h e a b s o r b a n c e w a s f o u n d t o i n c re a s e a s t h e o r g a n i cp o r t i o n o f p a r t i c u l a t e s r e t a i n e d o n t h e G F / C f i l te r p a p e r s in c r e a s e d , a n da ls o a s t h e c o n c e n t r a t i o n o f s u b - m i c r o n p a r t i c u l a te s i n c re a s e d . P l o t s o fc o n c e n t r a t i o n a g ai ns t a b s o r b a n c e ( d e g re e s o f f r e e d o m = 2 9 i n e a c hc a s e ) g a v e m a r g i n a l l y h i g h e r c o r r e l a t i o n c o e f f i c i e n t s ( r ) f o r 22 A 2 9 0 - 3 3 0t h a n f o r E A 2 5 0 - 2 9 0 ( T a b l e 5 ) . T h e v a lu e s o f r o b t a i n e d w e r e , h o w -e v e r, le ss th a n t h e v a l u e o b t a i n e d w h e n t h e a b s o r b a n c e r a ti o w a sp l o t t e d a g a i n s t t i m e ( r = 0 . 9 5 , s e e e q n s ( 2 ) a n d ( 3 ) , T a b l e 4 ) i n d i c a t -

._o

c~. Q

. Q 1/~m ND NDParticulates < 1/~m ND ND'Dissolved' organic carbon ND NDUltraviolet absorption, 2;A 250-290 and2;A 290-330 (means) Low High

NA 250-290Ultraviolet absorption, ' High LowNA 290-330 (ratxo)Correlation between ZA 250-290 and 'dissolved'

organic carbon +veNumbers of bacteria Low

No correlationND

Fast increase

No correlationHigh

ND, no differences observed.

Thus, in systems where the water was not changed foaming tended toslightly increase the levels of filterable particulates and reduce the rateof acc umula tion of 'dissolved' organic carbon.

Ultraviolet light absorption increased equally with time in bothfoamed and unfoamed systems in group c, but in group d absorbancefluct uated and mean values tended to be lower in foam ed systems(p > 0.05 < 0.1). The ratio of the integrated absorbances in group dwas higher in foamed than in unfoamed systems and was also lessvariable (Table 7). Possibly fo aming removed some o f the light absorb-ing material and also propo rti ona tel y more of the fr action (of metabolicorigin) that absorbed strongly at the higher wavelengths. In this context


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74 J. F. WickinsT A B L E 7

The Effect of Dispersed Air Flotation Treatment on Absorbance of UltravioletLight by Recycled Seawater

Foamed Not foamedNumber of experiments (group d, water regularly

renewed) 2 2Mean absorbance, ZA 250-290 14.58 19.1395% Confidence limits of mean 12.44-16.72 16.21-22.05Degrees of freedom 31 31Mean absorbance, ZA 290-330 7.56 11.8095% Confidence limits of mean 6.00-9.12 9.11-14.49Degrees of freedom 31 29

ZA 250-290Ratio, 2.04 1.81XA 290-33095% Confidence limits of mean 1.96-2.12 1.69-1.93Degrees of freedom 30 30Coefficient of variation (%) 11.4 18.2

it was noticed that the integra ted absorbance at the lower wavelengths(Z A 250-2 90 but not Z A 290-33 0) generally varied pro port iona tel ywith 'dissolved' organic carbon levels in the foamed but not in theunfoamed systems (see Discussion). The regression eqn (5) describingthe r elationship is given in Table 4.

Despite the wide variation in bacterial numbers, a series of count smade at intervals of at least one week indicated that foaming eitherexpelled or inhibited the devel opment of bacteria in both groups c and d:

Foamed Not foamedNumber of bacteria ml -a (mean of two replicates) 56 595t statistic 3.75

Degrees of freedom = 26, p < 0-001C a r b o n a t e a l k a li n i t y a n d pH(i) Reduction in carbonate alkalinityChanges in levels of pH and inorganic carbon that occurred in themodel recirculation systems during the culture of 26-57 g of tropical


