Fl@jeviger rapportser.,i, 1984, SSSN 0333-2594 The Propagation of Cod .::-;,:h!2 ?rL,p;.,c; L.
DEVEZOO!4-:ENT AND MORTP-LITY OF COD (G zd:r: ,-c rhi4 : L. 1 EGGS AND LARVAE IN DIFFERENT TZXPERATURES
S.A. Iversenl and D. S. Danielssen"
I Instlrute of Marlne Research, P.O.Box 1850, U-5011 K09RNES Norway
2 Fladevlgen Brologlcal Statlon N-4800 ARENDAL Norway
ABSTRACT
Iversen, S.A. and Danlelssen, D.S., 1984. Development and mortallty of cod ( i a d z z s ~ o p h ~ a L. ) eggs and larvae ln a~fferenr temperatures. In: E. Dahl, D.S. Danlelssen, E.
bfoks~ess and P. Soiemdal (Edi~ors), The Propagation of Cod
? & d u b m c r h u o L. Fleaevlgen rapportser., 1, 1984: 49-65.
expersment was carrled out as a part of a project
concerning tnermal pollution from a power plant. The paper deals wlth development and morrallty of cod eggs and larvae In dlf ferert temperatures (6O-18'~)
.
Eggs and larvae were exposed to hlgher temperatures for parrs of the rncubatlon tlme and the yolk sac perlod. The development rate lncreased wlth lrlcreaslng temperatures. The mortallty lncreased slg7lflcantly above 12OC, but was rather low below thls temperature. Newly fertrllzed eggs exposed to hrgher tem- peratures seened to be affected more seriously than eggs exposed to hlgher temperarures laxer In rhe lncubatlon perlod. Kewly hatched cod larvae exposed to hlgh tempera- tures showed no signrflcant rncrease rn the mortallty rate.The yolk sac perlod decreased wlth rncreaslng temperature.
Short temperature shocks (at about ~ O O C for 15 mln) dld nor affect rhe ~ortallty rate of eggs and larvae slgnlflcantly.
INTRODUCTION
The present investigation was carried out as part of a project on the influence of high temperatures on marine organisms in connection with thermal effluents of sea water from a nuclear power plant. The aim was to investigate the effect of high temperatures on the development and mortality of fish eggs and larvae. The present paper deals with the results on these stages of the cod. Experiments with both long-term high constant temperatures, and short-term shock temperatures have been carried out at different developmental stages.
MATERIAL AND METHODS
The eggs were artificially fertilized in a small jar with a little seawater added at about ~ O C , which is the natural spawning temperature. After 2-3 min the excess of milt was washed out and the eggs were transferred into an aquarium with running seawater with a temperature of 6'~. To get homogeneous egg material only one male and one female fish were used.
The eggs were transferred directly from 6 C to the experi- 0
mental temperatures of 6O, 8O, loo, 12O, 14O, 16O and 18Oc in the following developmental stages: laa (blastula stage), 1bS (gastrula stage), and 3 8 (late stage with a developed, but heart not beating). Egg development was defined from a scale described by Westernhagen (1970). Newly hatched larvae were also transferred to the same experimental temperatures.
The temperature was automatically regulated in water baths to an accuracy of +0. 1°c. The aquaria, which were held in the water baths, were perspex cylinders with volumes of 4.9 and 8.9 1. The outlet was through a strainer just above the bottom, the flowrate being c. 0.3 l/min (see Fig. 1).
Fig. 1. The experimental aquarium with the temperature regulation unit. 1. Outlet with a filter, 2. Aquarium, 3.
Water bath, 4. Water inlet, 5. Tap, 6. Mixing valve, 7. Cold water, 8 . Warm water, 9. Regulation unit, 10. Temperature sensor.
The seawater used was pumped in from 75 m depth with a salinity between 35.0 and 35. s0/0o during the experimental period.
