Lawson 1982 Aquacultural-Engineering

7/28/2019 Lawson 1982 Aquacultural-Engineering

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Aquacultural Engineering 1 (1982) 311-317

P O N D C U L T U R I N G O F C R A W F I S H I N T H ES O U T H E R N U N I T E D S T A T E S

T . B . L A W S O N a n d F . W . W H E A T O N

Agricultural Engineering Department, University of Maryland, CollegePark, Maryland 20742, USA

ABSTRACTDue to a s&nificant increase in the farming of crawfish by pond culture methods inthe southern United States this paper briefly summarises the current practice beingdeveloped there.

Crawfish are cultured in shallow, open ponds surrounded on all sides by levees. Thewater depth seldom exceeds 45-61 cm. Area may vary, but the most popular s&esrange from 2 to 16 ha. A rotation scheme involving rice and crawfish is generallypractised, with rk'e serving as fo od for the crawfish.

Good management technklues are required for maximum crawfish production. Oneessential element is circulation o f water through the ponds to keep dissolved oxygenconcentrations above 5 mg litre -1. With good quality water and proper managementa harvest of up to 2200 kg ha-lyr-a may be realised.

INTRODUCTION

C r a w f i s h a re f r e s h w a t e r c r u s t a c e a n s f o u n d n a t u r a l l y i n a l l c o n t i n e n t s o f t h e w o r l d ,e x c e p t A f r i c a . T h e r e a r e m o r e t h a n 3 0 0 s p e c ie s i n e x i s te n c e w i t h o v e r 1 0 0 k n o w n t oo c c u r i n th e U n i t e d S t a t e s ( A v a u l t et al., 1 9 7 2 ) a n d 2 9 s p e c i e s a r e f o u n d i n L o u i s i a n aS t a t e .

C r a w f i s h a r e k n o w n t h r o u g h o u t t h e s o u t h e r n U n i t e d S t a t e s b y s e v e ra l o t h e r n a m e s :c r a y f i s h , c r a w d a d s , m u d - b u g s a n d s p i n y l o b s t e rs . T h e y v a r y g r e a t l y i n s iz e a n d h a b i t a t .T h e s m a l l e r sp e c i e s m a y r e a c h o n l y 2 .5 c m i n l e n g t h w h i l e t h e l ar g e r c r a w f i s h m a yg r o w t o o v e r 2 5 c m . T h e y a r e f o u n d i n m o s t l o w - l y in g , w e t a r e as , w h e t h e r i t b e as w a m p , s m a l l s t r e a m o r a r o a d s i d e d i t c h . M o s t c r a w f i sh b u r r o w i n t h e m u d , b u t s o m em a y c h o o s e t o s p e n d t h e i r e n t i r e l iv e s a b o v e g r o u n d .

3 11Aquacultural Engineering 0144-8609/82/0001-0311/$02.75 Applied Science Publishers Ltd,England, 1982Printed in Great Britain


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3 1 2 T . B , L A W S O N , F . W , W H E A T O NT h e r e a r e c u r r e n t l y o v e r 20 4 0 0 m e t r i c t o n s o f cr a w f is h b e in g p r o d u c e d a n n u a l l y

i n t h e U n i t e d S t a t e s (H u n e r a n d B a r r , 1 9 8 0 ) . B y f a r t h e l a rg e s t s h ar e i s p r o d u c e di n L o u i s i a n a w h e r e o v e r 2 4 0 0 0 h a o f p o n d s a re c u r r e n tl y i n p r o d u c t i o n w i t h a na n n u a l c a s h v a lu e o f $5 1 m i l li o n ( C o o k , 1 9 8 1 ) . O v e r 45 3 m e t r i c t o n s o f c r a w f i s h a r eb e n g p r o d u c e d a n n u a l l y o n t h e W e st C o a s t i n C a l i fo r n i a a n d O r e g o n , w h i l e 2 3 m e t r i ct o n s a r e p r o d u c e d i n t h e G r e a t L a k e s r e g i o n ( H u r t e r a n d B a r r , 1 9 8 0 ) .

