Poxton 1982 Aquacultural-Engineering

7/28/2019 Poxton 1982 Aquacultural-Engineering

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Aquacultur al Engineeri ng 1 ( 1 9 8 2 ) 1 5 3 - 1 9 1

W A T E R Q U A L I T Y C R I T E R I A F O R M A R I N E F I S H E R IE S

M . G . P O X T O N a n d S . B . A L L O U S EAquaculture Engineering Group, Heriot-Watt University, Chambers Street,Edinburgh EH1 1HX, Seotland, UK

ABSTRACTThis paper provides a summary o f information on sea water for those engineers whohave little experience of water quality but f ind themselves interested or involved withmariculture. As well as considering the natural environment, changes which occur onremoval o f sea water to a land-based facili ty are included. In order that the designengineer can appreciate the importance of maintaining water quality, environmentalfactors affecting fish are consMered in sufficient detail for most of the problems tobecome apparent. Reference is made to freshwater fish where appropriate and whereexamples of marine species are lacking. It is to be hoped that a great deal o f new workwill be forthcoming in the area of water quality criteria for mariculture in the nearfuture. This paper will serve to highlight many o f the areas still requiring researchbefore mariculture systems can be operated close to maximum efficiency. Until thisinformation becomes available, the only sensible course fo r engineers to take is todesign systems with maximum flexibility and considerable safely margins with respectto fish loading and production.

INTRODUCTIONAn important recent trend in aquaculture is that toward greater intensification withcontrol of environmental conditions. In many parts of the world, fish production ishandicapped either by climatic conditions or water availability. Such circumstanceshave promoted the development of water reconditioning and re-use systems, many ofwhich have been described by Kinne (1976) and Tiews (1981). In the design of suchsystems, great effort is made to ensure that the filtration capacity is adequate for t h efish production envisaged, in order to maintain the environmental conditions r e g a r d e das optimal for the species being cultured.

153Aquacultural Engineering 0144-8609/82/0001-0153/$02.75 Applied Science Publishers Ltd,England, 1982Printed in Great Britain


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1 5 4 M . G . P O X T O N , S . B . A L L O U S ES e v e ra l b o d i e s h a v e a s s e ss e d t h e r e l e v a n t l i t e r a tu r e t o d e v e lo p w a te r q u a l i t y c r i t e r i a

p a r t i c u l a r l y w i t h r e s pe c t t o f re s h w a t e r s . T h e A q u a t i c L i f e A d v i s o r y C o m m i t t e e( A L A C ) w i t h i ts s e ve ra l a t t a c h e d s m a l le r b o d i e s , t h e W a t e r R e s e a r c h C e n t r e ( U K ) , t h eE n v i r o n m e n t a l P r o t e c t i o n A g e n c y ( E P A ) a n d t h e E u r o p e a n I n l a n d Fi sh e ri es A d v i s o ryC o m m i s s i o n ( E I F A C ) , h a s p r o d u c e d a n i m p re s si ve l i t er a tu r e . T h e w o r k o f t h e E I F A C' W o r k i n g P a r t y o n W a t e r Q u a l i t y C r it e ri a f o r E u r o p e a n F r e s h w a t e r F i s h ' a n d t h er e p o r t s o f t h e ' W o r k i n g P a r t y o n T o x i c i t y T e s t i n g P r o c e d u r e s ' , t o g e t h e r w i t h ad d i-t i on a l i n f o r m a t i o n , h a s r e c e n t ly b e e n u p d a t e d b y A l a b a st e r a n d L l o y d ( 1 9 8 0 ) .

T h e a p p r o a c h t o w a t e r q u a l i t y c r it e ri a f o r m a r i n e f is h , a s a d o p t e d h e r e , h a s b e e nm a i n l y d e p e n d e n t o n s t u d i e s c o n d u c t e d o n f r e s h w a t e r a n d m i g r a t o r y f is h i n e s tu a r ie s ,d u e t o t h e r e s t r i c t e d a v a i l a b i li t y o f l i t e r a tu r e o n m a r in e f i sh e r ie s . N e v e r th e l e ss , it w a sf e lt t h a t i n f o r m a t i o n r e le v a n t t o m a r i n e f i sh f a r m i n g o u g h t t o be r e v ie w e d in a f o r m a tr e l e v a n t t o t h o s e e n g in e e r s n o w in v o lv e d i n s y s t e m d e s ig n . F o r a c o m p r e h e n s iv et r e a t m e n t o f li t e r at u r e o n t h e c u l t u r e o f m a r i n e o r g a n i s m s , r e fe r e n c e s h o u l d b e m a d et o B a r d a c h e t a l. ( 1 9 7 2 ) , K i n n e ( 1 9 7 6 ) , P i l l a y a n d D i l l ( 1 9 7 9 ) a n d T i e w s ( 1 9 8 1 ) .

T H E C O M P O S IT I O N O F N A T U R A L S E A W A T E R

A l t h o u g h w a t e r is d e f i n e d c h e m i c a l l y a s H 2 0 , a ll n a t u r a l w a t e rs c o n t a i n v a r y i n ga m o u n t s o f d i f f e r e n t m a t e r ia l s. A s a u n i v e rs a l so l v e n t, w a t e r c o n s i s ts s im p l y o f a l m o s te v e r y s u b s t a n c e w h i c h h a p p e n s t o c o m e i n t o c o n t a c t w i t h i t. M o r e o v e r , o n e m a yp o s t u l a t e t h a t t r a c e s o f all k n o w n n a t u r a l e l e m e n t s o c c u r in s ea w a t e r ( K a l le , 1 9 7 1 ) .

