neudecker 1982 aquacultural-engineering

7/28/2019 Neudecker 1982 Aquacultural-Engineering

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Aquaeul tural Engineeri ng 1 ( 1 9 8 2 ) 1 9 3 - 2 0 4

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

THOMAS NEUDECKERBundesforsehungsanstalt f i ir Fiseherei, Ins t i tu t f i ir Kiisten. und Binnenfiseherei ,D 2391 L angballigau, West Germany

A B S T R A C TT h e h y d r o g r a p h i c a n d c l i m a t i c s it u a t i o n a l o n g t h e G e r m a n c o a s t r e q u i r e s s p e c i a ll ya d a p t e d e q u i p m e n t f o r m a r i c u l t u r e e n te r p ri s es . T h e c o n t a i n e r s us e d in t h e p a s t f o r t h eo n - g r o w i n g o f o y s te r s ( C r a s s o s t r e a g i g a s T h u n b e r g ) i n s h a l l o w s e a a r ea s p r o v i d e dr e s ul ts w h i c h g a ve r e a so n f o r d e v e l o p i n g a n e w t y p e o f c o n t a i n e r w h i c h w a s t o b em o r e e c o n o m i c a n d p r o d u c e a h ig h q u a l i t y o y s t e r o f u n i f o r m s ha p e.

S m a l l p r o t o t y p e c o n t a i n e r s , b a s e d o n a g a l v a n i z e d ir o n c o n s t r u c t i o n , w e r e b u i l t a n dp l a c e d a t d i f f e r e n t s i t es al o n g t h e c o as t. T h e y h e l d 1 6 8 0 o y s t e r s, e a c h o f w h i c h w e r er e - a tt a c h ed w i t h c e m e n t o n t o s q u a re m e s h p la s t ic n e t ti n g w h i c h w a s s t a p le d o n o a kf r a m e s . O n t h e s e f r a m e s , w h i c h w e r e h a n d l e d l ik e d r aw e r s , th e o y s t e r s ha d o p t i m a lc o n d i t i o n s w h i c h w e r e b e l i ev e d t o b e b e t t e r t h an o n a n a t u r a l o y s t e r b ed . E a c h o y s t e rh a d i ts o w n s p a ce o f 7 c m b y 8 c m w i d e a n d 1 0 c m h i g h a n d w a s n o t h a n d l e d u n t i li t r e a c h e d m a r k e t s iz e . G o o d w a t e r e x c h a n g e w a s p r o v i d e d b y t h e o p e n c o n s t r u c t i o no f t h e c o n t a i n e r w h i c h a ls o g a v e p r o t e c t i o n a g a in s t p r e d a t o r s b y m e a n s o f a c o m p l e t em e s h c o v e r .

INTRODUCTIONM a r i c u lt u r e w i t h o y s t e r s is st il l o n a n e x p e r i m e n t a l l ev e l i n G e r m a n y . T h e t w o b a s i c a l lyd i f f e r e n t c o a s t l i n e s a t t h e N o r t h S e a a n d a t t h e B a l ti c S ea , w i t h s t r o n g t i d a l c u r r e n t sa n d s h a l l o w , f j o r d - l i k e w a t e r s , r e s p e c t i v e l y , b o t h w i t h t h e h a z a r d o f i c e i n w i n t e r ,r e q u i re s p e c i a l l y a d a p t e d e q u i p m e n t f o r t h e g r o w i n g o f o y s t e r s .

M e i x n e r ( 1 9 7 6 ) d e v e l o p e d a t y p e o f c o n t a i n e r f o r t h e t r a y c u l t i v a t i o n o f o y s t e r s ,w h i c h , w i t h m i n o r i m p r o v e m e n t s m a d e i n r e c e n t y e a r s , i s c u r r e n t l y in u s e .