17/26

Organic~inorganic C evels n r ecycled seawater during prawn cul tur e 75p r a w n s ( 1 - 5 g l iv e w e i g h t ) a re s h o w n i n F i g . 4 . In t w o t r ia ls a t h r ic ew e e k l y r e p l a c e m e n t o f 7 0 % o f t h e s e a w a t e r w a s s u f f i c ie n t t o p r e v e n tm a j o r c h a n g e s in p H a n d i n o r g a n i c c a r b o n l ev e l s o v e r a 5 6 d a y p e r i o d( F i g . 4 , l in e s ( a ) a n d ( c ) ) . I n f o u r o t h e r t ri al s w h e r e t h e w a t e r w a s n o t

3 0 1 02 5 1 o , , aI ~ k - - - . _ . o ~ . "

~O

b0 4 ; 1 '2 1 ; 2 ; 214 2 '8 312 3v6 4 ; 4 '4 4 '8 ;2 .56

8 .4 D a y sB 1a .2 J ~ . l k . . 8 0 !7 . 8 O 0 ~ ~ 0 07 . 6 -7 .4 - 0 ~ 0 " ~ 0 ~ 0, o o o

6.6 d6 .6 - 0 ~ ' - - - - ~ 0 06 . 4 - 0 0 0 0

' 6 . 2 -6 .0 ' ' 1 ' 2 ' ' 2 . . . . . . 5 14 8 1 6 2 0 4 2 6 3 2 3 6 4 0 4 4 4 8 2 5 6

D a y s

Fig. 4 . The chan ges in levels of (A ) inorganic carbon and (B) pH during n i tr i fica-t ion in recirculation system s with regular seawater renewal ( l ines (a) and (c) ) andwith no renewal ( l ines (b) and (d)) .


18/26

76 J. F. Wickinsc h a n g e d ( l i n e s ( b ) a n d ( d ) ) , t h e p H f e l l f r o m 8 . 2 t o 6 . 6 a n d c a r b o nf r o m 2 5 t o 2 m g l it r e -1 i n 4 0 d a y s , a l o ss o f a b o u t 0 . 6 m g c a r b o n l i t r e-1d a y -1 . T h e m e a n r a t e o f c a r b o n l os s C ( r a g l i tr e - I d a y - ~) w a s li n e a r l yr e l a te d t o t h e m e a n w e i g h t o f f o o d f e d c a l c u l a te d i n t e r m s o f i ts n i t ro g e nc o n t e n t , F N ( g d a y - l ; W i c k i n s , 1 9 8 5 ) a n d is d e s c r i b e d b y e q n (6 ) i nT a b l e 4 .( i i ) I n o r g a n ic c a r b o n / p H r e la t io n s h ip sW h e n a ll r e c i r c u l a t i o n s y s t e m s w e r e c a t e g o r is e d a c c o r d i n g t o t h e t y p eo f f i l t e r m e d i u m a n d c h e m i c a l s u s e d t o c o n t r o l p H a n d a l k a l in i t y i t w a sn o t i c e d t h a t t h e r e l a ti o n b e t w e e n t h e c o n c e n t r a t i o n o f di ss o lv e d in -o r g a n i c c a r b o n a n d p H v a r i e d (F i g. 5 ). I n m o s t o f t h e s y s t e m s a p r o p o r -t i o n o f th e w a t e r w a s c h a n g e d e a c h w e e k . S i x c o n d i t i o n s w e r e i d e n t i f i e db y t h e f o l l o w i n g c o d e s :

Fil ter me dium Chemical addi t ionsNo n e S o d i u m S o d i u m

carbonate/ hydroxidebicarbonate

Plast ic A (water no t renew ed) C ELimestone gravel B D FT h e l ar ge n u m b e r o f d a t a p o i n t s a n d t h e f r e q u e n t a s s o c ia t io n o f