N i n e e l e m e n t s w h i c h c o n s t i t u t e m o r e t h a n 9 9 % o f n a tu r a l s ea s al ts a re v i r tu a l lyc o n s t a n t ( A t z , 1 9 6 4 ; W i ls o n , 1 9 7 5 ) . A l t h o u g h t h is m a y b e a r e a s o n a b le a p p r o a c ht o w a r d t h e s t u d y o f t h e m a j o r c o n s t i t u e n t s ( T a b l e 1 ), it d o e s n o t g iv e a c o m p l e t ep i c t u r e o f t h e c h e m i c a l c o m p o s i t i o n o f se a w a t e r . T h e g r e a t n u m b e r o f m i n o re l e m e n t s , d i s s o lv e d ga s es a n d o r g a n i c m a t t e r w h ic h a r e p r e s e n t i n se a w a t e r , e i t h e r a sa n io n s , c a t i o n s o r m o le c u l e s , a l l i n d y n a m ic e q u i l i b r i u m , h a s l e d t o d i f f i c u lt i e s i ns tu d y in g i ts c h e m ic a l c o m p o s i t i o n . A s a l if e s u p p o r t e r , n a tu r a l s e a w a t e r is a h ig h lyc o m p l e x s y s t e m . S o m e o f i ts c o n s t i t u e n t s s u c h as c a r b o n , n i t ro g e n , p h o s p h o r u s a n ds i l ic o n a r e i n v o lv e d i n b io c h e m ic a l c y c l e s . W h e n a v o lu m e o f s e a w a t e r w a s a l l o w e d t oe v a p o r a t e t o d r y n e s s a n d t h e n r e c o n s t i t u t e d w i t h f r e s h w a t e r , i t w a s f o u n d t h a t i tw o u ld n o t s u s t a in l i fe a s i t o r i g in a l ly d id ( A tz , 1 9 6 4 ) . T h i s is p r e s u m a b ly d u e t o t h el a c k o f l i f e -s u p p o r t i n g m i c r o - o r g a n is m s w h i c h t e n d t o b a la n c e a n d r e c o n d i t i o n n a t u r a lsea wa te rs .S a l i n it y a n d t h e m a / o r e l e m e n t s

S a l in i t y i s d e f i n e d a s t h e w e ig h t o f t h e d i s s o lv e d s u b s t a n c e s w h ic h is l e f t f r o m 1 k go f se a w a t e r a f t e r t h e c o m p l e t e o x i d a t i o n o f o r g a n i c m a t t e r , c o m p l e t e r e p l a c e m e n t o fc a r b o n a t e s b y a n eq u i v a l e n t q u a n t i t y o f o x i d e s a n d t h e r e p l a c e m e n t o f b r o m i d e a n di o d i d e b y a n e q u i v a l e n t a m o u n t o f c h l o r id e . A c c o r d i n g l y , it w o u l d a p p e a r t h a t a


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WATER QUALITY CRITERIA FOR MARINE FISHERIES 155TABLE 1The major elements of 35%0 salinity sea water (after I(alle, 1971)

E l e m e n t s g k g - ~ b M i l l i- e q u iv a l e nt k g -C a t ionsSodium 10.752 467.56Potassium 0.375 10.10Magnesium 1.295 106.50Calcium 0.416 20.76Strontium 0.008 0.18

605.10A n i o n sChlorine 19. 345 545.59Bromine 0.066 0.83Fluorine 0.0013 0.07Sulphate 2.701 56.23aBicarbonate 0.145 -Boric acid 0.027 -

602.72Surplus of cations over strong anions(Alkalinity) : 2.38

a Bicarbonate and carbonate will vary according to the pH of thesea water.b Milli-equivalentkg -~ = g kg ~ ionic charge 1000.atomic weight of ion

certain empirical relationship must exist between salinity and chlorinity. The latteris defined as the chlorine equivalent of the total halide conce ntra tion and the relation-ship given by UNESCO (1962) has the expression:

S%o = 1.80655 O % (1)The largest relative variations in the compos iti on of sea salt occur in the calcium andcarbonate contents due to biological processes (Kalle, 1971). The salinity range inopen oceans is rather small and lies bet ween 33 and 37/0o S with a mean of nearly35/ooS (Nicol, 1967). In sea water, however, the breadth of fluctu atio n extendsbetween 0%o and 41%o S at the surface (Kalle, 1971). The amount of river inflowand the extent of evaporation as well as the quantity of rain are the usual causes ofthis considerable variation. The salinity ranges for intermediate and deep waters areless than those at t he surface. Values for deep waters generally lie between 34.5 %0and 35% oS, though exceptions are not uncommon (Nicol, 1967). In open oceans,salinity fluctuations are small because they are distributed over wide areas and havescarcely any biological significance. Nevertheless, salinity may fluctuate above orbelow the me an to such an extent that the tolerance limits of many aquatic organismsare exceeded.


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156 M . G . P O X T O N , S . B . A L L O U S E

F r o m th e p h y s io lo g i c a l a n d e c o lo g i c a l p o in t o f v i e w , th e s i g n i f i c a n c e o f s a l i n it yl ie s i n t h e o s m o t i c p r e s s u r e w h ic h i t p r o d u c e s . S a l i n i t y is a n im p o r t a n t f a c t o r in t h es u rv i va l, g r o w t h a n d d i s t r i b u t i o n o f m a n y f is h ( H o l l i d a y , 1 9 6 5 ) . M o s t o f t h e w o r kw h i c h h a s b e e n d o n e i n t h is r e s p e c t f o c u s e d m a i n l y o n t h e e f fe c t o f s a l in i ty o n t h ed i f f e r e n t d e v e l o p m e n t a l s ta g es o f f is h f r o m e g g t o m e t a m o r p h o s i s . H o l l i d a y ( 1 9 7 1 )s t a t e d t h a t i t w a s d i f f i c u l t t o g e n e r a l i se a b o u t t h e s u r v iv a l o f a d u l t f i s h i n d i f f e r e n ts a l in i ti e s. S o m e s p e c i e s o f f i s h, d u r in g t h e i r a d u l t l i fe , c a n t o l e r a t e b o th c o m p le t e lyf r e sh a n d m a r i n e w a t e r s , t h e m a j o r i t y a r e r e st r i ct e d t o o n e o r t h e o t h e r e n v i r o n m e n t .

