CM_1981_F_11.pdf (560.9Kb)

This paper not to be cited without prior reference to authors - ^{··----~---_...,:.._} _____ .. ^~-·- ~---~~---~---~---·· - - - ·

International Council for the Exploration of the Sea

CM 1981/F:ll Mariculture Comrnittee Ref. Demersal Fish Cttee

LARGE-SCAIJE REARING OF COD FRY ( Q~_DU.e_ ~Q.RHU~) IN AN INLET

ABS'TRACT

by

Victor Øiestad,

Institute of Marine Research, N-5011 Nordnes Bergen, Norway.

and

Per Gunnar Kvenseth,

Institute of Fishery Biology, University of Bergen,

N-5011 Nordnes Bergen, Norway.

For two years cod larvae have been transferred to a large dammed pond (60 000 rn3

) after rotenon treatrnent of the system. Hydr·ography and stand ing crop of zooplankton and fish larvae have been monitored frequently.

Both year the cod larvae have had a very high feeding incidence and the whole population of larvae has started to grow fast with no fraction of emaciated larvae identified.

Large stocks of hydromedusae have probably preyed upon

the cod larvae until metamorphosis 35-40 days post- hatching.

In 1981, when no dam leakage interrupted the experiment, rnany thousand· cod fry reach~d a size of lO cm in late July, partly on a diet·from an automatic feeder.

In late auturnn 1981 most of the produced cod fry will be

released in coastal waters and a tagging and recapture program will be ~nitiated to give inforrnations on their subsequent biology.

-2- INTRODUCTION

Large-scale experiments with marine fish larvae in large basins have long traditions in Norway (Rognerud 1887,

Rollefsen 1946). This type of experiments with fish larvae was resumed in 1975. The experiments have included a number of commersial species and have been carried out in the

large out-door basins at Statens Biologiske Stasjon FlØdevigen, Southern Norway (Ellertsen et al~ 1981, Moksness and Øiestad

1979, Øiestad et al. 1976, Øiestad and Moksness 1981).

A rather high survival to the 0-group stage of most species was observed when they were released in an enclosure system

without predators. We wanted to examine to what extent this high survival rate could be obtained in natural sea pands. This

type of locations is very numerous along the Norwegian coast.

If reasonable high su~vival could be obtained with minor rnodifications of the system, these ponds coul~ be used to rear large nurnber of marin fish fry.

MATERIAL AND METHODS

In 1980 a natural 60 000 m3

large

p~nd

fish predators were ex~Prminated, about 0.6 mill cod.larvae at end of yolk sac stage were transferred from the laboratory to the pond 7 April. In 1981 the experiment was repeated with 0.5 mill cod larvae released 31 March.

Bo~h year the cod larvae were sampled by a two-chamber net hauled horizontally in distinct depths by means of a float.

Total filtration opening was O.J m , mesh size 350 um, haul 2 distance 70 m and speed 2 knop.

Zooplankton was also sampled in these net h~uls and besides pumping in one meter steps was carried out weekly. Pumping

-3-

time was 30 sec with a 80 l/min pump and the water was filtered acro~s a 40 urn mesh -sized net.

Hydrography, nutrient sa1ts and phytop1ankton was rnonitored week1y.

In 1980 on~ of the dams was opened in ear1y June. In 1981 the same dam was opened 27 June and a fine-meshed meta1 screen was rnounted across the opening to prevent escape of cod fry and intrution of unwanted fish.

In 1980 and 1981 starvation groups were established in the 1aboratory and in 1981 a1so ~ transport group (1arvae

being exposed to transport to and from the inlet) .

In May 1981 an automatic feeder was rnounted at a raft in the pond.

RESULTS

In 1980 we had increasing problems with dam leakage and the experiment was terminated two months after release of the cod ·larvae. In 1981 the leakage problem was rninor and results to the end of July are included.

Hydrography

Salinity was: both year about 32 o/oo except in the.more brackish surface water. The oxygen saturation was above 9 O % except for the very bot tom water where i t from· time to time was 50-90 % saturation.

The temperature is indicated in Fig.2 for 4 meter depth.

It increased from about 5°C at re1ease of larvae to 10-l2°C at metamorphosis and to a maximum of 16°c befare opening of the dam. For the rest of the period i t was about 16 °c.

Phz~oElankton

The spring bloom was dominated by Scel~tone~~ costratu~

and for the rest of the period the phytoplankton biomass was dominated by unidentified f1agellates.

-4- Zooplankton

Both year the hydromedusae were very numerous, with highest values in 1981 and with Rathkea octopunctata and Sarsia sp.

as the dominant species, Fig 3 and 4.

Rotifera were very numerous in early April both year with a decline in late April, Fig.5 and 6. Nauplii of calanoid copepods wereat a steady level during April while an increase in calanoid copepods was observed from mid-April, Figs. 5 and 6.

Dominating species were Cal~~~s ~~~~~rch~~us, Centropages hamatus and Pseudocalanus .§_1<2_!:!.9_atus.