v a l u es o f t h e i n d e p e n d e n t v a r ia b le ( p H ) w i t h m o r e t h a n o n e v al ue o ft h e d e p e n d e n t v a r ia b le ( i n o r g a n ic c a r b o n c o n c e n t r a t i o n ) c a ll ed f o rg r o u p i n g a n d t h e u s e o f w e i g h t e d r eg r e s s io n an a l y s is i n o r d e r t o p r e s e n ta c le a r p i c t u r e f o r e a c h c o n d i t i o n ( se e M e t h o d s ) .C o n s i d e r i n g f i r s t l y s y s t e m s i n w h i c h t h e f i l t e r m e d i a d i d n o t c o n t r i -b u t e t o t h e a l k a l i n e r e s e r v e , i . e . p l a s t i c m e d i a , a s p H d e c r e a s e d c a r b o nl e ve l s f e ll m a r k e d l y ( F i gs 5 ( A ) , ( C ) a n d ( E ) ) a n d t h e r e w e r e n o s ig n if i-c a n t d i f f e r e n c e s b e t w e e n t h e s l op e s a b o v e p H 7 - 4 r e g a r d le s s o f c h e m i c a la d d i ti o n s . H o w e v e r , t h e c o m b i n e d d a t a c o u l d n o t b e r e p r e s e n t e d b y ac o m m o n l in e s i n ce th e t h r e e i n t e r c e p t s w e r e s i g n i fi c a n t ly d i f f e r e n t( t t e st , p < 0 - 0 5 ) ; f o r e x a m p l e , a t p H 8 .0 d i ss o lv e d i n o r g a n ic c a r b o nl ev e ls w e r e h i g h e s t ( 3 0 m g l it re -1 ) w h e n s o d i u m h y d r o x i d e w a s u s e d( F ig . 5 ( E ) ) ; l e ss ( 2 2 m g l it r e - 1) w i t h s o d i u m c a r b o n a t e a n d b i c a r b o n a t e( F i g . 5 ( C ) ) ; a n d l o w e s t ( 1 7 . 5 m g l i tr e - 1) w h e n 11o c h e m i c a l s w e r e a d d e d( F i g . 5 ( A ) ) .


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O r g a n i c ~ i n o r g an i c C l e vel s i n r e c y c l e d se aw a t er d u r i n g p r a w n c u l t u r e 7 7

c3coc

30

20

1 0 -

0

30 .

10

B

i i

A

D

J, i

7.4 7.8 8.2

F

C

/i i l i

7.0 7.4 7.8 8.2pH

i

fO i i , v

6.6 7.0 7.0 7 , 4 7.8 8.2pH pH

F i g . 5 . T h e r e l a ti o n s h ip b e t w e e n p H a n d i n o r g a n ic c a r b o n c o n c e n t r a t i o n i n s ea -w a t e r r e c y c l e d f r o m ( A ) p l a s t i c m e d i a f i l te r s ; ( B ) l i m e s t o n e g r av e l f il te r s ; ( C ) p l a s t icm e d i a f i lt e rs d o s e d w i t h s o d i u m c a r b o n a t e / b i c a r b o n a t e s o l u t i o n ; ( D ) l i m e s t o n eg ra ve l f i lt e rs d o s e d w i t h s o d i u m c a r b o n a t e / b i c a r b o n a t e s o l u t i o n ; ( E ) p l a s ti c m e d i af il te r s d o s e d w i t h s o d i u m h y d r o x i d e s o l u t i o n ; a n d ( F ) l i m e s t o n e g r av el f il te r s d o s e d

w i t h s o d i u m h y d r o x i d e s o l u t i o n .

I n f i lt e r s c o n t a i n i n g a l i m e s t o n e m e d i u m , c a r b o n l e v e l s f e l l l e ssm a r k e d l y t h a n in f il te r s w i t h a p la s t ic m e d i u m f o l l o w i n g a r e d u c t i o nin p H . T h is w a s p r o b a b l y d u e to c o n t r i b u t i o n s m a d e b y t h e l im e s t o n et o s e a w a t e r a l k a l in i t y . T h e r e w e r e n o d i f f e r e n c e s b e t w e e n s l o p e s a m o n gs y s t e m s n o t d o s e d a n d s y s t e m s r e c e iv i n g s o d i u m c a r b o n a t e a n db i c a r b o n a t e , a n d a l t h o u g h c a r b o n l e v el s t e n d e d t o b e h i g h e r in d o s e ds y s t e m s t h e y w e r e n o t s i g n i f i c a n t l y s o .