T h e r e s p o n s e o f a s p e c i e s o f f i s h t o a d e f in e d l e v e l o f s a l i n i ty d i f f e r s w i th v a r io u sl if e s ta g e s . A f t e r h a t c h in g , t il e l ar v a e o f b o th h e r r i n g (Clupea harengus) ( H o l l i d a y a n dBla x t e r , 1 9 6 0 ) a n d p la i c e (Pleuronectes platessa) ( H o l l i d a y , 1 9 6 5 ) p o s s e s s a t e m p o r a r ya b i l i t y t o s u r v ive a w id e r a n g e o f s a l in i t ie s w h ic h h a s n o t b e e n f o u n d i n t h e a d u l t s .

T h e e f f e c t o f v a r i o u s sa l in i t ie s ( 1 0 , 2 0 , 3 0 , 4 0 a n d 5 0 /o o S ) o n t h e d e v e lo p m e n t a n ds u r v iv a l o f D o v e r s o l e (Solea solea) e g gs h a s b e e n e x a m i n e d b y F o n d s ( 1 9 7 9 ) . T h e e gg sa n d l a rv a e f l o a t e d i n s a li n it ie s g r e a t e r t h a n 3 0% o S , w h e r e a s b e lo w 3 0 /0 o S th e y sa n kw i th r e s u l t a n t m o r t a l i t y d u e t o c r o w d in g . W i th t hi s e x c e p t i o n , s u r v iv a l i n s a l in i ti e s o f20 , 30 and 40 /ooS w as s imi la r , wh i le a t 10 and 50 /ooS , egg su rv ival was c lea r lyr e d u c e d a n d t h o s e l a r v a e w h i c h w e r e p r o d u c e d w e r e a b n o r m a l .

A c o n s i d e r a b l e a m o u n t o f e x p e r i m e n t a l e v i d e n ce i n d i c a t e s t h a t g r o w t h o f f is h ise n h a n c e d u n d e r m a r i n e c o n d i t i o n s . B o t h f o o d i n ta k e a n d c o n v e r s i o n e f f i c i e n c y w e r ef o u n d t o b e i n c r e a s e d w i t h s a l in i ty ( K i n n e , 1 9 6 0 ) .

S a l i n it y c h a n g e s m a y a f f e c t t h e b e h a v i o u r o f f is h i n d i f f e r e n t w a y s . T h e y m a ya l t e r t h e a c t i v i t y l ev e l, o r c a u s e a v o id a n c e o r p r e f e r e n c e r e s p o n s e s . A l th o u g h t h ep e r t i n e n t l i t e r a tu r e is v e r y l im i t e d , i t a p p e a r s t h a t t h e c r u i s in g s p e e d o f f i s h isd e p r e s s ed w i t h s a l i n it y ( H o l l i d a y 1 9 7 1 ) . T h i s w a s a t t r i b u t e d t o t h e o s m o t i c c h an g e sin t h e f i s h .

M inor e lementsE l e m e n t s w h i c h o n l y e x i s t a t s m a ll c o n c e n t r a t i o n s i n s ea w a t e r a r e u s u a l ly r e f e rr e d

t o a s m i n o r o r t ra c e e l e m e n t s . T h e t e r m ' m i n o r ' is u s e d t o e x p re s s th e q u a n t i t y n o t t h ei m p o r t a n c e o f t h e s e e l e m e n t s f o r , in s p i te o f t h e i r lo w c o n c e n t r a t i o n s , t h e y a re es se n -t ia l f o r t h e c o n t i n u e d e x i s t e n c e o f a q u a t i c l i fe , e i t h e r a s n u t r i e n t s u b s t a n c e s f o r g r o w t h( p h o s p h a t e s a n d n i t r o g e n - c o n t a i n i n g s u b s t a n c e s ) o r b e c a u s e t h e y e n t e r i n t o t h e c o m -p o s i t io n o f t h e a n i m a l b o d y ( i r on , c o p p e r a n d p h o s p h o r u s ) .

T h e r e a r e a b o u t 6 1 m i n o r e l e m e n t s i n t h e c o m p o s i t i o n o f s ea w a t e r ( K a l le , 1 9 7 1 ) ,s o m e o f w h i c h a r e li s te d i n T a b l e 2 . I n c o n t r a s t t o t h e m a j o r c o m p o n e n t s , t ra c ee l e m e n t s o f s e a w a t e r c a n s h o w v e r y m a r k e d f l u c t u a t i o n s d u e t o t h e i r c o n t r i b u t i o n t ob io lo g i c a l p r o c e s s e s . T h i s is e s p e c ia l l y t r u e f o r p h o s p h o r u s a n d n i t r o g e n ( K a l le , 1 9 7 1 ) .A v a r i a ti o n o f a n o r d e r o f m a g n i t u d e i n t h e c o n c e n t r a t i o n s o f m i n o r e l e m e n ts m a yo c c u r o n l y u n d e r e x t r e m e c o n d i t i o n s ( B r e w e r , 1 97 5 ) . H o w e v e r , a n y c h a n ge in t hec o n c e n t r a t i o n o f m i n o r e l e m e n t s i s c o n s i d e r e d s i g n if i ca n t i n it s e f f e c t o n a q u a t i c l i fe .