I n t h e p a s t m o s t L o u i s i a n a c r a w f i s h w e r e c a u g h t i n t h e w i l d w i t h i n t h e v a s tA t c h a f a l a y a R i v e r B a s in . H o w e v e r , d u e t o u n u s u a l l y l o w r ai n f al l c o n d i t i o n s i n th ep a s t t w o y e a r s , th e w i l d c r o p h a s b e e n r e d u c e d d r a s t i c a ll y , le a v in g m o s t l y p o n d -c u l t u r e d c r a w f i s h . A s a r e s u l t, p r i c e s h a v e s o a r e d a n d c ra w f i s h p r o d u c t i o n i n p o n d sh a s i n c r e a s e d d r a m a t i c a l l y i n n e i g h b o u r i n g T e x a s a n d M i s s i s s i p p i , w h e r e p r e m i u mp r i c e s a re p a i d f o r t h e c l e a n e r a n d b e t t e r t a s t i n g c r a w f i s h p r o d u c e d i n p o n d s . O v e r8 0 0 h a o f c r a w f i s h p o n d s a r e c u r r e n t l y ' p l a n t e d ' i n s o u t h e a s t T e x a s , a n d M is si ss ip p iis n o w e n t e ri n g t h e m a r k e t w i t h o v e r 6 5 0 h a o f p o n d s b e i n g p l a n n e d f o r p r o d u c t i o n b ye a r l y 1 9 8 2 ( R u t z , 1 9 8 1 ) .

T h e f a r m e r s h a v e l i t t l e t r o u b l e m a r k e t i n g t h e i r c r a w f i s h , m o s t b e i n g s o l d r e t a i l a tr o a d si d e s t an d s , f r o m t h e b a c k o f p i c k u p t r u c k s , o r e v e n o v e r t h e c o u n t e r i n f i shm a r k e t s . T h e c o o p e r a t i v e d e v e l o p e d i n M i s s i s s i p p i , b u y i n g c r a w f i s h f r o m f a r m e r s a n dr e- se ll in g t o t h e c o n s u m e r , i s h a n d l i n g 45 0 k g o f c r a w f i s h e a c h d a y d u r in g t h e g r o w i n gs e a s o n ( R u t z , 1 9 8 1 ) .

O n a n a n n u a l b a si s t h e a v e r ag e c r a w f is h f a r m e r c a n e x p e c t t o p r o d u c e 5 6 0 - 1 1 0 0 k gh a - ~. T h e w e l l -m a n a g e d c r a w f i sh f a r m s h o u l d b e c a p a b l e o f p r o d u c i n g u p t o 2 2 0 0 k gh a - 1 . A t a s e a s o n - o p e n i n g p r i c e o f $0 . 68 k g 1 in s o u t h e a s t T e x a s d u r i n g t h e s p r in g o f1 9 8 2 , o n e c a n i m a g i n e t h a t c r a w f i s h f a r m i n g c a n b e qu i t e p r o f i t a b l e .

T h e c r a w f i s h ' c a t c h ' i s p r e d o m i n a n t l y c o m p o s e d o f t w o s p e c i e s . T h e r e d s w a m pc r a w f i s h Procambarus clarkii m a k e s u p a b o u t 7 0 %, w h i l e t h e w h i t e r i v e r c r a w f i s hProcambarus acutus, t h e r e m a i n d e r . T h e r e d s w a m p c r a w f i s h is n a t i v e t o t h es o u t h e r n U n i t e d S t a t e s a n d t h e M i s s i s s i p p i Va l l e y , b u t h a s b e e n i n t r o d u c e d i n t oC a l i f o r n i a , O r e g o n , N e v a d a , S o u t h C a r o l i n a , V i r g i n i a a n d M a r y l a n d a s w e l l a s C e n t r a lA m e r i c a , A f r i c a , H a w a i i a n d J a p a n ( H u n e r a n d B a r r , 1 9 8 0 ) . I t h a s a ls o b e e n i n tr o -d u c e d i n t o E u r o p e a n d S c a n d in a v i an c o u n t r i e s w h e r e t h e n a t u r a l cr a w f is h p o p u l a t i o n sw e r e w i p e d o u t b y t h e ' c r a y f is h p l a gu e f u n g u s ' a d e c a d e a g o.