* ~lhis art icle was presen ted as poster no. 111 at the W MS/EM S Aq uac ulture Congress at Venice.1 93Aquaeu ltural Engineering 0144-8609 /82[0001-0193 ]$02.75 Applied Science Publishers ktd,England, 1982

P r i n t e d i n G r e a t B r i t a i n


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194 THOMAS NEUDECKERT h e p r i n c ip l e o f g r o w i n g o y s t e r s i n c o n t a i n e r s i n G e r m a n y h a s p r o v e n t o b e v e r y

s a f e . R i s in g c o s t s o f t h e p l a s t i c t r a y s w h ic h a r e s t o c k e d i n s id e t h e s e g a lv a n i z e d i r o nc o n t a i n e r s , a s w e l l a s s il t a ti o n p r o b l e m s a n d r a t h e r v a r i a b le s h a p e o f p r o d u c e d o y s t e r s ,g a ve c a u s e t o l o o k f o r a n e w t y p e o f c o n t a i n e r w h i c h c o u l d b e as sa fe a n d a s e a s il yh a n d l e d b u t b e in g c h e a p e r a n d l e s s s u s c e p t i b l e t o s i l t a t i o n .

DEVELOPMENT AND DESIGNT o a v o i d b a d l y s h a p e d o y s t e r s a n d o b t a i n a m o r e u n i f o r m g r o w t h , o u r i d ea s f o l l o w e di m p r e s s io n s g iv e n b y s o m e p u b l i s h e d p h o t o g r a p h s a n d p e r s o n a l o b s e r v a t i o n s o f n a tu r a lo y s t e r b e d s a n d c u l t u r e g r o u n d s o f Crassostrea gigas i n o t h e r p a r t s o f t h e w o r l d( G a l t s o f f , 1 9 6 4 ; K o r r i n g a , 1 9 7 6 ; N e u d e c k e r , 1 9 8 0 ; N e u d e c k e r , 1 9 8 1 b ; Q u a y l e , 1 9 6 9 ) .H a l f - g r o w n o y s t e r s g e n e r a l ly s e e m t o g r o w u p w a r d a n d d o n o t n o r m a l l y g r o w a l o n gt h e s u b s t r a t e a n y m o r e . T h i s o b s e r v a t i o n w a s s u p p o r t e d b y a t e s t c o n d u c t e d i n 1 9 8 0w i t h 1 6 s p a t w h i c h w e r e a p p r o x i m a t e l y 3 0 t o 4 0 m m i n si ze , w h i c h w e r e re - a t t a c h e df l a t w i t h c e m e n t o n 4 m m N e t l o n m e s h a n d p l a c e d h o r i z o n t a l l y i n a t r ay . A l l o y s t e r sw h i c h s u r v iv e d h a d g r o w n a l m o s t u n i f o r m l y i n a n u p w a r d d i r e ct i o n ( a b o u t 4 0 t o 6 0 t o t h e h o r i z o n t a l ) a n d w e r e n i c e l y c u p p e d ( F i g . 1 ) .

A n a l y si s o f m o r p h o m e t r i c d a t a o f B a lt ic a n d N o r t h S e a o y s t e rs (C. gigas) gavei n d i c a t io n s o f t h e m a x i m u m s p a ce r e q u i r e d b y a 1 0 0 g m a r k e t o y s t e r i n G e r m a nw a t e r s ( N e u d e c k e r , 1 9 8 1 a ) . O n t h i s b as is , t h e s p a c e r e q u i r e d f o r o n e m a r k e t o y s t e rw a s c o n s i d e r e d t o b e 8 c m b y 7 c m w i d e a n d 1 0 c m h i g h .

T h e r e f o r e , o n e s q u a re m e t r e o f c o m m e r c i a l l y a v a il a bl e 2 0 m m p l a st ic n e t t i n g( D r C o e r s ( N e t l o n ) G m b H , A r t . - N o . 2 0 7 ) o f f e r e d s p a ce f o r 1 2 x 1 4 = 1 6 8 o y s t e r s

Fig. 1. Test conducted in 1980 with 16 re-attached oysters. They gre w almost uniformly and atan angle of approximately 50


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NEW OYSTER ON-GROWINGCONTAINER FOR MARICULTUREOPERATIONS 195(Fig. 2). As vertical growing of oysters is in common use, 10 layers of oysters,amo unt ing to a total of 1680 specimens, were placed in a prot otyp e cont aine r (Figs3 and 4). Fo r stability, each square metre sheet of netti ng was stapled to a frame ofoak boards fitting loosely into the U-shaped runners of the container (Fig. 6). Theconta iner itself was ma de out of U-shaped runners in such a way that the same framesused for the oysters could be used outside to prevent predation by crabs and sea-stars(Figs 4, 5, 6 and 7).

Fig. 2. One square metre of 20 mm plastic netting stapled to oak frames offers enough space for12X14 = 168 oysters.