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WATER QUALITY CRITERIA FOR MARINE FISHERIESTABLE 2Some minor e l emen t s o f 19% 0 ch lo r in ity seawater (after Nicol, 1967)

Element mg kg-Boron 5 -0Silicon 0.01-7-0Nit rogen 0 .001-0.7Phosphorus 0 .001-0.17Iron 0-001-0-29Manganese 0.001-0.01Copper 0 .01 -0 -024Zinc 0 .005-0-014Molybdenum 0 .0003-0 .016Vanadium 0.0002-0.007Chromium 0 .001-0 .003Cobal t 0 .0001-0.0005

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pH, a lkal in i t y and buf fer ing ac t iv i t yS e a w a t e r i s a l k a l i n e a s a c o n s e q u e n c e o f a s u r p l u s o f c a t i o n s o v e r a n i o n s ( T a b l e 1 ).

I n g e n e r a l , p H v a l u e f a l ls i n t h e r a n g e 7 . 5 - 8 . 4 , a l t h o u g h v a l u e s a b o v e o r b e l o w t h e s el i m i t s ar e n o t u n c o m m o n . N o r m a l l y , t h e p H i s a t it s m a x i m u m w i t h i n t h e s u rf a c e1 00 m , f a ll in g t o a m i n i m u m w i t h a d e p t h o f 2 0 0 - 1 2 0 0 m . D e e p e r s t il l, t h e p H r i se s t oa d e e p s e a m a x i m u m ( P e r k i n s, 1 9 7 4 ) . E a r l ie r s t u d i e s on t h e r e l a t i o n s h i p b e t w e e n p Ha n d d e p t h s u g g e s t e d t h a t t h e r e w a s a lw a y s a n o t i c e a b l e , t h o u g h n o t v e r y g r e at , d i m i n u -t i o n f r o m t h e s u r f a c e d o w n w a r d s b u t t h e m i n i m u m v a lu e s w e r e n o t u s u a l l y a t t h eb o t t o m ( A t k i n s , 1 9 2 2 ). T h e l o w e r p H v a l u e s o b s e r v e d in d e e p w a t e r s a re p r o b a b l y d u et o b i o l o g i c a l p r o c e s s e s , w h e r e a s h i g h e r v a l u e s i n d e e p e r la y e r s c a n b e d u e t o th e e f f e c to f h y d r o s t a t i c p r e s s u r e o n t h e d i s s o c i a t io n c o n s t a n t o f c a r b o n i c a c i d . S e a w a t e r a t h i g hp r e s s u re c a n d i s s o l v e s u b s t a n t i a l l y m o r e c a l c i u m c a r b o n a t e t h a n s u r fa c e w a t e r( P e r k i n s , 1 9 7 4 ) .

S e a w a t e r s , i n g e n e r a l , re s i s t c h a n g e i n t h e i r p H v a l u e s. I n f r e s h o r p u r e w a t e r s t h ea m o u n t o f c a r b o n d i o x i d e a d d e d o r r e m o v e d d u r in g p l a n t g r o w t h w o u l d h a v e a m o r ed r a m a t i c e f f e c t o n p H t h a n i n s e a w a t e r . T h i s i s d u e t o t h e a l k a l i n i t y o f s e a w a t e rw h i c h p r o v i d e s g r e a t e r p r o t e c t i o n a g a i ns t h i g h c a r b o n d i o x i d e b u i l d - u p .

T h e c a p a c i t y o f t h e w a t e r t o a c c e p t p r o t o n s is k n o w n a s t h e a l k a l i n i t y , w h i c h isd e f i n e d a s t h e n u m b e r o f m i l l i- e q u i v a l e n ts o f h y d r o g e n i o n s w h i c h a r e n e u t r a l i s e d b y1 k g o f s e a w a t e r w h e n a n e x c e s s o f a c i d is a d d e d ( S t r i c k l a n d a n d P a r s o n s, 1 9 6 8 ). T h em i l l i - e q u i v a l e n t a m o u n t s o f c a t i o n s a n d a n i o n s i n s e a w a t e r a r e n o t b a l a n c e d a g a i n s te a c h o t h e r ; t h e c a t i o n s e x c e e d t h e a n i o n s b y 2 - 38 m i l l i- e q u i v a l e n t s ( T a b l e 1 ) w h i c hr e s u l t s i n s e a w a t e r b e i n g s l i g h t l y a l k a l i n e a n d s h o w i n g a s t r o n g b u f f e r i n g c a p a c i t y( K a l l e , 1 9 7 1 ) .

T h e a l k a l i n i t y o f s ea w a t e r i s d u e m a i n l y t o t h e p r e se n c e o f t w o c o m p l i c a t e ds y s t em s , k n o w n a s t h e c a r b o n a t e a n d b o r a t e s y s te m s . W h e n t h e a m o u n t o f h y d r o g e n


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1 5 8 M . G . P O X T O N , S . B . A L L O U S E

ion (milli-equivalent kg ~) needed to convert all the anions of the weak acids to theirunionised acids is known, then the term 'tota l alkalinity', A, is applied to that amount(Skirrow, 1975):

A = [HCO3] + 2[CO3] + [B(OH)4] (2)Carbonate alkalinity, however, contributes only to the alkalinity made by thebicarbonate and carbonate species. The borate cont ribut ion to alkalinity arises fromthe ionisation of boric acid:

H3BO3+ H20 = B(OH)] + H + (3)The B(OH)4 contribution to total alkalinity can be obtained by subtracting the

carbonate contribution from the measured total alkalinity. The borate system, at thenormal pH of sea water, is not as important as the carbonate system (Perkins, 1974).