P l as ti c a n d l im e s t o n e c o n t a i n in g s y s t em s d o s e d w i t h s o d i u m h y d r o x -i d e s h o w e d a s im i l a r r e l a t io n s h i p b e t w e e n p H a n d c a r b o n o v e r t h e p Hr a ng e 7 . 3 - 7 . 8 . A b o v e a b o u t p H 7 . 8 5 in p la s t i c f il te r s ( F ig . 5 ( E ) ) t h er e l a ti o n s h i p w i t h c a r b o n c o n c e n t r a t i o n c o n t i n u e d l in e a rl y. I n l i m e s t o n ef il te r s , h o w e v e r , a p r o n o u n c e d r e ve r sa l o c c u r r e d ( F ig . 5 ( F ) ) a n d l e v el s o fd i s s o lv e d i n o r g a n ic c a r b o n d e c l i n e d w i t h i n c r ea s in g p H ( s e e D i s c u s s i o n ) .


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78 J . F . W i c k i n s

In systems containing filters of plastic media where chemicals werenot added and pH was allowed to fall below pH 7.4 (Fig. 5(A)), aninflexion in the pH inorganic carbon relationship occurred at aroundpH 7.45 (see Discussion). No such inflexion occurred in limestonefilters, again, probably due to the contribution of the limestone tocarbonate alkalinity.(iii) Control o f pH and carbonate alkalinityUsing data from 11 culture trials, made with plastic media filters, thequantities of sodium hydroxide added to maintain pH (and, indirectly,carbonate alkalinity) were plotted against gross animal load. The Inweight (g) added per day per 100 litres of water used throughout theculture period increased in proportion to In load according to theregression eqn (7) in Table 4.(iv) Effect o f foaming on carbon dioxide and pHThe vigorous aeration employed in dispersed air flotation columnstypically assisted the loss of excess carbon dioxide from the waterwhich tended to normalise pH levels. This occurred in systems wheredissolved inorganic carbon levels were maintained (for example, byregular partial water changes) at 16-21 mg litre -~ during normal nitri-fication (Table 8).

DISCUSSIONParticulate and 'dissolved' organic materialOrganic substances arise not only from the cultured animals and theiruneaten food but also from the metabolic activity of microorganismsattached to suspended solids and filter surfaces. Most of the micro-organisms are likely to be heterotrophic and will increase in numbers inproportion to the available organic (nutrient) substrate concentration(SSrner, 1981).

In a number of systems, levels of particulates increased with time asthe daily feeding rate increased. When animals were removed fromsystems for experiments, food input was reduced accordingly. For thisreason levels of particulates, dissolved organic carbon and perhaps


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Organic~inorganic C levels in recycled seawater during prawn cultureT A B L E 8The Effect of Foaming on Carbon Dioxide and pH Levels

79

Replicate Foamed Not foameda b c d

Carbon dioxide (mean mgCO2-C litre-1) 0.08 0.0795% Confidence limits of mean 0.07-0.09 0.06-0.07

Mean pH calculated from [H ] 8.18 8.1195% Confidence limits of mean 8-1%8-19 8.08-8-15

0-14 0-120.12-0.16 0-10-0.148.00 7.977.98-8-03 7.94-8-01

Degrees of freedom = 24 in each case.

bacteria were more closely related to feeding rate than to time. The low(though significant) correlation coefficients obtai ned (0.54-0 .67) fromplots of particle concentration against feeding rate were probably dueto differing water renewal rates and to the inter mitt ent use of diato-maceous earth filters in some of the systems. Only a general trendtowards higher concentrations with increased feeding rate was thereforeshown. Higher correlation coefficients (0.81, 0.84) were obtained whenthe overall mean concentrations were compared with gross animal loadsin the systems, a figure which acc ounte d for differe nt rates of waterrenewal. At high gross animal loads mechanical filters that operatedindependently of biological filters were convenient to use becausefiltered material could be removed without disturbing biologicallyactive slimes.Trials made w i t h o u t p e r i o d i c w a t e r r e n e w a lUnder comparable conditions of animal load, whether the water waschanged or not seemed to have little effect on concentration of particu-lates and dissolved organic carbon. When the water was not changed,however, the proportion of organic matter in material retained on GF/Cfilters and the i ntegrated ultraviole t absorbance (particularly I A 290 -330) increased with time.Changes in the composition or origin of dissolved organic material