Fig. 3. Two prototype containers are stacked with oysters in April 1981 at Langballigau, westernBaltic. The oak frames can be handled like drawers.


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1 9 6 T H O M A S N E U D E C K E R

F i g. 4 . T h i s p r o t o t y p e o f a n e w o y s t e r o n - g r o w i n g c o n t a in e r h o l d s 1 0 f r a m e s w i t h a t o t a l o f1 6 8 0 r e - a t ta c h e d o y s t e r s w h i c h a r e p r o t e c te d a g a in s t p r e d a to r s b y a c o m p l e t e m e s h c o v er .

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F i g. 5 . T o p v i e w o f p r o t o t y p e c o n t a i n e r ( d i m e n s i o n s i n m m ) .


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NEW OYSTER ON-GROW ING CONTAINER FOR MARICULTURE OPERATIONS 197

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- - ~ - - 2 - - ~ - -S i d e view of pro toty pe container (dimensions in ram).

H a l f - g r o w n o y s t e r s ( 3 0 t o 4 0 m m i n si z e) w e r e r e - a t t a c h e d w i t h o r d i n a r y b u i l d i n gc e m e n t u s i n g o n e la r g e t e a s p o o n f u l o f c e m e n t p e r o y s t e r ( F i g s 2, 8 a n d 9 ) . O n o n e h a l fo f t h e f r a m e , t h e o y s t e r s w e r e r e - a t t a c h e d f l a t , w h i l e o n t h e s e c o n d h a lf , a t a n a n gl eo f r o u g h l y 4 0 . In a ll , 1 0 o f t h es e c o n t a i n e r p r o t o t y p e s w e r e b u i l t a n d t e s t e d a t f iv ed i f f e r e n t s i te s , f o u r s it e s b e in g s i t u a t e d a lo n g t h e N o r th S e a c o a s t a n d o n e i n t h ew e s t e r n Ba l t i c .

RESULTST h e e x p e r i m e n t s a re s t il l u n d e r w a y a n d f in a l r e su l ts c o n c e r n i n g g r o w t h r a t es a n ds h a p e s o f t h e o y s t e r s w i l l b e a v a il a b le a t t h e e n d o f t h e 1 9 8 1 g r o w in g s e a s o n . H o w e v e r ,a s et o f o b s e r v a t i o n s g a v e i n f o r m a t i o n o n t h e b i o l o gi c a l a n d t e c h n i c a l a p p l i c a b i li t y o ft h e n e w c o n t a i n e r t y p e .Si te N o. 1: Neuharl ingersie l, No r th Sea

H e a v y f o u l i n g b y m u s s e l s (My t i l us my t i l us ) , b a r n a c l e s (Balanus balanoides) a n dh y d r o z o a n s t h r o u g h o u t t w o c o n t a in e r s w h i c h h a d n o t b e e n c l e an e d f r o m t h e b e g in -


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1 9 8 T H O M A S N E U D E C K E R

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F i g. 7 . F r o n t v i e w o f p r o t o t y p e c o n t a in e r ( d i m e n s i o n s in m m ) .

F i g . 8 . S p a t ( 3 0 - 4 0 m m i n s i z e , i n i t ia l l y ) g r o w n f r o m A p r i l t o A u g u s t 1 9 8 1 o n t h e i s la n d o fA m r u m , i n t h e N o r th S e a , r e a c h e d s m a l l m a r k e t s i z e an d s h o w e d a l m o s t u n i f o r m s h a p e .


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N E W O Y S T E R O N - G R O W I N G C O N T A I N E R F O R M A R I C U L T U R E O P E R A T I O N S 1 99

Fig. 9. Crassostrea gigas grew at angle of approximately 60 to a nicely shaped market oyster.On the islands of Amrum and Sylt, in the North Sea, there were no fouling problems.

ning of the test (1 April 1981) until the first set of observations (23 July 1981) leadto complete overgrowing of the oysters (Figs 10, 11 and 12). Continuation of the testwas therefore pointless at this site as cleaning of the oysters and containers was notpossible and the oak frames were broken in several cases due to the tremendousweight of the fouling organisms.S i t e N o . 2 : N o r d s t r a n d , N o r t h S e a