The carbonate system in sea water follows certain steps, each of which ischaracterised by an equilibrium constant (Skirrow, 1975):

C O 2 ( g ) ~-~ C O 2 ( a q )H 2 0 + C O 2 (a q) ~ H 2 C O 3

H2CO 3 ~ H + + HCO~H C O ; .~ n + + c o ~ -

( 4 )( 5 )(6 )( 7 )

The percentage proportion of each species of the carbonate system (free carbondioxide, bicarbonates and carbonate) depends on the hydrogen ion concentration ofthe water and, conversely, a change in these values will affect the pH. Below pH 4-0,only free carbon dioxide occurs in sea water of 35/oo S. At pH 7.5, the percentageof bicarbonate reaches its maximum, whereas at higher pH values bicarbonate isincreasingly replaced by carbonate ions (Kalle, 1971). Hence, at the normal pH rangeof sea water, the bicarbonate is the most dominant species of the carbonate systena(about 80%); the remainder is free carbon dioxide near the lower end of the pH rangeand carbonate ion near the upper end (Home, 1969).

Natural temperature regimes in the seaThe range of temperatures encountered in the sea is small in comparison with thatobserved on the land surface (Nicol, 1967; Kinne, 1963). Temperature in the open

ocean ranges from about --2 to 30C and that of sea and brackish water from about- 2 to 43C (Kinne, 1963). The narrower temperature range of oceanic water resultsfrom the steady system of oceanic circulation and the high specific heat of water(Nicol, 1967).

Sea water temperatures fluctuate due to diurnal and seasonal variations and alsochange with latitude and longitude. The annual and latitudinal range throughout alltemperate and sub-tropical seas lies between 0-28C, while in the open ocean the


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WATER QUALIFY CRITERIA FOR MARINE F ISHERIES 159annua l va r i a t i on i s no t more t han 10 C a t any p l ace (N ico l , 1967 ) . Su r f ace t empe ra -t u r e s a r e sub j ec t t o t he se va r i a t i ons and i t was found t ha t w i th i nc r ea s ing dep th no ton ly does t he t em pe ra tu r e d rop bu t s ea sona l va r i a t ions d i s appea r be low dep ths o f200 m (Nico l , 1967 ) . T he ave rage dai l y su r f ace t em pe r a tu r e va r i a ti on in oceans andseas is abo u t 0 .2 -0 .3 C (K inne , 1963 ) . How eve r , unde r e x t r em e cond i t i ons , d iu rna lt em pe ra tu r e v a r i a t ions in t he up pe r w a t e r l aye r may r each 3C (Wi lli ams , 1962 ) .

Dissoh, ed gasesIn sea water t i l e d i sso lved gases which a re of par t icu la r b io logica l and ecologica l

imp or t an ce a r e ox ygen and ca rbon d iox ide . These ga se s e i t he r o ri g ina t e f r om theva r ious li fe p roces se s o r a r e d i s so lved f rom the a tm osph e re a t t he su r f ace . Gase sdisso lve acco rd ing to tem pe ra tu re , sa l in i ty and the ind iv idua l gas par t ia l p ressureg rad i en t s be tween t he a tmo sphe re and t he u ppe r l aye r o f the s ea wa t e r .

Oxygen. Natu ra l s ea w a t e r bod i e s show a l arge va r ia t i on (0 -1 2m gl i t r e - 1 ) i nd i s so lved oxyg en con t e n t , bo th geo g raph i ca l l y and s ea sona l l y (N ico l , 1967 ) . V a r i a t ionsr e su lt f r o m p ho to syn the t i c a c t iv i t ie s , as wel l as f r om the f r ee exchange w i th t hea tm osph e re . Su r f ace l aye r s, in gene ra l, con t a in h igh oxyg en leve ls due t o f r ee exchangew i t h t h e a t m o s p h e r e w h e r e a s d e e p w a t e rs , w h i c h o b t a i n t h e ir o x y g e n t h r o u g h m i x i n gand wind ac t i on (N ico l , 1967 ) , a r e o f t en l ow in oxygen . I n add i t i on t o t he r educeda t m o s p h e r i c e x c h a n g e , d e e p m a r i n e w a t e rs h a v e l o w e r p h o t o s y n t h e t i c a c t iv i t y a n dreach a cond i t i on whe re r e sp i r a t ion ex ceeds pho to syn the s i s (Dav i s, 1975 ). Deepe rwa te r masse s de r i ve t he i r oxygen o r i g ina l l y f r om the a tmosphe re p r i o r t o submergence ,and t h i s i s dep l e t ed by t he oxyg en dem ands o f l iv ing o rgan isms and dead o rgan i cm a t t e r .

Da i l y f l uc tua t i ons i n d i s solved oxyg en con t en t c an be ve ry l a rge . Ta rzwe l l andCauf in (1953 ) f ound a l oca t i on i n a sou the rn Oh io c r eek wh ich was po l l u t ed w i thsewage and con t a ine d 19 .4 m g O5 l it r e -1 one a f t e rn oon and 0 -7 mg 02 l i tr e -1 t he n ex tm o r n i n g . D i s s o l v e d o x y g e n c o n t e n t f l u c t u a t e s i n r e s p o n s e t o t h e p h o t o s y n t h e t i c a n dre sp i r a to ry ac t i v i t i e s o f aqua t i c p l an t s . Eu t roph i c wa t e r bod i e s may f ace dange rousoxyg en dep l e t i on du r ing t he n igh t . Neve r the l e s s , com ple t e deo xyg ena t i o n on ly occu r sin i so l a ted a r ea s w i th poo r c i r cu l a t i on o r unusua l l y h igh r a t e s o f oxygen u t i l is a t i on(Vernbe rg , 1972 ) .