The mean density of potensial prey organisms (rotifera and naup1ii) in the depth be1ow 3 meter where most fish larvae were distributed,was during first feeding 107 per litre in 1980 and 24 per 1itre in 1981, Figs. 5 and 6.

Cod larvae

The starvation groups had a 100 ^% survival for 15 days both year, Fig.7, and the same was observed for the transport group.

The catches of cod larvae dec1ined both year, but to a 1ower level in 1980, Fig.8. At metamorphosis the population estimates were at about 5 000 in 1980 and 30 000 in 1981.

The length increment was about the same both year and meta- morphosis was reached at day 35-40 post-hatching, Fig.9, giving a daily length increment of 0.24 mm and 0.23 mm for 1980 and 1981 respectively. From metamorphosis to th~ end of June 1981 the daily length increment was 1.1lmm while i t was only 0.83mm from then to the end of July.

The body height distribution used as an indicator of

starvation, did not decrease, Fig.lO, and the specific rate increase to metamorphosis was 6.2 % and 5.3 % in 1980 and 1981 respective1y~

The feeding incidence increased rapidly to 100 %, Fig.ll.

The initial diet was dominated by rotifera with an eventual

O^r-...

·-s-

changing to stages of calanoid copepods,in 1980. For 1981 no gut examination has been carried out so far.

DISCUSSION

From a maricultura1 point of view the high feeding incidence and high and homogenous growth rate w~s very promissing, Figs.

11 and 10. Seemingly no fraction of the population was at any time emaciated giving a potensial 100 % survival.

In 1980 the leaking would give a high loose of larvae

with out-flowing sea water as would predation from intruding fish.

Neglecting 1980 results, the reduction in 1981 might have been caused by hydromeØusae which is known to be predators on fish larvae (Fraser 1969, Lebour 1923).

The high daily length increment after metarnorphosis might partly be due to the food supply from the automatic feeder.

In previous basin experiments the produetion of 0-group cod have been regularly 0.9~1.0 perm 3 to a mean length of 7 cm. The final production of cod fry in the inlet this year will be clarified in late autumn.

PERSPECTIVES

Thesevery promissing initial r~sults will be followed up in future experiments where the hydromedusae will be tried exterminated.

The produced fry will primarily be tagget and released in

the region south of Bergen and the survival, rnigration, growth, pattern of fishing rnortality and recruitment to local spawning stocks will be investigated. Initial tagging experiments have been carried out with cod fry produced in the basin experirnent in 1976 and 1977, and a lO % return has been reported

(Moksness and Øiestad 1980).

-6-

A fraction of the fry will be reared to commersial size to 1ook at the pay back of an intensive culture of this species.

REFERENCES

Ellertsen,B., E.Moksness, P.So1emdal, S.Ti1seth, T.Westgård and V.Øiestad. 1981. Growth and survival of three 1arval populations of cod (Gadus morhua L.) in an enclosure. Experiments and mathematical model. In K.Sherrnan, Ed. ,In~.Coun.Explor.Sea Rapp.P.-V.R~un.,

Vol. 178.

Fraser,J.H. 1969. Experimenta1 feeding of some medusae and chaetognatha. ~.Fish.Res.Bd.Can. 26: 1743-1762.

Lebour,M.V. 1923. The food of plankton organisms II.

J.mar.biol.Ass.UK.Vol.l3:70-92.

Moksness,E. and V.Øiestad. 1979. Growth and survival experiment with capelin larvae (Mallotus villosus) in a basin and in.plastic bags. Int.C~un.Expl~r.S~~ CM 1979/F:53

(Mime o) .

Moksness,E. and V.Øiestad. 1980. Tagging experiments on 0-group coastal cod (Gadus morhua L.) reared in an outdoor

--~-- - - - -

basin. (In Norwegian with English summary)Fisken Hav., 4:11-20.

Rognerud, C. 18 8 7. Hatching c od in Norway. Bu.ll. U.S. F_~-~~-CO!)lm. , 7 (8): 113-119.

Rollefsen,G. 1946~ Kunstig oppdrett av flyndreynge1. In C.L.

Godske, Ed. , Forsk!!!E..SL_ og __ f~msteg. J. W. Eides Forlag, Bergen. pp. 91-113.

Øiestad,V.,B.Ellertsen, P.Solemdal and S.Tllseth. 1976. ·Rearing of different species of marine fish fry in a con-

structed basin. In G.Persoone and E.Jaspers,Eds. ,_!Oth European symposium on marine biology. Vol.l. Universa Press. Wettern, Be1gium.pp. 303-329

Øiestad,V. and E.Moksness. 1981. Study of growth and survival of herring larvae (glup~.~ harengus L.) using plastic bags and concrete enc1osure methods combined. In

K. Sherman 1 Ed. , ~:2!....:~o~n. Explor. Sea Rapp_~.~:!. Re'!.~. Vol.

178.

Fig.l. The inlet is situated close to the mari-culture station in Austevoll about 20 n.mils south of Bergen,

o ^l o '

at 60 .04 N and 5 .15 E. Depth contour lines and the two dams are indicated.

16 oc --- 1980 ... 4981

14 ^' ..