D E V E L O P M E N T O F P O N D M A N A G E M E N T

Site and water sourceC r a w f is h a re c u l t u r e d i n s h a ll o w , o p e n p o n d s a n d t h e p o p u l a r m e t h o d o f c u l tu r e is

t o r o t a t e t h e c r a w f i s h w i t h r ic e , w h i c h p r o v i d e s f o o d f o r t h e m .T h e m a n a g e m e n t p r a c t i c e d e s c r i b e d b y H u n e r a n d B a r r ( 1 9 8 0 ) , d e v e l o p e d f r o m

e a r li e r p r o c e d u r e s s e t o u t b y L a C a z e ( 1 9 7 0 ) a n d H i l l a n d C a n c i e n n e ( 1 9 7 2 ) , is s i m i l a rf o r m o s t o f t h e s o u t h e r n U n i t e d S t a t es . In m o s t c a s e s t h e l a n d s e l ec t ed f o r c ra w f i s h i s


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PO N D CU L T U RI N G O F CR A WFI SH I N T H E SO U T H E RN U N I T E D ST A T E S 3 1 3f l at , l o w - l y i n g , m a r g i n a l l a n d w h i c h h a s l i tt l e v a l u e f o r a n y o t h e r p u r p o s e . I t h a s t o b elo c a t e d n e a r a s o u r c e o f g o o d q u a l i t y s u r f a c e o r we l l wa t e r , a s t h i s w i ll d i c t a t e t h e s i zeo f t h e c r a w f is h f a r m .

T h e a r e a w h e r e p o n d s a r e t o b e l o c a t e d s h o u l d b e c le a r e d o f t r e e s, s tu m p s , o u t -c r o p p i n g s , e t c . , a s f a r a s p o s s i b l e . W o o d e d p o n d s a r e u s e d f r e q u e n t l y i n L o u i s i a n a ,b u t p r o d u c t i o n i n th e s e p o n d s is g e n e r a l ly m u c h l o w e r , a n d t h e c r a w f i s h a r e m o r ed i f f ic u l t t o h a r v e s t . I n a d d i t i o n , t h e h i g h o r g a n i c l o a d in g i n t h e s e p o n d s o f t e n re s u l t si n m o r e r a pi d o x y g e n d e p l e t i o n .

S o i ls a l so p l a y a n im p o r t a n t r o l e a t t h e s i te s i n ce a h ig h e n o u g h c l a y c o n t e n t i sn e c e s s a r y t o k e e p t h e w a t e r i n t h e p o n d s . L i m e t o o m u s t o f t e n b e i n c o r p o r a t e d i n t ot h e s o il s. E n o u g h l i m e m u s t b e a d d e d t o b r i n g t h e s o il p H u p t o a b o u t 6 - 7 - 7 - 0 ( A v a u l te t a l . , 1 9 7 2 ) a n d o n c e t h e p o n d s a r e f l o o d e d t h is a m o u n t o f li m e is e n o u g h t o m a i n t a i nth e h a r d n e s s o f t h e wa t e r a b o v e 1 0 0 m g l i t re - 1 , s in c e b e lo w 5 0 m g l i tr e - 1 c r a w f i s hs h el ls w i ll b e c o m e s o f t , a n d p r o d u c t i o n f al ls d r a m a t i c a l ly .I f s u r f a c e w a t e r is u s e d , r u n - o f f f r o m n e a r b y l a n d m a y b e a p r o b l e m . W a t e r h e a v i l yl a d e n w i t h i n s e c ti c i d es s h o u l d n o t b e u s e d a n y w a y s in c e c r a w f i s h a r e p a r t i c u l a r l ys e n s i ti v e . He r b i c id e s a n d p e s t i c i d e s a r e l es s t o x i c b u t m a y a l s o b e l e t h a l. T h e t o x i c i t yo f c e r t a i n p e s t i c i d e s a r e d i s c u ss e d i n H u n e r a n d B a r r (1 9 8 0 ) .