Seasona l l y , l ow l eve l s o f d i s so lved oxygen may occu r i n w in t e r due t o o rgan i cm a t t e r d e c a y u n d e r i ce co v e r w i t h o u t r e p l e n i sh m e n t o f o x y g e n f r o m t h e a t m o s p h e r e(Dav i s, 1975 ) . H igh t em pe ra tu r e s , on t he o th e r hand , r educe oxygen so lub i li t y i nw a t e r a n d i n cr e as e t h e o x y g e n d e m a n d b y a n i m a l r e s p ir a t io n .

A t t he su r f ace o f t he open oceans , t he oxy gen s a tu r a t i on va lue m ay r each 100%and gene ra l l y va r ie s on ly sl i gh tl y , a l t houg h up t o 120% sa tu r a t i on is no t un co m m onin h igh ly p rodu c t i ve a r ea s du r ing l ong sunny days (Ka l le , 1972a ) .


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160 M.G. POXTON, S. B. ALLOUSE

Carbon dioxide. F r e e c a r b o n d i o x id e is a h i gh l y s o lu b l e c o m p o u n d ( E q n 4 - 7 )p r e s e n t i n a c o m p l e x c y c l ic s y s t e m o f w h i c h n o t a l l a s p e c t s a r e f u l l y u n d e r s t o o d( S k i r r o w , 1 9 7 5 ) . T h e p H o f t h e w a t e r , a s d i s cu s s e d e a rl ie r , a f f e c t s t h e q u a n t i t y o f f r e ec a r b o n d i o x i d e p r e s e n t i n s o l u t i o n , a s d o e s t e m p e r a t u r e a n d s a l in i t y .

I n a d d i t i o n t o t h e i n te n s i v e c h e m i c a l t r a n s f o r m a t i o n s o f c a r b o n d i o x i d e i n s e aw a t e r , i t i s i n v o l v e d i n t h e m e t a b o l i s m o f m a r i n e o r g a n i s m s . P h o t o s y n t h e t i c p l a n t sm u s t e x c h a n g e o x y g e n f o r c a r b o n d i o x i d e in t h e l ig h t . S i m u l t a n e o u s l y , c a r b o n d i o x i d ei s b e i n g e x c h a n g e d f o r o x y g e n b y m a r i n e o r g a n i s m s . I n t h e d a r k , t h e f i rs t p r o c e s sc e a s es , r e s u l ti n g in f l u c t u a t i o n s i n b o t h o x y g e n a n d c a r b o n d i o x i d e c o n t e n t s i n s eaw a t e r . G e n e r a l l y , t h e r a ti o o f g a s e x c h a n g e v ia p h o t o s y n t h e s i s a m o u n t s t o o n e o x y g e nm o l e c u l e p r o d u c e d t o e a c h c a r b o n d i o x i d e m o l e c u l e c o n s u m e d ( i. e . O 2 / C O 2 = 1 ) ; f o ro x i d a t i v e m e t a b o l i s m t h e r e v e rs e is t r u e ( V i d a v e r , 1 9 7 2 ) .

T h e v a r i a t i o n i n fr e e c a r b o n d i o x i d e c o n t e n t i n s e a w a t e r h a s b e e n r e p o r t e d t o fa lli n t h e r a n g e o f 6 7 - 1 1 1 m g l i tr e -~ ( N i c o l , 1 9 6 7 ) .Organic substances

O r g a n i c s u b s t a n c e s i n s e a w a t e r c o m e f r o m s e v er a l s o u r c e s i n c lu d i n g e x c r e t i o n b yl iv i n g m a r i n e o r g a n i s m s , d e g r a d a t i o n o f d e a d o r g a n i s m s a n d f r o m l a n d r u n o f f .O p e r a t i o n a l l y , t h e s o u r c e o f o r g a n i c m a t t e r is n e i t h e r c r i t ic a l n o r l i m i t e d . A s l o n g a st h e r e i s p h o t o s y n t h e t i c a c t i v i ty , c a r b o n is f i x e d i n o r g a n i c m a t t e r ; i t is t h e n r e le a s e da g a in t o t h e e n v i r o n m e n t a s a b y p r o d u c t e i t h e r d u r i n g l if e o r a f t e r th e d e a t h o f th eo r g a n i s m .

D u r i n g p e r i o d s o f g r o w t h , m o s t p h y t o p l a n k t o n s p e c i es r e le a se r e l a ti v e ly m i n o ra m o u n t s o f th e c a r b o n w h i c h t h e y f i x e d d u r in g p h o t o s y n t h e s i s . U n d e r s t re s s, h o w e v e r ,m u c h l a rg e r a m o u n t s a r e r e l e a se d , w h i l s t a f t e r d e a t h a n d d e g r a d a t i o n s t il l g r e a t e ra m o u n t s a r e r e l e a s e d . T h e o r g a n i c l n a t e r i a ls r e l e a s e d a re d i f f e r e n t i n e a c h o f th e s et h r e e c l as se s o f e v e n t s ( W a n g e r s k y , 1 9 7 8 ) . C a r b o h y d r a t e s , p e p t i d e s , f a t t y a c i d s, to x i n s ,a n t i - b a c t e r ia l m a t e r i a l s a n d v i t a m i n B 12 h a v e al l b e e n r e p o r t e d f r o m c u l t u r e s o f m a r i n ep h y t o p l a n k t o n . D e s p i te t h e p r e se n c e o f s u c h a v a r i e ty o f o r ga n ic c o m p o u n d s ,d i s so l v e d o r g a n i c c a r b o n ( D O C ) is o f t e n u s e d as a n a p p r o x i m a t i o n f o r d i s so l v e do r g a n i c m a t t e r ( D O M ) .