Heavy fouling, especially by barnacles which preferred to settle on the oak framesand the re-attachment cement beneath the oysters, gave serious problems. Whilegrowing, the barnacles had forced the oysters off the cement. At the time of the firstset of observations (2 July 1981), already 30.5% (513 specimens) were loose, while66-5% (1117 specimens) remained in position. Mortality at that time was 3-0%(50 specimens). Most oysters showed evidence of growth. However, the two bot tomframes were broken and the plastic mesh sheets in some cases torn out at the staplingspots. The container had not been cleaned since the beginning of the test (1 April1981).S i te N o . 3 : A m r u m , N o r t h S e a

Little fouling by barnacles was observed at the time of the first set of observations(13 August 1981) and most were dead. Almost all oysters (1556 specimens; 92.6%)


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200 T H O M A S N E U D E C K E R

F i g. 1 0 . S o m e b a r n a c le s , h y d r o z o a n s a n d n u m e r o u s m u s s e l s o v e r g r e w t h e o y s t e r s a n d o a k f r a m e sa t N e u h a r l i n g e r s i e l , N o r t h S e a .

F i g . 1 1 . W i t h o u t in s p e c t i o n a n d c l e a n i n g , c o n t a i n e r s m a y b e c o m e c o m p l e t e l y f o u l e d( N e u h a r l i n g e r s i e l ) .


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N E W O Y S T E R O N - G R O W I N G C O N T A I N E R F O R M A R I C U L T U R E O P E R A T I O N S 201

F i g. 1 2 . O y s t e r s c o m p l e t e l y f o u l e d b y M ytilus rnytilus.

w e r e i n p o s i t i o n ; o n l y 7 4 s p e c i m e n s (4 . 4 % ) h a d f a l le n o f f . M o r t a l i t y w a s o n l y 3 - 0 %( 5 0 s p e c i m e n s ) a n d m o s t o y s t e r s s h o w e d g o o d g r o w t h , a lm o s t r e a ch i n g t h e s m a ll e stm a r k e t s iz e . C o n t a i n e r s a n d f r a m e s s h o w e d n o s ig n o f d am a g e a n d h a d n o t b e e nc l e a n e d s i n c e t h e b e g i n n i n g o f t h e t e s t ( 1 0 A p r i l 1 9 8 1 ) .S i t e N o . 4 : S y lt , N o r t h S e a

V e r y l it t le f o u li n g , e x c e p t f r o m n u m e r o u s h y d r o z o a n s , w a s o b s e r v e d a t th e t i m e o ft h e f i r s t s e t o f o b s e r v a t i o n s ( 2 5 A u g u s t 1 9 8 1 ) a n d t h e o y s t e r s e x h i b i t e d e x t r e m e l yg o o d g r o w t h a n d s h a p e a t f i r s t s i g h t . H o w e v e r , t h e p l a s t i c n e t t i n g h a d b e e n t o r n o f fa t v a r i o u s p l a c e s o n t h e o u t s i d e f r a m e s , a d m i t t i n g s e a s t a r s (As ter ias rubens) . O n o n ef r a m e , e i g h t A s t e r i a s w e r e f o u n d w h i c h w e r e o f a b o u t 2 0 c m i n d i a m e t e r . I n a ll,3 1 A s t e ri a s w i t h a p p r o x i m a t e l y 2 . 7 k g o f b io m a s s w e r e in s id e t h e c o n t a i n e r a n d h a do b v i o u s l y k i l le d 6 3 - 7 % o f t h e o y s t e r s . I t a ls o s e em s p o s s ib l e t h a t m o s t o f t h e o y s t e rs he lls w h i c h w e r e f o u n d l o o s e o n t h e f r a m e s ( 2 4 6 s p e c i m e n s ; 1 4 -6 %) w e r e t o r n o f f b yA s t e r ia s . T h i s c o n t a i n e r h a d n o t b e e n c l e a n e d d u ri n g th e s u m m e r p e r i o d a n d h a ds h o w e d n o s ig ns o f s i l t a t io n s in c e t h e b e g i n n i n g o f t h e t e s t ( 1 0 A p r i l 1 9 8 1 ) .Site N o. 5: Langballigau, Ba ltic Sea

A l l c o n t a i n e r s ( f i v e ) w e r e s u b j e c t t o s e v e r a l o b s e r v a t i o n s d u r i n g th e s u m m e r s e a so na n d h a d b e e n c l e a n e d , d u e t o h e a v y m u s s e l f o u l i n g w h i c h o c c u r r e d i n J u l y , b y h o s i n g


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202 T H O M A S N E U D E C K E Roff. As the water pressure of the pump was approximately 5 bar, some of the oysterswere sprayed off during the cleaning process. Nevertheless, the loss amounted to only3.8% and mortali ty was 2.4%. One reason for mortality was the fact that some of thesmaller oysters had both valves in the cement as a result of re-at tachment and wereunable to open subsequent to this. 7845 oysters (93.8%) out of 8360 re-attached onesremained in position at the time of the last set of observations (31 August 1981).