A n o t h e r p r o b l e m w i t h s u r f ac e w a t e r is t h a t u n w a n t e d f is h c a n e n t e r t h e p o n d s . T h ewa te r s h o u ld b e f i l t e r e d t o r e m o v e e g g s , l a r v a e a n d s m a l l fi s h , s i n ce r o g u e fi s h c a nc o n s u m e n u m e r o u s y o u n g c r a w f i s h .

T h e p r o b l e m w i t h w e l l w a t e r i s t h a t i t w i l l b e l o w o r c o m p l e t e l y d e v o i d o f o x y g e n ;h o w e v e r , i t d o e s o f f e r t h e b i g a d v a n t a g e , i n t h a t i t is f re e o f p es t i ci d e s a n d u n w a n t e df is h . In b o t h c a s e s i t i s n o r m a l t o a e r a t e b e f o r e t h e w a t e r e n t e r s t h e p o n d .P o n d c o n s t r u c t i o n

W ith t h e s i t e c l e a r e d , t h e a r e a m u s t b e l e v e ll e d a n d l e v e es c o n s t r u c t e d . T h e so ilu s e d t o c o n s t r u c t t h e le v e es is ' b o r r o w e d ' f r o m w i t h i n t h e i m p o u n d e d a r e a. T h e s i zeo f t h e i n d i v id u a l p o n d s i s d e p e n d e n t u p o n m a n a g e m e n t c a p a b il i ti e s, c o s t s , l an d av ai l-a b le a n d v a r i o u s o t h e r f a c t o r s . I n L o u i s i a n a a n d T e x a s t h e p o n d a r e as v a r y f r o m2 t o 1 6 h a .

A l t h o u g h c r a w f i s h p o n d s a r e n o r m a l l y b u i lt t o a d e p t h o f 3 0 - 6 0 c m , d e e p e r p o n d sm a y b e r e q u ir e d i n a re a s w h i c h h a v e a h o t t e r s u m m e r t h a n t h e s o u t h e r n U n i t e d S t at es .T h e p o n d s a r e e n c l o s e d o n a ll s i de s b y l e v ee s , t h e c r o w n s o f w h i c h s h o u l d b e a t l ea s t3 0 c m a b o v e t h e w a t e r l ev e l w h e n t h e p o n d i s f u ll . L e v e e s sh o u l d b e w i d e e n o u g h o na t l e as t t w o s i de s o f t h e p o n d t o p e r m i t v e h i c u l a r a c c e s s t o t h e p o n d s . T h i s g e n e r a l lyr e q u i r e s a l e v e e c r o w n w i d t h o f 3 - 3 - 7 m . T h e r e m a i n i n g l e v ee s s h o u l d h a v e a c r o w nw i d t h o f a t l e as t 1 - 2- 1 .5 m s o th a t c r a w f i s h w i l l n o t b u r r o w c o m p l e t e l y t h r o u g h t h el e ve e a n d c a u s e l e a k ag e . T h e s id e s lo p e s s h o u l d b e 3 : 1 o n t h e i n s id e a n d 2 : 1 o n t h eo u t s i d e , d e p e n d i n g u p o n s o il c h ar a c t e ri s t ic s .

W a t e r f l o w t h r o u g h t h e p o n d s i s d i r e c t e d s u c h t h a t ' d e a d ' a r ea s a re a v o i d e d . T h i s c a nb e a c c o m p l i s h e d w i t h t h e u s e o f d i v e r s io n l e v ee s w i t h i n t h e p o n d , a s s h o w n i n F i g . 1 .


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3 1 4W A T E R E N T E R S

A N D A E R A T E S H E R E

L ~ l z " / / / / f /

T . B. L A W S O N , F . W . W H E A T O N

O U T ER L E V E E S

W A T ER C I R C U L A T I O N R O U TE

J )(

D I V E R S I O NL E V E E S

IP O N D C O N T A I N I N G R I C E I

IN D C R A W F I S H

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OUTLETFig. 1. Crawfish po nd with inner diversion levees to aid water circulatio n.