The development and mortality were assessed once a day, and dead eggs and larvae removed. The larvae were not fed during the experiment; the experiments therefore continued until 100% mortality, except in 16' ar.6 18 C experiments with 0
eggs from the 3 6 stage, which had to be stopped earlier due to technical reasons.
In another experimental series, carried out in the same way as mentioned above, the experiments were terminated the day after 100% hatching. The larvae were then examined for abnormalities of body form or behaviour. Dead eggs and larvae were also removed once a day in this experiment and classified as abnormal or not.
To simulate the temperature conditions in the cooling water of a nuclear power plant, eggs in stage laa, lb0, 36
and newly hatched larvae were transferred ciirectiy fron ~ O C
to aquaria with temperatures about 10 deg C higher. They were held there for about 15 min, and the temperature was then regulated back to 6OC in 15-20 min. Control experiments at 6Oc were carried out with eggs and larvae fron the same material. The egg experiments were terminated the day after 100% hatching, and the number of abnormal larvae examined.
Egg development
The development of the eggs exposed to the different temperatures from the develop~ental stages laa, lbR and 38 are shown ln Figs. 2 , 3 and 4. Start of hatchlng (H), 50%
and 100% hatched are lndlcated rn the f~gures. The experl- wept wlth the youpgest eggs at 6OC was termrnazed when 50% of the eggs nad hatched. In tnls experrnent rhe developmertai rate rncreased w ~ t h increasing temperature up to 12OC. Ac temperatures of 14@, 16 and 18°C no development was observed o and the eggs died.
ay exposrng the eggs to drfferent temperatures from a later, stage lb5 (Fig. 3 1 , rrhev neveioped even at 14@C a m also to some extent rnltlally at lbo and 18OC. The develop- mental rate Increased wlth lncreasrng temperature up to 12 C. 0
At 1 4 O ~ the developmental rate rras slwllar to that a.; ? ~ O C , lndlcatlng a retardatron. The eggs exposed to the expcrl- mertal temperatures eve11 later at stage 3 8 hatched at all temperatures except 1 8 O ~ (Flg. 4). Even for the eggs exposed so late, a substa~tral drfference rn developmentai race was observed. The time to hatchlng was about two days at 1 6 O ~ and frve days at ~ O C .
1
5
10 15 20 D A Y SFlg. 2. Egg development rate In different constanr tempera- tures from the firs?, blastula stage (iaa) and onwards. H:
hatchrnq beglns.
Mortality with temperature
AS mevtloned earller, no mortallty could be est~mated for the eggs exposed at 6Oc from stage iaa. In the same experr- ments no difference In mortality was observed at 8O and IOOC (Flq. 5). Above thrs temperature the mortallty Increased rapldiy. At 12Oc 804 of the eggs dled durlng the two f ~ r s t days of the experi~ent, whlle 100% of the eggs ac id0, 16O and 1 8 O ~ dled wlthln the same period.
Flg. 6 shows the rriortality wrth increasrqg t~mneratures for the eggs exposed from stage 1SP. : hrgber rnortalrty was
Fig. 3. Egg development rate in different constant ternpera- tures from the gastrula stage (IbB) and onwards. H: hatching begins.
observed at 8Oc than in 6O and lo°C. This was due to an increased mortality between the second and fourth day at ~ O C .
A similar tendency was observed after the third day at 12 0
and 14Oc, giving a higher total mortality at 12Oc. At 16' and 18Oc all the eggs died within three and two days respec- tively. The experiments with eggs exposed from 3 8 at 14 and 0
16Oc were, as earlier mentioned, terminated before 100%
mortality (Fig. 7). The mortality until hatching was similar and negligible for the temperatures 6O-12OC. After hatching had started the mortality increased with increasing tempera- ture due 50 starvation. At 14' and 16Oc the mortality was considerably higher prior to hatching than at the lower temperatures. After hatching the mortality increased rapid- ly. At 1 8 O ~ all the eggs died within three days.
t ALL DEAD
5
10D A Y S
Fig. 4. Egg development rate in different constant tempera- tures from stage 3 5 and onwards. H: hatching begins.