D O C d e c r e a s e s w i t h d e p t h ( M e n z e l , 1 9 6 4 ; W i l li a m s , 1 9 7 5 ; W a n g e r s k y , 1 9 7 8 ) , v a l u e sf o r t h e u p p e r 1 0 0 m b e i n g i n t h e r a n g e 0 . 6 - 1 . 0 m g c a r b o n l it re - t (W i l li a m s , t 9 7 5 ) ,w h i l st d e e p w a t e r v a l u es a r e a b o u t o n e - t h i r d l es s. A n n u a l l y , t h e D O M u n d e r g o e s s m a l lf l u c t u a t i o n s i n ti re s u r fa c e w a t e r a s a c o n s e q u e n c e o f p h y t o p l a n k t o n b l o o m s , b u t i nd e e p e r l a y e r s i t i s p r a c t i c a l ly c o n s t a n t ( K a l l e , 1 9 7 2 b ) . T h e l o s s o f D O M m a y o c c u r a s ar e s u lt o f c o n v e r s i o n i n t o p a r t i c u l a t e o r g a n i c c a r b o n , a d s o r p t i o n o n a ir b u b b l e s o r b yb i o l o g ic a l p r o c e s s e s s u c h a s d e c o m p o s i t i o n o r u t il i s a t i o n .

P a r t i c u l a t e o r g a n i c c a r b o n ( P O C ) in c l u d e s b o t h l i v in g ( e. g . p h y t o p l a n k t o n a n db a c t e r i a l a g g r e g a t e s ) , n o n - l i v i n g ( e g . d e t r i t u s ) a n d s u s p e n d e d p a r t i c l e s w h i c h a r e l a r g e ri n s iz e t h a n 0 . 5 - 1 . 0 m m d i a m e t e r ( P a r s o n s, 1 9 7 5 ) . D e t r i t a l P O C o f t e n e x c e e d s t h el iv i n g P O C , b u t t h e t o t a l P O C i s g e n e r a l l y o n l y a f r a c t i o n o f th e D O C .


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W A T E R Q U A L I T Y C R I T E R I A F O R M A R I N E F I S H E R I E S 161I n g e ne r a l, t h e q u a n t i t a t i v e r e l a t i o n s h i p b e t w e e n t h e c o n c e n t r a t i o n s o f o r g a n i c

m a t t e r i n s e d im e n t s , d i s s o lv e d i n se a wa t e r , s u s p e n d e d i n se a wa t e r a n d i n l iv in go r g a n i s m s i s a b o u t 1 0 0 0 : 1 0 0 : 1 0 : 1 ( Ka l l e , 1 9 7 2 b ) .

T H E C O M P O S I T I O N O F T H E W A T E R I N M A R I C U L T U R E S Y S T E M S

S e a w a t e r , w h e t h e r i n o p e n o r c l o s e d s y s t e m s , u n d e r g o e s s o m e b i o c h e m i c a l a l t e r a t i o n s .S o m e o f t h e s e o c c u r o n l y a f e w m i n u t e s a f t e r r e m o v a l w h i ls t o t h e r s o c c u r o n l y a ft e re x t e n d e d p e r i o d s o f o p e r a t i o n . S u c h c h a n g e s m a y b e c o u n t e r a c t e d b y v a r i ou s t r ea t -m e n t t e c h n i q u e s . A m o n g t h o se c o m m o n l y e m p l o y e d a r e m e c h a n i ca l , b i ol o g ic a l a n dp h y s i c o - c h e m i c a l w a t e r t r e a t m e n t s . T h e p r o c e s se s i n v o l v e d i n s o m e o f t h e s e t r e at -m e n t s a d d y e t a n o t h e r m a r g i n o f a l t e r a t i o n i n t h e c o m p o s i t i o n o f s e a w a t e r u n d e ro p e r a t i o n .C l o s e d s e a w a t e r s y s t e m s w e r e i n u s e m o r e t h a n a c e n t u r y a g o a n d t h e a d v a n t a g e so f s u c h s y s t e m s a r e w e ll r ec o g n i s e d . S o m e o f t h e se s y s t e m s h av e b e e n i n c o n t i n u o u so p e r a t i o n f o r v e r y l o n g p e r io d s o f t i m e : e x a m p l e s a r e t h e P l y m o u t h a q u a r i u m t a n k so f t h e M a r i ne B i o l og i c al A s s o c i a t i o n ( U K ) a n d t h e Z o o l o g i c a l S o c i e t y a q u a r i u m t a n k si n L o n d o n . S u c h o p e r a t i o n s e n c o u r a g e d i n v es t i g at o r s t o s t u d y t h e c h e m i c a lc o m p o s i t i o n o f th e s e a w a t e r t r e a t e d .C h a n g es o c c u r r i n g i n se a w a t e r a f t e r r e m o v a l f r o m t h e s e a