in seawater have been indicated from seasonal changes which occur in


22/26

80 J . F . W i c k i n sthe ultraviolet absorption characteristics of natural seawater (Fosterand Morris, 1971 ; Foster and Foster, 1977). In systems where the waterwas not changed there were also significant but more variable positivecorrelations between 2; A 290-330 and the percentage of organic matterin material retained on the GF/C filters and between ~ A 290-330 andlevels of sub-micron particulates. Although little can be said concerningthe characterisation of the substances absorbing the ultraviolet light,the results seem to confirm the findings of Foster and Morris (1971)who suggested that the greater absorbance which occurred at longerwavelengths in coastal seawater during au tumn (~; A 275-300) was dueto organic matter derived from i n s i t u biological activity rather thanfrom land drainage material which absorbed strongly at lower wave-lengths.

The accumulation of dissolved organic material, 'yellow substance',derived from fish foods which absorbed strongly at 315 nm and also ofcoloured, filterable particulate matter in very densely stocked recircu-lation systems was described by Rosenthal e t a l . (1978), who used thedissolved 'yellow substance' as an indicator of the levels of non-bio-degradable compounds which accumulated in the water. Although thewater did not appear yellow in the present marine systems run withwater renewal, the integrated absorbance Y. A 290-330 included a com-ponent due to the accumula tion of metabolically-derived materialwhich was resistant to microbial degradation both by slimes in thebiological filters and by suspended microorganisms. Ozone was usedsuccessfully by Rosenthal e t a l . (1978) to degrade such refractoryorganic substances into components which were then oxidised inpercolating biological filters.

The reversal in the relationship between absorbance ratio and 'dis-solved' organic carbon shown in Fig. 3 was probably an artifact causedby the t emporary increase in the ratio during days 19-31 (see Fig. 2).The increase indicated that absorbance by material of metabolic originmight have become temporarily of less importance in the presence ofmaterial from other (unidentified) sources. Examples of possiblesources might include contaminated distilled water added to counte ractevaporative losses or organic aggregations released from filters.Carbonate a lkal inity and pHLoss of alkalinity during water treatment in marine aquaria was quanti-fied by Hirayama (1974) who showed that the rate of loss V(equivalents


23/26

O r g a n i c~ i n o rg a n i c C l e v e ls i n r e c y c l e d s e a w a t e r d u r i n g p r a w n c u l t u r e 8 1day 1) was related to the weight of food fed F (g day- l): V -- (2.52 +0.92F) x 10-3. A similar slope value (0.79) was found for the relationshipbetween weight of sodium hydroxide used to maintain pH and animalload in the laboratory systems. The ratio of inorganic carbon loss tonitrogen input rates in the present trials was 0.99, close to that pre-dicted stoichiometrically (0-948) and within the range 0.76-1.24 foundin model marine filters dosed with ammonium chloride solutions(Wickins, 1983).

It is important to consider the relationship between pH and inorganiccarbon in recycled seawater with reference to the method of pH controland nature of the filter media. In the laboratory filters neither mediumemployed prevented acidification: but it was found that results closestto natural seawater, which at pH 8.0 contains about 26 mg inorganiccarbon litre -1, were obta ined with limestone filters dosed with sodiumhydroxide solution (25 mg carbon litre-1). Greater reserves of carbonatealkalinity (30 mg carbon litre -1) were obtained at the same pH whensodium hydroxide was used with plastic media filters, presumably asconditions favoured the entry of respiratory and atmospheric carbondioxide into the bicarbonate-carbonate system (Wickins, 1983).

Two features of Figs 5(A) and (F) are worthy of comment. Theinflexion in the pH/inorganic carbon relationships shown in Fig. 5(A) isan artifact of the regression analysis. The relationship is perhaps betterillustrated by a curve over the pH range 7.4-7.7 within which seawaterbuffering is minimal (Whitfield, 1974). In Fig. 5(F) the decline indissolved inorganic carbon levels with increasing pH above pH 7.85 wasprobably due to carbonates crystallising out of solution onto the lime-stone surfaces of the filter media (Weyl, 1967; Berner, 1975). Becauseof this, and the tendency of limestone filters to become blocked, theuse of sodium hydroxide with plastic media filters proved more reliableand predictable in laboratory systems where gross animal loads werehigh.Dispersed a ir f lota t ionPerhaps the most useful effects of dispersed air flotation were themarked reduction in bacterial numbers and the tendency to stabilise pH.