T h e d i v e r s io n l e v e es d o n o t n e e d t o b e a s w i d e a n d h i g h as t h e m a i n w a l l s, b u t s h o u l db e o f s u f f ic i e n t h e i g h t s o t h a t t h e c r o w n a l w a y s r e m a i n s a t le a s t a f e w c e n t i m e t r e sa b o v e t h e w a t e r s u r fa c e . B y u se o f t h e s e d i v e r si o n s t h e p o n d e s s e n t i a ll y f u n c t i o n s a sa ra c e w a y , a n d a l l o f th e w a t e r m a y b e f l u s h e d f r o m t h e p o n d . S p a c i n g o f t h ed i v e r s io n l e ve e s d e p e n d s u p o n t h e s iz e o f t h e p o n d a n d i s m o r e o r le s s a m a t t e r o fj u d g e m e n t s i nc e r e s e a rc h o n t h i s a s p e c t is l i m i t e d .

I f i m p r o v e m e n t i n o x y g e n c o n t e n t i s t o b e a c h i e v e d b y r e c i r c u l a t i o n , t h i s o p e r a t i o n ,w h e n p u t i n t o p r a c t i c e , w i l l i n c r e a se t h e f l o w r a t e t h r o u g h t h e p o n d . U n f o r t u n a t e l y , o nl a rg e p o n d s t h i s s t il l w i l l n o t o v e r c o m e t h e p r o b l e m o f l o w o x y g e n v a l u e s a t t h e o u t l e t .F o r t h i s r e a s o n i t is r e c o m m e n d e d t h a t t o t a l i n d i v id u a l p o n d s iz e b e k e p t t o am a x i m u m o f 1 6 - 2 0 h a . A n y p o n d c o n s t r u c t io n m u s t b e c o m p l e t e d s o t h a t i t c a n bef l o o d e d b y t h e e n d o f M a r c h s o t h a t i t c a n b e s t o c k e d f o r t h a t s e a s o n .


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P O N D C U L T U R I N G O F C R A W F I S H I N T H E S O U T H E R N U N I T E D S T A T E S 315P o n d c y c l e

With newly prepared ponds it is normal to stock with 'brooders' at the rate ofabout 56 kg ha -a, 50% being female, in March/April. If native crawfish are alreadypresent, the amount stocked may be reduced by half, and once stocked, the pond neednever be stocked again unless some event should occur to wipe out the entire crop.

Drainage of the ponds should commence toward the end of May so that the pondsare drained over a two-week period. It is suggested that this rate should lower thewater level by about 7.5 cm per 48 h. The ponds should be completely drained bymid-June. By slowly draining the ponds in this manner the crawfish are forced toburrow deep into the soil in the pond bottom where they mate and raise their young.

During the next 30-day period the dry pond bottoms are cultivated, fertilised andlimed (if necessary) so that the rice may be planted by mid-July. Various varieties ofrice have been tried, and it would appear that some varieties provide greater crawfishproduction than others. In Texas, two rice varieties, gaining in popularity, are La Belleand Melrose (Davis and Kachtik, 198 l a).

Cultivating the first few centimetres o f the soil surface will not disturb the crawfishsince, by this time, they have burrowed deep into the soil. Research has shown thatcrawfish can burrow down 61-101 cm (Avault e t a l . , 1972).

In early to mid-September, by siphoning water out of the burrows, it can be deter-mined if they contain young crawfish, and when they are found in the majority of theburrows the ponds are flooded. They are usually flooded rapidly to take advantage ofthe warm weather in the South. However, since the weather is still quite warm throughSeptember, flooding may be delayed for two weeks. However, it should be completedby the first week in October or the young crawfish will begin dying in the burrows.

At this stage low oxygen conditions can occur in the ponds with the weather stillwarm, so the water may have to be circulated and aerated.