D A Y S
Fig. 5. Egg and larval mortality in the experiments where the eggs were exposed to different constant temperatures from the first blastula stage (laa).
I0 15 DAYS
F i g . 6 . Egg a n d l a r v a l mortality i n t h e e x p e r i m e n t w h e r e t h e e g g s w e r e e x p o s e d t o d i f f e r e n t c o n s t a n t t e m p e r a t u r e s from t h e g a s t r u l a s t a g e ( I b S ) and o n w a r d s .
F l g . 7 . Egg and l a r v a l r n o r t a l r r y r n t h e experiments where t h e e g g s w e r e e x p o s e d t o d r f f e r e n t c o n s t a n t t e m p e r a t u r e s f r o m s t a g e 3 8 .
M o r t a l i t y i n d i f f e r e n t d e v e l o p m e n t s t a g e s
O n l y sn?a! l d i f f e r e n c e s i n morta1.it-y i n t h e d i f f e r e n t d e v e l o p m e n t s t a g e s were o b s e r v e d a t
e0
and I O O C f o r t h e e g g s e x p o s e d from s t a g e law ( F i g . 8 ) . A t t h e s e t e m p e r a t u r e s t h e mortality i n c r e a s e d a f t e r s t a g e l a v , an6 l u s t b e f o r e h a t c h -DEVELOPMENT STAGES
F l g . 8. Mor~allty in the different development stages for
eggs erposed to drfferent constant temperatures from the frrsr blastula stage (lan)
.
rng. A r 12OC the mortallty was high rn the stages up to 23 and rqe mortallty <?as low u ~ t l l che eggs had natched. All the eggs &led wltnout any further developrnert at 14 o
,
16O and iFJoc.Only small aifferences were observed at ~ ~ - for the 1 4 ~ ~ eggs erposed fron IbB (Fzg. 9). The mortalrty increased cteadily at these temperatures u ~ t r l 10O"oatchlnq. None of the 3evelopmencai stages seemed co be more affected by the temperatures Eo-i4"~ than others. However, at 16O and 18OC 100% mortalzty was observed d-urlng stages 1bB - 2 v .
F;s. L0 demonstrates the aortalrty In alfferert deveiop- mental sLages for eggs exposed to he experimental tevpera- tures from stage 3 P . The mortalrty was low at temperatures
~ ~ - for all stages. 1 2 ~ ~ Ft che lowrest temperatures the rorrallty r~creased sl~gnzly durrqg tatc~lng. At 14O and 1 6 O ~ the mortality was higher and similarly the mortality increased during hatching. At lgoc all the eggs died during
Ibplby 2 a 2 p 2 y 2 b 30 3 8 3 y L a L e H 5 0 100°/0 DEVELOPMENT STAGES
Fig. 9. Mortality in the different development stages eggs exposed t o different constant temperatures from gastrula stage (IbB)
.
for the
DEVELOPMENT STAGES
Fig. 10. Mortality in the different development stages for eggs exposed t o different constant temperatures from the stage 38.
Fig. 11. Mortality of larvae exposed to different constant temperatures from an age of one day.
Larval mortality
Tne larvae were hatched at 6OC and transferred when one day old to the experrmental temperatures. The morcalrty wlth t-ime 1s shown rn F-ig. 11. At al! temperatures, except 1 8 O ~ , the mortality was rather low untll starvation started. At 18OC 609 of the larvae died durrng tne first 2ay a n 2 all of -hem \?ere dead ~y the fifrh day. As demonstratpd r n Table I the resorpcrop rate of the yolk sac Increased wrth increasrng temperature. At ~ O - I O O C tbe yolk sac seemed to lasc for =he same perrod, three days. T h ~ s ss probably due to a dally observation ~ncerval, vzhich w ~ l l mask dlf f erences less than one day. At 18OC the yolk sac lasted only one day. The perrod after yolk sac resorpxlon, and un-ill the nortallty sncreased heavlly due to starvatron, was much shorter ac hlqher cenperatures t h a ~ low ones. At &"C and l 8 O ~ tills period lasted for e-ight and one day respectively. Some of the eggs whlch hatched resulted rn deformed larvae. hs shown
TABLE 1
The yolk sac resorption rate and the period of low mortality after yolk sac resorption in the different experimental temperatures.