In single pass or through flow dispersed air flotation units (Wheatone t a l . , 1979), foaming generally results in a decrease in the concen tra tionof particulate material retained on GF/C filters and an increase in thatretained on the finer GF/F grade (Wickins and Helm, 1981). Under


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82 J. F. Wickinsr e c i r c u l a t io n c o n d i t i o n s t h e f r a c t i o n r e t a i n e d o n G F / C f il te r s i n c r e a se db u t t h a t r e t a i n e d o n 0 . 2 2 / a m M i l l i p o re f il te r s d i d n o t . I n t h e s y s te m o fR o s e n t h a l et al. ( 1 9 7 8 ) , t h e 0 . 2 2 / a m f r a c t i o n w a s r e d u c e d a f t e r d i s p e r s e da i r / o z o n e f l o t a t i o n t r e a t m e n t . I t w a s p o s s i b l e t h a t in r e c y c l e d s e a w a t e rt h e f i n e p a r ti c le k f o r m e d c o a r s e r a g g r e g a ti o n s o r t h a t t h e c o n d i t i o n s o ff o a m i n g a c t u a l l y g a ve ri se t o l a rg e r p a r t ic l e s ( J o h n s o n a n d C o o k e , 1 9 8 0 ) .

T h e e f f e c t o f f o a m t r e a t m e n t o n u l tr a v io l e t a b s o r p t i o n is n o t c le a ra l t h o u g h t h e r e s u lt s s u g g e s t t h a t f o a m i n g m i g h t h a v e r e m o v e d s o m ed i s so l v e d o r g a n i c m a t e r i a l w h i c h a b s o r b e d i n th e r a n ge ~ A 2 9 0 - 3 3 0 n m .T h e v a r ia b l e b u t s ig n i fi c an t ( p < 0 . 0 1 ) c o r r e l a t io n b e t w e e n i n t e g r a t e da b s o r p t i o n Z A 2 5 0 - 2 9 0 a n d d i s s o lv e d o r g a n ic c a r b o n l ev e ls in f o a m e ds y s t e m s l e ad s t o s p e c u l a t i o n t h a t f o a m i n g p r o d u c e d m a t e r i a l t h a ta b s o r b e d s t r o n g l y a t t h e s h o r t e r w a v e l e n g t h s c o n c u r r e n t l y i n c r e a s in gt h e a b s o r b a n c e r a t i o Z A 2 5 0 - 2 9 0 / Z A 2 9 0 - 3 3 0 in t re a te d s y s te m s .D e s p i t e t h e p r e s e n t u n c e r t a i n t i e s c o n c e r n i n g t h e a c t i o n o f f o a m i n g i ns e a w a t e r t h e i n c o r p o r a t i o n o f d i s p e r s e d a ir f l o t a t i o n i n to m a r i n er e c i r c u la t io n s y s t e m s s e e m s t o p r o v i d e b e n e f i t s w o r t h y o f f u r t h e r s t u dy .

R E F E R E N C E SBages, M. & Sloane, L. (1 981 ). Effe cts o f dietary prote in and starch leve ls on

grow th and survival of Penaeus monodon (Fab ricius) post-larvae. Aquaculture,25 , 117-28 .

Bartley, D. M., Carlberg, J . M., Van Olst , J . C. & Ford, R. F. (1980). Growth andconversion efficienc y of juvenile A merican lobsters (Homarus americanus) inrelat ion to temperature and feeding level . Proc. 11th Ann. Meeting Wld. Maricult.Soc., New Orleans, Louisiana, USA, 5-8 March, Louisiana State University,pp . 355-68 .

Beard, T. W. & Fors ter , J . R. M. (1973). A grow th experimen t withPenaeus mono-don Fab . in a closed system . ICES, Shellfish and Ben thos Co m m ittee, CM 1973K: 39, 6 pp. (mimeo).