It is possible to begin harvesting the first November after stocking the ponds. Thecatch at this time will be modest and will consist of the adults stocked in the spring,the 'wild' adults present when the ponds were constructed and the first year youngwhich have reached harvestable size. Harvesting continues through till early June o fthe following year at which time the ponds are drained. Throughout the spring thecatch increases as the young crawfish reach harvestable size. Harvesting could cont inuethrough the summer, but at this time the shells become very hard and the meat tough.H a r v e s t i n g

Crawfish are harvested by trapping. Some traps are made of galvanised chickenwire, while others are made of plastic. The most popular trap is conical-shaped madefrom 1-9 cm mesh chicken wire coated with plastic (Fig. 2). The traps are weighted atthe bottom to prevent tipping over, have a bait in the centre and usually have three orfour funnel-shaped entrances where, theoretically, the crawfish enter but are unableto leave. The 1.9 cm mesh size commonly used to construct the traps allows captureof crawfish greater than 7.6 cm in length (considered the minimum marketable size).


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3 1 6 T. B. LAWSON, F. W. WHEATON

~10m

.. ~ ~ ~ 30-60cm

I

Fig. 2. Method of trapping crawfish. T, trap; WS, water surface; BW, bait well; EF, entrancefunnels.

T h e n u m b e r o f tr a p s u s e d p e r h a v ar ie s , b u t i t is u s u a l l y b e t w e e n 2 5 a n d 4 0 . T h et r a p s a r e b a i t e d w i t h p i e c es o f f is h a n d ' r u n ' o n c e o r t w i c e e a c h d a y . H a r v e s t i n g u s i n gt r a p s h a s b e e n t h e s u b j e c t o f c o n s i d e r a b l e r e s e a rc h o v e r t h e y e a r s , si n c e, d u e t o t h el a b o u r - in t e n s i v e n a t u r e o f t h i s p h a s e o f t h e o p e r a t i o n , i t c a n o f t e n e x c e e d 5 0 % o f t h eg r os s i n c o m e . T h e o l d m e t h o d o f h a rv e s ti n g in v o lv e d a m a n w a l k in g t h r o u g h t h e p o n dp u l li n g a w a s h t u b b e h i n d h i m . H e w o u l d d u m p t h e c r a w f i s h i n t o t h e t u b a n d r e -b a itt h e t r a p . T h i s m e t h o d is b y f a r t h e s l o w e s t a n d l e a st p r o d u c t i v e .

A m o r e s o p h i st i ca t e d m e t h o d o f h ar v e st in g u se s a m o t o r i s e d b o a t a n d a t w o - m a nb o a t c r e w ; o n e m a n e m p t i e s t h e t r a p s a n d t h e o t h e r m a n b a i t s a n d s e ts t h e t ra p s b a c ki n t o t h e p o n d . W i t h e x p e r i e n c e d o p e r a t o r s , b e t w e e n 2 0 0 a n d 4 0 0 t r a p s c a n b eh a r v e s t e d p e r h o u r .

A t h i r d h a r v e s t in g m e t h o d i n vo l v es t h e u s e o f a c r a w f i s h ' m u d b u g g y ' . T h i s f o u r-w h e e l d r iv e m o t o r i s e d v e h i cl e r e q u i r es o n l y o n e o p e r a t o r . H a r v e st ra t e d r o p s to 2 0 0t r a p s p e r h o u r , b u t a b ig a d v a n t a g e , b e s id e s c u t t i n g l a b o u r c o s t s in h a l f, i s t h a t t h e m u db u g g y c a n c r o s s l e v e e s , wh e r e a b o a t m u s t b e h o i s t e d u p a n d c a r r i e d a c r o s s t h e l e v e e s .

