,
,.
This paper' not to be eited without prior referenee to the author
International Coun~il for
the Exploration of the Sea
.'
' .. C .M.1912/F:21.
Demersal Fish (Northern) Committee i.'
Ref. Fisheries Improvement co~ttee
Tbe effect of population density on the growth of juvenile .. ·:'··,····
sole, Solea ~ (L).
by
1~,
•
B. R. Howell.
}arine Hatehery, Port Erin,
lsle of Man•.
and
O. Ledoux
Soeiete Civile Exploitation Agrieole du Domaine de Certes,
33-Audenge, France
......
IN'TRODUCTlON
.
An' important faetor in determining the feasibility of'commereial'
",
"
fish f~rtg'is the weight of fish ~hieh ean be produeed per ünltof
For each size of fish, produetion will depend on a num~er of
tankage.
faetors,' the most important··being tank size, water flow and st'Oeking
rat~.· 'The eval~~ion of each of these factors should ena:ble predlc-'
tions tobe·ina.de:concerning economie output.
':""l',_
In'this' paper the effect of stocking juvenile sole in small tanks at
vä.ri6;i~·;·densities under eonditions of eonstant water exchange is ex8i:nined. :
At the outset of the experiment little was known of the influence'of'
•
aecumulations of fish waste products, so that a water exchange rate whieh":.:would prevent any impairment of growth eould not be selected. Howeve:r,
'"j
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,.,.
•
eoncentrations'of ammonia, and itsoxidized derivatives, were monitored
and their possible effect is disoussed in relation to more reeent inve~tigations.
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x 30
..
'. . .
Tbe 'fiah ware "held ih' 60 x 30/om black polythene tanks'iiiuminated'"
from abov~ by"30iv 'daylight fluoro~oent tubes fo~12 ho~'s :in eaeh·'a.aY~: :.< :
Tbe tanks~ere:'-gehtly~erated'and:reoeived a flow of'5-1 litres perh~ür
..... '\ .,: .,....
, "
.
, . , '+ . 0
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,
of i'resh sea water. 'Air temperature was eontrolled at 15~0 - 1 ~O C~:"
but ':·b~ea.us~ the' temp~ratlire
the incoming seawater "was'not aciju~ted"
,
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:of
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tank temperatures i'luctuated,and deereased i'rom 15-16 C at the'beginning
to 12-13°C at the end oi' the experiment. For this reason it was not
1
"
possible to prevent the differential accumulation of metabolites by
irrigating
ea6hLt~in~i>r.O.I>~;df;i~n::.t~9.:.-th'$... ir~i..g.h.~,::· . ~r ..fi~~J:1._ ~~ ..~~~~~~D;~d..
The. tank~::~er~;arranged in two series of 8 and one cf 7;:~d stocked with
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:"I·"'~·.
...• , .. -i-'
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the föllowing·:approximate· riumbe'rsJoffish:
"
r"c
•..
Se;;i~~ C· , ... 20' ..'.'. 20 ',.- 4'0 ,.
60....·~ 80
""~"··"r.dTI;··
"lt~ ~.-
Series B.
150 200
f
Series·J·:A'·s.:' '-:~;o:") 2
it··
100
"':40
.,. " '." .;
~
80
100
200
40
20
60
j .•..
20
150
l\'~' G.?:~ '.. j:~:~.:; .190~:.:_?OP
The fish used had been rearcd from n single egg collcction and had
bcen weaned on to a diet of live Lunbricinus., n food "",hich allows good
growth of plaice (Kirk and Howaii, 1972).;,' A;~dom ~nmpTc' cf 168 fish
were weighed and measured at the beginning of thc experiment.
Sub-
sequent weighings were confined to series·::A. ond B at about 40 day inter-
'''1i./f'~ighod after 1'7 days',' series
ci~'s"'~tc~:""Tl~o~Xperimcntwas termin-
vals but staggered so that series N
B after 34 days, series A after 50
TO,~ac~.lt0.':·'
ated after 134 days, whon 0.11 fish were weighed and measured.
•
tate the .1lleasurementsand ,ta .avoid rdamnge the fish were first narööHze'(l'---'
6'
.
'.
....
'
solu~::i,on of MS222 (Sandoz).
with an '80 .parts/10
..'
.They "lere re~~~.,to ;j'.i
a cleaned tank filledwith fresh sea.water.
The stock was fed an
~
libitum diet of. ~"D.brici11us.o Follo,,,ing
of.f~sh in.s~rics
the weighings
convers~o~;ratios co~ld
.. .
11. and B after 50:and .34days rcspectively,c.'
the food added to each tank, and n:ny
food
. t·;····
foo~removed,
was weighed. so :that,,: ..~,
be·calculated•. Temperaturenwere recorded
daily, and 0. high standard. of· hygi.enc; was maitl~~ined by;. ~requ?n~ly ;.siph~Il~:,:.
ing accumulated dcbrisf~om the. ,tar..ks.
RESULTS
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a).Mortality
;Morta~ities
density.·
~perimcnt. were lowand,,~un-related.to
throughout:thc.
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b) Growth
. . .~j .. ,
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At the end of the experiment, after 134 dnys, the fish at thc
lowest ;density.:hadl?-<?hievedq...m.:..c'?:n..,~TCig9-t of around 8 g wh.ile those at
the highest dcnsity,had.reached.a
lI'.ean vrcight of.less thanAg.