W h e n s e a w a t e r i s r e m o v e d f r o m t h e s e a , c h e m i c a l c h a n g e s c a n b e d e t e c t e d w i t h i n3 0 r a in o f s a m p l e c o l l e c t i o n . M i c r o - n u t ri e n t s a n d m a n y t r a c e e le m e n t s a r e p a r t i c u l a r lys u s c e p t ib l e t o r a p i d c h a n g e s i n c o n c e n t r a t i o n a s a r es u l t o f b i o l o g ic a l o r e n z y m a t i cp r o c e s s es ( R i l e y , 1 9 7 5 ) . F o r e x a m p l e , t h e c o n c e n t r a t i o n s o f a m m o n i a , n it r it e , n i t r at ea n d o r t h o p h o s p h a t e m a y c h a n g e s i g n i f i ca n t l y w i t h i n a n h o u r o f c o l l e c t i o n a s a r e s ul to f b i o t i c a c t i v i t y ( A t z , 1 9 6 4 ) . T h e r a p i d d e a t h o f m o s t p r o t o z o a n s a n d i n v e r te b r a t e sc a u s es a n i n c re a s e i n t h e a m o u n t o f o r g a n i c m a t t e r i n th e w a t e r ; a s i t u a t i o n w h i c hs u b s e q u e n t l y r e s ul ts i n a n i n cr e a se i n t h e b a c t e r i al p o p u l a t i o n ( K i n n e , 1 9 7 6 ) . T h e s eb a c t e r i a c a n r e d u c e t h e a m o u n t o f d i s so l v e d o x y g e n ; i n cr e a se c a r b o n d i o x i d e a n dt h e r e f o r e c a u s e p H c h a n g e s ; a n d , u n d e r a n a e r o b i c c o n d i t i o n s , p r o d u c e m e t h a n e a n dh y d r o g e n s u l p h i d e ( A t z , 1 9 6 4 ) . T h e l a tt e r i s v e r y t o x i c t o f i sh ( D o u d o r o f f a n d K a t z ,1950).

T h e d i s so l v e d o x y g e n c o n c e n t r a t i o n c a n a ls o c h a n g e a s a r e s u lt o f p h o t o s y n t h e s i sa n d s i m p l e t e m p e r a t u r e c h a n g e s .

T h e n a t u r e o f s t o ra g e c o n t a i n e r s o r t a n k s is a l so e x t r e m e l y i m p o r t a n t . F o r e x a m p l e ,s o f t g la ss m a y l e a c h s u f f i c i e n t al k al i t o a f f e c t c o n d u c t i v i t y m e a s u r e m e n t s w h i l s tp o l y e t h y l e n e is p e r m e a b l e t o g a se s. L o s s o f t r a c e e l e m e n t s a n d p h o s p h o r u s m a y o c c u rr a p i d l y a s a r e s u lt o f a d s o r p t i o n o n t o t h e w a ll s o f t h e s t o r a g e t a n k s .

P r o l o n g e d s t o r a g e c a n i m p r o v e t h e q u a l i t y o f s ea w a t e r s o a s t o s u p p o r t a q u a t i cl if e . T h e n u m b e r o f b a c t e r i a i s a f u n c t i o n o f s t o r a g e t i m e a n d t e m p e r a t u r e . I t h a s b e e n


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162 M. G. POXTON, S. B. ALLOUSE

reported that after storage of sea water for four years at 2-4C, bacterial life wasrestored, whilst at room temperature it became sterile in six months (Atz, 1964).

Rapid methods, widely used to stabilise bacterial population dynamics, involvesterilisation using either ozonation or ultra-violet radiation.

Chemical composition o f closed sea water syste msSea water which has been kept in recirculating systems for several months or years

undergoes changes in its composition. Materials added to the water by managementtechniques and treatment processes and not removed during treatment tend toaccumulate. Fish food and the products of fish metabolism, as well as the salts in thefresh water added to replace evaporation, all contribute to these changes. Phosphate,for example, is accumulated in recirculating systems due to feeding with proteins andis not removed by most of the known treatment processes except when an algal bedis used. Nitrates, however, accumulate by biological filtration due to nitrificationprocesses.

The chemical constituents of the water indicate the balance between the con-tamination from fish excretion and the purification processes taking place in thetreatment units. The aeration techniques and the period of cultivation also contributeto changes in the chemical composition and properties of sea water in mariculturesystems.

Saeki (1962) determined the major ions in four recirculating sea water aquaria.Table 3 shows that calcium and potassium were present in higher amounts andmagnesium in lower amounts than in natural sea water. Phosphate also increasedconsiderably while the alkalinity was greatly reduced. Comparable data have beenreported for the Zoological Society aquaria in London (Stowell, 1925; Oliver, 1957).

The increase in potassium is due mainly to fish excretion (Saeki, 1962), althoughsmall amounts may be contributed by the freshwater used to replace evaporatedculture water (Oliver, 1957). Neutralisation of low pH by the addition of lime can leadto a substantial increase in the amount of calcium present in aquarium water.Magnesium can decrease remarkably, especially in old sea water, by precipitation withphosphate; Saeki (1962) has shown that alkalinity reduction was a consequence ofcation (magnesium) decrease and anion (nitrate) increase. Phosphate increasedmarkedly only a short period after the operation of the recirculation techniquesstarted, then as time went on it began to precipitate with magnesium or calcium.Other inorganic constituents such as sodium and chloride did not change significantly.

Atkins (1922) found that the Plymouth aquarium tanks were usually at pH 7.6while the average of the open sea was pH 8.2. Lowering of the pH to levels belowneutrality has often been reported (Townsend, 1928; Oliver, 1957). In a relativelysmall volume of water, such as that in an aquarium containing a much larger numberof fish per unit volume than normally exists in the open sea, it is to be expected thatproducts of animal respiration and metabolism will disturb the pH equilibrium.Methods employed to maintain an adequate pH value in closed sea water systems


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Poxton 1982 Aquacultural-Engineering