···

12

10

9

6 4

i , , , i ,M.A y, , , , ^{i ,}

l· , , ,

l· ,

Fig.2. Temperature at 4 m depth for 1980 and 1981.

...

"....-

~

n·-·

w L-~

o_

a--)

'-...i

z

800

500

·-

400

300

200

SARS! .A

i C:la

~

-~

o

L-.-,-+~:7: ~-2~~~ ^;17 ~~T ~ \1~

Fig.3. Mean number of hydromedusae perm 3 in 1980 at 4 m depth.

,rJ~:ri: 4Cm-

ffi 90]

a..

~ so

l!J

60 50 i()

20

__ ·- OTHERS

l

10

1---r---r---r-~'T'""'t-,..-~..,----,..--,-...,.·....,..,.._,--,---.-A-PR----r--...-·--r-'r"'""'"-r-t--r----.

Fig.4. Mein nu~b~r of hydromedusae per m3 in 1981 at 4 m depth.

1-~

_J

0:: UJ Q..

120

100

- - . RDTIFERA .

. . . NAUPLII ___ CAL. COP

o 80 z

0:: w

1- _J 0:: UJ

a.

o z

GO

5

40 2

20

MAY

o

Fig.S. Mean nurnber of rotifera (left coordinate), nauplii and calanoid copepods (right coordinate) per litre in 1980. Samples from 3m, 4m, 5m and bottom have been averqged.

_ _ ROTIFER,\

... NAUPLII - __ CAL,. COP

50 st.&J

0:: 1-

_J

40 0::

sw

o z

30

4 20

2 10

o

Fig.6. Mean nurnber of rotifera (left coordinate), nauplii and calanoid copepods (right coordinate) per litre in l9al. Samples from 3m, 4m, 5m and bottom have been averaged.

20

- - 4980 ... 4984

AGE IN OAYS

Fig.7. Mort.ality c:E starvdticn qroups in 1980 and 1.981.

t-o l: 4000 800000 a..

o o a::

S! _{- - 4980} ^u

500000 (!)

0:: 800 z

w . . . . 1981 -

a.. o

:t: 400000 ~

u l-< 800 ^(fl

u

300000 400

200000

200 100000

o _o

~-,-

Fig.8. Catches of cod larvae per 100m3 in 1980 and 1981 'left coordina ·b~) and stanc¹ ing· c rop (right coordina te) from re lease r.)nward, number released be ing O. 6 mi 11 j_ n 19 80 and 0.5 mill in ^19~1.

I 100·

r-

o w z

_J

o oc

<

2

r;:

z

w

C.!J D

_j

~ (}

1

l 1

-i l

i l

1 l

-=l

-l l

t ....$

;

4

l

l t

..J

!-"' ,. . . ~

:. ::: e

~;·-~

. . . . ^. . ^{. .} . ^{. .} . ^. . . ^....

//

•.

/

, . / .. ^",... ... /'' 198C

19f:i i

f ~

~

·l

i OØ

~-

~ t-

t-)

r ~ '

l l

t . l . l . ' l i

~t,,,, /..PR

'l'

~~n-rt-rtnt-n-JUNE-n-rT'n'JULYrrorrtn+

Fig.9. Mean standard length.of cod larvae from release to metamorphosis (left coordinate) and mean total Iength in June and July (right cooFdihate, only for 1981).

'•

.,_

:c

z w _,

_j

·<

t-

o

~

z <

w

\!.)

o -'

~500

:r:

l.U

:c

a

t)400

>-

I:

300

200

1-500 :c

IJJ :r:

1:

o t-400 o >-

l :

200

AGE 6 DAYS

o ²⁰

60

t-500 :r:

lJ.J J:

I:

o

E;400

>-

I:

300

200

AGE 10 OAYS

o 20 40 60

PER CENT _PERCENT

AGE 12 DAYS ·· AGE 4G DAYS

t-500 :r:

-

I: Q

t-400

' ) -

o

1:

300

200

o 20 40 60

PER CENT

Fig.lOa. Body height-frequency-distribution from release through first feeding for cod larvae in 1980.

PER CENT

1-500 :r:

lJJ

:c

l :

o t)400

>-

l:

300

200

,_500 :c

UJ

-

I

~

o f-400 o

>-

I:

300

200

o

o

AGE 6 OAYS

. 20 .ttCJ

PER CENT AGE

OAYS

20 40

PER CENT

,_500

J: (!)

:X:

w

I:

o

5400

>-

I:

200

r---500-

:r:

-

(!)

- w ::r:

o

~400

o

o

~m

>-

~

~

~

- - 300-

- - - -

l

(3

AGE 10 DAYS

20 i O

PER CENT AGE

%7.h1

~

l l l l ^{"l T 1 -T} l

2()

40

PER CENT

Fig.10b. Body height-frequency-distribution from re1ease through first feeding for cod 1arvae in 1981.

...

..

4990 f96 4

,-,._...._~~ ···-T~·-·~.,·-·'""-T··-·-·--·-r-"'"'---r · - - ,

iO 15

AGE IN DAYS

Fig.ll. Feeding incidence for cod larvae in 1980 and 1981.