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The
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relo.tionship
mean
w:cight
and ;density.
waD, similar
in. .. the
three,
. .
.. '. ;betwcen.
.'...
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'.-. .. . .,: -..'
.,
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series but(.the dat~.have not been. combined,. because. thc fishin each .
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The. ..rt
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series .had.: ~o~.?-t ;:.sligh~ly.
....diff.ercni;
rates
(Figure
. 1)."l' ;.''J;he...,devel.op.....
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...,
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ment
of' ·this .relationship
·for.
sories. A. is
sho,'ffi
·.inFigure
2.
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equations of the curves were determined from linear regression analyses
of logarithmic values of each parameter.
c) Relative variability
The-'p'öpulD:tT6u"'of fÜ3h"'usöd - tö .stock" the--experimont· was' very ..... "-' _.....
variabl€. in·weight,...as.indicatod. bythe.
approximately- 59%.
90e,ff;i9~oJ:l:tof variation
of
The grentest ..
chnngo
occurrod
over
the first 50 days,
,.
_
.when thoro was a general decrease in variability which.was donsity-'~"'
'~
dependont.
~."."
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Fish held at the lowcr densities became loss variable than
those held at the higher dcnsities.
There was little ::rurther·change.
during the remainder of the experiment nnd the final relationshipbetween
....
•
"
density ünd variability is shown in Figure 3. Thera 1ms a sighificant
positive cörrelation·betweon logarithmic values of density and theco~ffi•
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cient of-"varintion ..:f,oJ:....ßerios .A.nnd..C (p ~<; Q•. Q1.._and
P < 0.05.._.respectiv~iy),
. .... ....
__ ......
..... .....
but that of series E was not significant (p < 0.1).
d) Food conversion ratio
~
-~.--~---
In both series of tanks in which food intako was measured, fish
held at high density converted their food into body tissue less efficiently than those at low density (Figure
4).
Food conversion ratios,
calculated from wet weights of food and fish, ranged from 4.0:1 to
2.7:1.
DISCUSSION
. It is not possible to attribute the described differences in growth,
relative variability and food conversion efficiency to population
interaction alone, bccause the equal water exchange rates at all stocking densities resulted in a differential accuroulation of waste products.
~
This was most marked in series C, in which a ccmplete water change was
not made during the experiment (Table 1).
Recent work (Alderson, un-
published) indicates that these levels of ammonia are unlikely to havchad
DX1Y deleterious effect.
Althoueh there is no evidence to suggest that
thc high levels of nitrite and nitrate are harnful, the low pH values,
which indicate high carbon dioxide concentrations, are more likely to
have had an adverse effect on the fish.
REFERENCES
KIRK, R. G. and H01'lELL, E. R., 1972. Growth rates and food conversion
in young plaice (Pleuronectes platessa L.) fed on artificial and
natural diets.
Aquaculture
1 (1): 29-34.
3
TABLE 1. " Ammoni:l.• , nitri te; ni trr>.te r-tnd pH Vr-tlues far serie!:! C
towards the end of the experiment.
Density
'.
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.
pH (127 dnys)
Ammo;la (128dn.ys)
(mg unmonia N/I) ,
20
40
60
80
100
200
1.. 9 "
7.8
7.7
7.6
7.4
7.3
0.20
0.34
0.44
0.44
1.06
1.06
1.5
8.6
16.9
25.0
40.4
16.7
23.0
36.2
42.5
50.3
Nitrite (134 days)
(mg atOIa/I).
1.3
Nitr~te (134dn.ys)
'"' (mg atom/I). '
14.7
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.'_...~. :..:,- :.!.-\~ ~ ~_ .. :. . ..
·" ..i: . '
1·0
• Row A
o Row B
& Row C
0·9
-
c:n
. - 0·8
3
......
..c;
c:n
cu
•
3
c::
c
cu
E
c:n
~
07
0
0·6
0'5 L...-_-J~_---L
1·2
Fig.1
,.4
_ _--...L-----'--_--.a..~
"6
1-8
2·0
2·2
Log density (number per tank) 0
Regression of mean weight on density after 134
days for the 3 ·series of tanks.
.
•
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t_.~
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Gay 133
\~
w= 25 ·60
0 0'38
8'0
7·0
6·0
Oay91 W= 13'51
•
00'31
5·0
--
Cl
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c::
t::j
Q)
~
•
10
•
Oay.J.Q.
2·0
w=
•
2'76
00'14
~
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--'-~------+-----.-------a.
•
•
•
•
1·0
100
150
(number per tank)
between mean weight and density for series A
~
r
.
"70
0
• Row A
0
B
&
C
.
.
',65
o
B
~
0
::-
c:"1·60
--
.e
d
'L:
d
>
01·55
ccu:
u
cu
31'50
DI
....0
1·45
1'4
1'6
1'8
2·0
Log density I number per tanlc), 0
2·2
Fig.3. Regressions of log coefficient of variation on log
density after 134 days for the three series of tanks
A
0'62
•o
B
0·58
o
.
...
'e;;
...
o
d
e
o
0'54
cu
>
c:
o
u
-c
-....
o
•
0'50
o
•
DI
C
0·46
0,42
1·2
1·4
1·6
1·8
2·0
2·2
log density (number per tank), 0
Fig.4. Regressions 01 log, food conversion ratio on log. density for series A and B over the last 84 and 64
days of. the experiment respectively.