Number of days Toe
wlth yolk sac wlrhout yolk sac and wlch lo~i rnortallty
rn Frg. 12 lust a few of the larvae hatched rn 6°-100~ were deformed, wilrle the number rncreased rather drastrcally at the temperatures above 1ooC. A slmllar trend was observed for the survlval rate of the larvae. The survlval was much better at temperatures below 1 2 O ~ than above (Flg. 12)
.
Thesurvlval rate and percentage of abnormal larvae were slrilar whether rhe eggs were exposed to he experrmental tempera- tures In stages 1be or 36. The percentage of abnormal ;arvae was also slmllar for the larvae from the eggs exposed to the dlf ferent temperatures fron development stage lau. However, tbe survlval rate was much lower even for tbe experrnental temperatures from later development stage5. The survxval rate was also much lower 11. thrs experrment for the tempe- ratures below 1 2 O ~ than ~t was for Larvae frow eggs exposed to the experlmevtal temperatures at later development srages.
Thls result 1s drffrculc to explarq but rs possrbly due to an experiaental art~Lact.
TEMPERATURE
Frg. 12. Percentage of abnormai (solld lrne) and survlvlng larvae (dotted irne) In d~fferent constant temperat~res. 1.
Larvae from eggs exposed from scage l a n , 2. Larvae from eggs exposed from stage IbB, 3. Larvae from eggs exposed from stage 3 8 .
Eggs and larvae exposed to temperature shock
7rg. 13 demonstrates that a temperature shock of 15 mln wlth hT of 10 deg C had no effect on the eggs rn stage laa.
In thrs case the nortallty 1 n the control group was even hxgher -;ban I n the group grrren the shock. The eggs whlch were grven the shock In stage IbB resulted rn an rricreased mortality of only about 10%. The treatment had no effect on eggs rn stage 3 8 . The percentage of abnormal larvae were low rn the three experiments, varyrng between 6% ana 8% In both the shock experrments and the control groups. However, for the larvae toe rmmedlate effect was an ~ncreased mortal-tl of aaout 2 0 % .
-
CONTROL- - - - S H O C K
DAYS
Flg. 13. Mortalrry rn the control lsolrd l r ~ e i and the temperatcre shock experlme~ts ( d o t ~ e d llnel. 1. Eggs exposed to temperature s b o c ~ ln srage iaa, 2. Eggs exposed to temperature shock ln stage IbB, 3. Eggs exposed to temperature shock In sEage 3 5 , 4. Newly hatched larvae exposed to temperature shock.
DISCUSSION
The hlological efEect of the temperature wrll bary wrth varylng sallnsty (Rlnne, 1 9 6 3 ) . Westerrlhagen (1470) demon- strated bat b o t i i tempera~kre and salinlry could change the mortality rare aqd the rncubatlon perrod of plarce, flounder and cod-eggs. hccordlng to tiolliday and Blaxter (i960j rhe
~ n c ~ b a t l o n perloa of herrlng eggs sas also rnfluenced b: tne salinity. In the experlmelts described rn thrs paper the sallnrty was almost constant, about 35O/00 durrng the experl- mental perrod. Therefore the observed effect of the terpera- ture on eggs and larvae 1s really a covbrned efzecr of varylng temperature and constant sallnlty.
The main trend in the different experiments was an in- crease of developmental rate with increasing temperature.
The incubation period of eggs which were exposed to 12OC from stage laa and lb6 was about 35% shorter than observed at 6OC.