In summarising the results and experiences gained in the first test of this newcontainer prototype, the following points should be noted.

1. The tests have demonstrated the biological and technical applicability of thenew container type, but technical improvements are necessary such as the useof rigid galvanised steel frames instead of oak frames.

2. A stronger and more seawater-resistant cement should be found.3. Regular checks on the oysters are necessary to prevent problems arising due to

fouling organisms.4. Anti-fouling coating against barnacles might be useful in some areas.5. Areas of intensive fouling are not suitable for the growing of oysters if main-

tenance work cannot be carried out.6. The cost of an improved container such as that described will be approxi-

mately DM 1400; this, from our experience with other containers, should lastat least 5 to 10 years.

7. Two men, according to skill and organisation, should be able to re-attachbetween 300 and 700 oysters h -~.

8. A container may be cleaned of fresh encrusting growth, by two men, withinapproximately 20 min.

9. The subjective observation of the growth and shape of oysters, which has yetto be proven by measurement, indicates that, using the new containers, theygrow to a relatively uniform shape (Figs 8 and 9), especially those which hadbeen re-attached at an angle of roughly 40 to the horizontal.

10. Growth rates in the North Sea may be much better than those in the Baltic Sea.11. On sandy sea beds and when subject to strong currentr, the prototype container

may not be sufficiently stable and may fall over. However, this would not bethe case if wider units were used.

D I S C U S S I O N

Oysters in natural beds compet ing for space and food normally grow upward (Galtsoff,1964; Korringa, 1976; Neudecker, 1980; Quayle, 1976). This is also the case if artificialsubstrates are presented, such as tarred lattices, which are in use in Australia (Korringa,1976). An upward position in the trays encouraged growth rates of C. gigas in Yugo-slavia (Stjepcevid, 1979). Therefore, the author believes that, according to the observa-


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NEW OY STER ON-GROWINGCONTAINER FOR MARICULTUREOPERATIONS 203t i o n s m a d e i n t h i s s t u d y , a n u p w a r d r e - a t t a c h m e n t o f f e r s t h e o p t i m a l p o s i t i o n a n ds p a c e fo r t h e g r o w t h o f a n o y s t e r u n d e r G e r m a n c o n d i t io n s .

T h e r e - a t t a c h m e n t o f o y s t e r s h a s b e e n t r ie d b y s o m e w o r k e r s t o i m p r o v e t h e s h a p eo f o y s t e r s a n d a i d m e c h a n i s a t i o n o f t h e c u l t i v a t i o n o f c u l t c h l e s s o y s t e r s ( R i l e y e t a l . ,1 9 7 2 ) . H o w e v e r , i n G a l i z i a , S p a i n , t h e r e - a t t a c h m e n t o f Osr tea edu l i s L . t o r o p e ss e e m s t o b e , to t h e a u t h o r ' s k n o w l e d g e , t h e o n l y c o m m e r c i a l l y v i ab l e i n d u s t r y u s in gt h is t e c h n i q u e . T h i s m e t h o d is n o t t r a n sf e r a b le t o G e r m a n si te s b u t t h e a t t e m p t s m a d ei n t h is s t u d y s t r o n g ly i n d i c a te t h a t i m p r o v e m e n t o f t h e p r o t o t y p e c o n t a in e r a s p r e -s e n t e d i n t h i s p a p e r c o u l d l ea d t o a n o y s t e r o n - g r o w i n g d e v ic e w h i c h o f f e r s g o o dp o s s i b i l i t i e s f o r o b t a i n i n g a h i g h p r o p o r t i o n o f w e l l - s h a p e d C gigas f o r c o m m e r c ia lp u r p o s e s a s w e l l a s f o r c o m p a r a t i v e s c i e n t i f ic s t u d ie s .