Beard, T. W. & Wickins J . F. (1980). The breeding ofPenaeus rnonodon Fabriciusin labo rato ry recirculation systems. Aquaculture, 20 , 79-89 .Beard, T. W ., W ickins, J . F . & Arnstein, D. R. (1977). The breeding and growth ofPenaeus merguiensis de Man in labor atory recirculation systems. Aquaculture,10 , 275-89 .Berner, R. W. (197 5). T he role of magnesium in the crystal grow th of calci te andaragonite from seawater. Geochim. cosmochim. Acta, 3 9 , 4 8 9 - 5 0 4 .


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water cu l tu re sys t ems: l imi t a t i ons o f ca l careous f i l t r an t s . Aq u a cu l t u r e , 2 3 ,2 1 1 - 1 7 .C h am b er l a in , G . W . & L aw r en ce , A . L . (1 9 8 1 ) . M a t u r a t io n , r ep r o d u c t i o n an dg r o w t h o f Pen a eu s va n n a m e i an d P. styl irostris f ed na tu ra l d i e t s . J . W ld. Marl-cul t . Soc. , 1 2 ( 1) , 2 0 9 - 2 4 .

Con k l in , D . E . , B ordne r , C . E . , G ar re t t , R . E . & C of fe r R . J . (19811). Im prov edfac i li ti es fo r e xpe r ime n ta l cu l tu re o f lobs t e r s . J . W ld. Maricult . So c. , 12 (1 ) ,5 9 - 6 3 .

Cuz on , G . , Hew Meng , Cogn ie , D . & So le t chn ik , P . (1982 ) . T ime l ag e f f ec t o ffeed ing on g row th o f j uven i l e sh r imp Penaeus ]apon icus Bate . A q u a c u l t u r e , 2 9 ,3 3 - 4 .D r ap e r , N . R . & S mi t h , H . ( 1 9 6 6 ) . Ap p l i ed Reg r ess io n An a l y s i s, J o h n W i l ey & S o n s ,N e w Y o r k , p p . 7 7 - 8 1 .

F o r s t e r , J . R . M . ( 1 9 7 2 ) . S o m e m e t h o d s o f b i n d in g p raw n d i et s an d t h e i r e f f ec t o ngrow th and ass imi la t ion . J . Cons. perm. in t . Explor . Mer. , 3 4 ( 2 ) , 2 0 0 - 1 6 .

Fo s t e r , P . (197 4) . Ul t r a -v io le t abso rp t ion charac t e r i s t ics o f na tu ra l water s . War.Res . , 8 , 1 3 7 - 4 2 .

Fos t e r , P . & Fos t e r , G . M. (1977) . Ul t r a -v io l e t abso rp t ion charac t e r i s ti cs o f wa ter sin an indust r ial ized es tuary . W a t . Res . , 1 1, 3 5 1 - 4 .

Fos t e r , P . & M or r is , A . W. (1971 ) . T he use o f u l t r a -v io l e t abso rp t ion m easu rem en t sfo r t he es t im at ion o f o rgan ic po l lu t i on in i n shore sea water s . Wat . Res . , 5, 19-27.

Hi rayama, K . (1974) . Water con t ro l by f i l t r a t i on i n c losed cu l tu re sys t ems . A q u a -cu l ture , 4 , 3 6 9 - 8 5 .

Johnson , B . D . & Cooke , R . C . (1980) . Organ ic par t i c l e and aggrega t e fo rmat ionresu l t i ng f rom the d i s so lu t i on o f bubb les i n sea water . Limnol . Oceanogr. , 25( 4 ), 6 5 3 - 6 1 .

Law son , T . B . & W heaton , F . W. (198 0) . Rem oval o f o rgan ics f rom f i sh cu l tu rew a t e r b y f o am f r ac t i o n a t i o n . Proc. l l th An n. M eet in g W ld. Maricult . Soc. , N ewOrleans . Lou i s iana , USA , 5 -8 M arch , Lous i ana S t a t e Un iver s i t y , pp . 128-3 4 .

M o f f e t t , W . g . & F i s h er , W . S . ( 1 9 7 8 ) . A m m o n i a p r o d u c t i o n r a te s o f Ar t em i a s a l i n aunder var ious cu l tu re cond i t i ons . J. b i 'sh . Res. Bd Can., 3 5 , 1 6 4 3 - 8 .