A similar increase in developmental rate between 6'~ and 12Oc was also observed for the North Sea cod by Thompson and Riley (19811, and plaice and herring from the Norwegian Skagerrak Coast by Danielssen and Iversen (1974). By increasing the temperature above 12°-140~ the developmental rate did not increase in the same order as increasing the temperature from 6'~ to 12Oc. A similar effect of retardation in development by increasing the temperature above a certain level was observed for mackerel by Worley (1933) and for cod and plaice by Bonnet (1939) and Westernhagen (1970).
A rather high mortality was observed during the first two days for the eggs exposed from stage laa. This was probably caused by a combination of handling, natural mortality and that many eggs were possibly unfertilized. As observed by Laurence and Rogers (1976) no significant differences in mortality rates during the incubation period were observed in the temperature range up to 12 C. In all the experiments the 0
mortality increased drastically for the temperatures above 12Oc. However, this increase in mortality was less when the eggs were exposed to the temperatures later in the develop- ment. This was also observed for plaice eggs (Danielssen and Iversen, 1974).
The resorption of the larval yolk sac increased with increasing temperature. Only small differences in mortality during the yolk sac stage were observed when the larvae were exposed to temperatures between 6O and 16OC. However, at 18OC the mortality increased drastically. Experiments with newly hatched plaice and herring larvae from the same area (Danielssen and Iversen, 1.c.) demonstrated that the yolk sac of the cod larvae was resorbed faster than for these species.
A similar tendency was observed for the length of the period after the resorbtion of the yolk sac and until the larvae died due to starvation. The extension of this period was similar for plaice and herring, but shorter for cod. At 6 @ ~
and le°C the drffereace was observed to be approxrmately 10%
and 80% respecrrvely,
Abnormal larvae were oPserved rr all the experrments whether the eggs were exposed to the hlgher temperatures early or late In the development. The number of abnormal larvae was hrgh ac temperacures where mortallrv was h ~ g h , and low at those ~emperatures whrch gave low rnortallty. The number of abnormal larvae Increased consrderably at tempera- tures above 1 0 O ~ . Laurence and Rogers (1976) concluded that abnormalrty In cod larvae was Independent of temperature up to 1 2 O ~ . Thelr experlments were carrled out wrth cod from the east coast of the Unrted States, and that 1s probably the reason for thls difference. They also observed a hlqher number of abnormal larvae In the temperature range 6-looc thar was observed IP the preseot materral. T h ~ s could be due to both genetlc dlfferences and that thelr experlments were carrrea out In a closed water system.
The remperature shock of AT=lO deg C seemed ro have lrttle effect on the eggs and lariae. In t*+o cases, egqs rn srage lan and larvae, che lnmedzate effect was an Increase rn mortalr-cy by about 10% and 208 respectrvely. However, no effect was observed sn the other experrments. In the experl- ments wltb 3 8 eggs che mortality was 10% lower than rn the control group. Plalce eggs and iarbae treated the sanw way dra not seen to be affected (Iversen and Danrelssen, 1977).
Srmriar experrments pave neen carrlea out on drfferent frsh larvac fro? the east ccasr of Unlted States. r%ese experr- ments demoqstrated t h a ~ a ATO of 12 deg C for 46 mrn had no srgnsf-cant effect (Hoss, Hettler and Cosrow, 19741
.
Marcy(L9731 :nvest,gaced some fresh warer 'zsE- ia~i.-ae ac a riric1ear poher pianr. Ife o~served that GO-100% of rhc larvae dred -?hen thev passec throug% rhe coolrng system and t%e drscharge caval of tbe power plant. About 809 of the mortalsry was due to rnerqan~cal ctress, &pile tbc other 20" gas attributes to
n e i ~ snocr r ~ ~r-trp-%or d 1 a W - ? q n tenpe-l'ure
Chzs rs f o some ertenf supnortea b: rhr- present Ln~=est~qatlo-
i , h l c ? In two cases deponsrrareo an ~ncreased mortalrty of 10%
a n d 2 0 % f o r e g g s i n s t a g e l a a a n d l a r v a e e x p o s e d t o a LT=lQ d e g C *
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