T h e i n v e s t m e n t o f D M 1 4 0 0 f o r a y i el d o f 1 6 8 0 o y s t e r s is f a r l es s t h a n t h e p r e s e n tc o s t o f c o n t a i n e r s w i t h c o m m e r c i a l p l a s t i c t r a y s a s d e s c r i b e d b y M e i x n e r ( 1 9 7 6 )w h i c h a r e p r e s e n t l y in u s e i n G e r m a n y ; t h e s e a l so re q u i r e c o n t i n u o u s t h i n n i n g - o u t o foys te r s and ca re aga ins t fou l ing , e spec ia l ly s i l t a t ion .

W h e t h e r t h e h o r i z o n t a l p o s i t i o n o f t h e r e - a t t a c h m e n t f r a m e s is t h e o p t i m a l o n e i sn o t y e t c l e a r b u t t e s t s a r e b e i n g c o n d u c t e d t o i n v e s t i g a te t h e e f f e c t o f v e r t i c a l p o s i t i o n -i n g o f t h e f r a m e s . O t h e r w o r k e r s h a v e p r o d u c e d v e r y g o o d g r o w t h a n d w e l l - s h a p e dC gigas a f t e r g r o w i n g t h e m h a n g i n g f r o m m e s h f r a m e s ( H u g h e s - G a m e s , 1 9 8 0 ) . A l s o ,n a t u r a l l y a t t a c h e d s p a t i n t h e J a p a n e s e l o n g -l in e a n d r a f t c u l t u r e s gi ve g o o d re s u l ts ,e x h i b i t i n g g r o w t h i n a ll d i r e c t i o n s f r o m t h e m o t h e r s he ll ( N e u d e c k e r , 1 9 8 l b ) .

F o r r e d u c in g l a b o u r a n d e q u i p m e n t c o s ts i n s uc h a m a r i c u l t u r e o p e r a t i o n , it w o u l db e w i s e t o r e - a t t a c h a s s m a l l o y s t e r s a s p o s s i b l e . H o w e v e r , s m a l l o y s t e r s t e n d t o g r o wa l o n g t h e s u b s t r a t e a n d n o i n f o r m a t i o n i s y e t a v a i l a b l e c o n c e r n i n g t h e o p t i m u m s i z eo f C. gigas f o r r e - a t t a c h m e n t i n t i l e d e s c r i b e d s y s t e m .

ACKNOWLEDGEMENTST h i s s t u d y w a s f i n a n c e d b y t h e G e r m a n M i n i s tr y o f R e s e a r c h a n d T e c h n o l o g y a n d t h eI n s t i t u t e o f C o a s t a l a n d I n l a n d F i s h er i es . T h a n k s a r e d u e t o m y a s s i s ta n t s M r s S .G e h e n d g e s a n d M r W. C l a u s e n a n d t o t h e p r i v a t e f i s h e r m e n i n v o l v e d a l o n g t h e N o r t hS e a c o a s t f o r th e i r e n g ag e d c o o p e r a t i o n a n d s u p p o r t .

REFERENCESGaltsoff, P. S. (19 64). The Am erican Oyster, U.S. Fish and Wildlife Service. Fish . Bul l . ,64 ,400-40 4.Hughes-Games (1980). Personal commu nication.Korringa, P. (1 976 ). Farming the cup ped oysters of the genus Crassostrea. Develop. Aqua. Fish.Sci., 2, 1-224.


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204 THOMAS NEUDECKERMeixner, R. (1976). Culture of Pacific Oysters (Crassostrea gigas) in containers in German coastalwaters. F A O , F I R : A Q / C o n / 7 6 / E . 2 8 .Neudecker, Th. (1980). Report on an information tour to North American oyster research stationsand commercial oyster farms, unpublished.Neudecker, Th. (1981a). Project report, unpublished.Neudecker, Th. (1981b). Report on an information tour to Japanese oyster research stations andoyster farms, unpublished.Quayle, D. B. (1969). Pacific Oyster culture in British Columbia. Fish. Res. Board Can. 169.Riley, J. G., Rowe, R. J. & Hidu, H. (1972). Oysters: Re-attachment as Method of Rearing Cultch-less Hatchery Oysters. Com mer cia l Fi sheries R evie w. Reprint No. 935.Stjepcevid, J. (1979). Personal communication.

neudecker 1982 aquacultural-engineering

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