R o s en t h a l , H . , K r f in e r , G . & O t t e , G . ( 1 9 7 8 ) . E f f ec t s o f o zo n e t r ea t m en t o n r ec i rcu -l a t i ng water i n a c losed f i sh cu l tu re sys t em. ICES, Mar i cu l tu re Commi t t ee , CM1978 F : 9 , 16 pp . (mimeo) .S~ irner, E . (19 81) . Rem oval o f d i s so lved and par t i cu l a t e o rgan ic m at t e r i n h igh-ra tet r ickl ing f i l t ers . W a t . Res . , 1 5 , 6 7 1 - 8 .

Sedgwick , R . W. (1979 ) . Ef fe c t o f r a t i on size and f eed ing f r eq ue ncy on the g row than d f o o d co n v e r s i o n o f j u v en il e Penaeus merguiensis d e M an . A q u a c u l t u r e , 16,2 7 9 - 9 8 .S idda ll , S . E . (1974) . S tud i es o f c losed mar ine cu l tu re sys t ems . Prog. Fish. Cult.,3 6 ( I ) , 8 - 1 5 .


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84 J. F. WickinsSpot te , S . (1979) . Seaw ater Aquarium s, the Capt ive Env ironm ent , Wiley Inter-sc ience , New Y ork , 413 pp .S t r ick land , J. D . H. & Parsons, T . R . (1968) . A p rac t ica l han dbo ok o f seawateranalysis . Bull . Fish. Res. B d C an., 167, 1-311.Tiews, K. (Ed.) (1981). Aqu acul ture in He ated Ef f luen ts and Recirculation System s,

Vols 1 an d 2, H ee ne m an n Verlagsgesellschaft, Berlin.Weyl , P . K. (1967) . The so lu t ion behav iour o f carbonate mater ia l s in seawater .

Stud. Trop. Oceanogr., 5, 178-228.W heaton , F . W. , Law son , T . B . & L om ax , K. M. (1979) . Fo am frac t iona t ion app lied

to aquacu l tu ra l sys tems . Proc. 10th A nn . M eeting Wld. Maricult. Soc., Honolulu,Hawai i, USA, 22 -26 January, Louis iana S ta te Univers i ty , pp . 79 5-808 .

Whi t f ie ld , M. (1974) . The ion-assoc ia t ion model and the buffer capac i ty o f thecarbon d iox ide sys tem in seawater a t 25C and 1 a tmosph ere to ta l p ressure.Limnol. Oeeanogr., 1 9 , 2 3 5 - 4 8 .

Wickins , J . F. (1981). Water qual i ty requirements for in tensive aquacul ture: areview. In: Aqu acul ture in Hea ted Ef f luen ts and Recireulation System s, Vol. 1 ,ed. K. Tiews, He en em an n Verlagsgesellschaft, Berlin, pp. 1 7-37 .

Wickins , J . F . (1982) Op por tun i t i es fo r fa rm ing Crus taceans in wes te rn tem pera teregions. In: Recen t Advanees in Aquacu l ture , eds J . F. Muir and R. J . Roberts ,C ro o m He lm , L o n d o n , p p . 8 7 -1 7 7 .

Wickins , J . F. (1983). Studies on marine biological f i l ters : model f i l ters . War. Res.,17 , 1769-80 .

Wickins , J . F . (1985) . A m m onia p ro duc t ion and o x ida t ion dur ing the cu ltu re o fmar ine p rawns and lobs te rs in l abora to ry rec i rcu la t ion sys tems . Aquacul turalEngineering, 4 (in press).

Wickins , J. F . & B eard, T . W. (1978). M inis t ry of Agricul ture, Fisheries and Fo od ,Prawn C ul tu re R esearch , Lab . Leaf l . , M AF F D irec t. F i sh . Res. , Low es to f t (42) ,41 pp.

Wickins , J . F. & Helm, M. M. (1981). Seawater t reatment . In : A q u a r i u m S ys t em s ,ed . A. D. Hawkins , Acad emic Press, Lo ndo n , pp . 63-128 .

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