M a n y o t h e r l a b o u r s av in g h a r v e s ti n g t e c h n i q u e s h a v e b e e n t e s t e d b u t n o t y e ta d o p t e d b y t h e i n d u s t r y . C u r r e n tl y , a n a u t o m a t e d h a r v es t in g s y s t e m i s b e in gr e s e a r c h e d a t L o u i s i a n a S t a t e U n i v e r s i t y ( C o o k , 1 9 8 1 ) .W a t er q u a l i t y p a r a m e t e r s ( D a v is a n d K a c h t i k , 1 9 8 1 b )L i k e a n y o t h e r c u l t u r e d a q u a t i c a n i m a l c r a w f i s h r e q u i r e a n a m p l e s u p p l y o f g o o dq u a l i t y w a t e r , a n d h i g h p r o d u c t i o n r a t e s c a n o n l y b e a ch i e v e d i f a s u f f ic i e n t o x y g e nc o n c e n t r a t i o n c a n b e m a i n t a i n e d . I d e a l l y , c r a w f i s h w i l l f a r e b e t t e r i f t h e o x y g e nc o n c e n t r a t i o n c a n b e k e p t a t 5 m g l i tr e - a a n d a b o v e , b u t t h e y w i ll d o q u i te w e l l a tc o n c e n t r a t i o n s a s l o w a s 2 - 3 m g l it r e - a. I m m a t u r e c r a w f i sh , l e ss t h a n 5 c m i n l e n g t h ,r e q u i r e a t l e a s t 1 .5 m g l i t r e - 1 t o s u r v iv e a n d 3 m g l i tr e - 1 o r h ig h e r t o g r o w r a p id ly .

D u r i n g t h e w a r m e r m o n t h s w h e n p o n d v e g e t a ti o n is d e c a y i n g a n d o r g an i c m a t t e rb u i ld s u p , o x y g e n c o n c e n t r a t i o n i n t h e p o n d c a n d r o p q u i t e r a p i d ly . S i n ce th e s h a l lo wp o n d d e p t h l im i t s t h e e f f e c t iv e n e s s o f c o n v e n t i o n a l m e c h a n i c a l a e r a t o r s , g r a v i t y a e r a-


7/7

POND CULTURING OF CRAWFISH IN THE SOUTHERN UNITED STATES 3 1 7

tion followed by circulation through the ponds is the most c ommo n aerationtechnique currently employed in the industry.

The opti mum pH for crawfish is 7.0, with the recomme ndati on that the pondwater be ke pt betwe en 6.7 and 7-5. Grow th rates are noti ceab ly affected when the pHdrifts outside these limits.

In labora tory experi ments crawfish have survived 20]/00 salinity as sodium chloride.No field experiment s have resulted in crawfish surviving in greater than 12%o. Asalinity of 80/00 is generally recomm ende d as the upper limit for crawfish product ion.

Finally, water temperatures of 32C or higher are lethal to crawfish if the tempera-ture is allowed to remain at this level for 4 h or more. The most rapid growth occursbetween 21C and 23C, and feeding ceases at 13C or below.

REFERENCESAvault, J. W., de la Bretonne, L. & Jaspers, E. J. (1972). Culture of crawfish: Louisiana's crustaceanking. The American Fish Farmer, 1 (10), 8-14, 27.Cook, K. (1981). Louisiana researchers analyse crawfish trapping methods in cost-cutting study.Aquaculture Magazine, 8 (1), 10-12.Davis, J. T. & Kachtik, D. (Eds) (1981a). Texas Agricultural Extension Service, Southeast TexasCrawfish Newsletter, No. 7, Texas A & M University.Davis, J. T. & Kachtik, D. (Eds) (1981b). Texas Agricultural Extension Service, Southeast TexasCrawfish Newsletter, No. 8, Texas A & M University.Gooch, D. (1980). Crawfish farming in Louisiana. Proceedings of the First National Crawfish

Culture Workshop, University of Southwestern Louisiana.Hill, L. & Cancienne, E. A. (1972). Grow crawfish in rice fields. Co-operative Extension ServicePubhcation No. 1346, Louisiana State University.Huner, J. V. & Barr, J. E. (1980). Red swamp crawfish: biology and exploitation. Sea GrantPublication No. LSU-T-80-001, Louisiana State University.LaCaze, C. (1970). Crawfish farming. Fisheries Bulletin No. 7, Louisiana Wildlife and FisheriesCommission, Baton Rouge.Rutz, G. (1981). Mississippicrawfish industry growing. Aquaculture Magazine, 7 (6), 13-14.

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Lawson 1982 Aquacultural-Engineering