Introduct ion to some f i sh spec ies

in the F innish Arct ic

Prepared fo r the Ca t ch and Keep

exh ib i t i on a t the A rc t i c Cen t re

BURBOT(Lota lota)

Appearance

Burbot has a typical appearance

of a species l iving at the bottom

of a lake: the front of the body is

almost round in cross-section but

the back is flattened, and its head

is f lat and broad. It seems soft

skinned because of its tiny, round

scales. The fin bones are soft. It

is most commonly brown, but also

greenish and almost black burbot

ex is t . The sk in pat tern i s l i ke

marble wi th b lack f igures on a

brown foundation. Under the jaw,

burbot has one lone ly whisker,

which is actual ly a sensory hair.

Its mouth is b ig and f i l led with

tiny, hardly visible teeth. On the

back bu rbo t have two do r sa l

fins,the posterior of which is very

long. Its caudal f in is separate

and round.

Burbot is normally 35-60 cm long

and weighs 0.4-3 kg. The biggest

burbot caught in Finland was from

Lake Pyhäjärvi, in the Province of

Ou lu , i t we ighed 15.5 kg . In

Alaska there are rumours of burbot

weighing over 30 kg and in Siberia

they te l l about 25-30 kg g iant

burbot. But maybe they did not

Surroundings

The most important requirement

i n a bu rbo t ' s env i r onment i s

temperature: during the summer

season i t prefers 4-12 degrees

Celsius. Big individuals thrive in

co ld water and therefore they

main ly l i ve in the co ld , lower

layers of lakes where the water is

s t r ong l y l aye red . Th i s i s t he

reason why burbot rarely l ive in

sma l l l akes . On the cont ra ry,

however, burbot fry and young

Nourishment

In winter burbot l ive in shal low

water and in spring move near to

c oa s t s i n o r d e r t o f e a s t o n

spawning fishes. When the water

gets warmer, these 'sl imy Sams'

return to deeper basins to spend

get the difference between a pound

a n d a k i l o g r a m r i g h t ( ? ! ) .

An over-10-year-old burbot is rare.

Nevertheless, o ld ies have been

found in Utsjoki, Finland (20 years

old) and in North America. The

oldest Alaskan female was 24 years

of age and 97 cm long. In Russia

two 25 -yea r - o l d g i a n t s we r e

caught, one weighed 7.8 kg and

the other 11.2 kg. All big burbot

are females. The males do not

u sua l l y g e t b i g ge r t h an f i v e

kilograms. Unlike other fish, burbot

also grow during the winter, which

is very logical s ince the f ish is

more ac t ive in w in te r than in

fish spend their whole summer in

warm and shal low coasts where

they f ind lots o f nour ishment.

The other restrictive factor is pH

l e v e l : r e p r o d u c t i o n i s n o t

successful if the pH level is less

than f ive. Burbot is sensit ive to

polluted water. As a species living

and reproducing in the basal i t

r equ i res a l o t o f oxygen and

the r e f o r e su f f e r s a l o t f r om

pollution of lakes, especially the

bottom layers.

Burbot is a very local f ish: the

l o n g e s t m i g r a t i o n s a r e t h e

migration to the breeding ground

and changing the summer basin.

Usual ly these migrations do not

exceed distances bigger than a

couple of tens of kilometers. The

longest migration noted in Finland

was 50 km.

Spreading area

Reproduction

The spec ia l i ty o f burbot is the

breeding season in the middle of

the winter, from February - March

when most an imals s leep. The

changes between the years are

rare. However the breeding season

is claimed to be shorter in cold,

snowy winters than in warmer

per iods with less snow. Burbot

reach sexual matur i ty from 2-7

years of age.

The breeding grounds are situated

3 meters deep, in sand, gravel or

mud bottom. Often there are some

small rocks as wel l . Many t imes

burbot come to spawn in streams,

whe r e t h ey move a l r e ady i n

Sep tember - December. A s a

r e m i n d e r o f t h e c l a s s o f

Gadiformes and their origins in the

sea (cod spawn f loats near the

surface) burbot have a tiny drop

of oil in each egg which is enough

to make the egg f loat r ight

not ions , however, do not

q u i t e c r e a t e t h e r i g h t

p e r s p e c t i v e . Bu r bo t e a t

spawn as well as their own

ones and burbot is a prey for

other fishes.

the summer there . Dur ing the

summer adu l t f i sh ha rd ly ea t

anything, they spend the summer

l y i ng and r e s t i ng . When t he

autumn comes burbot get more

act ive in f ind ing nour ishment .

Du r i n g t h e w i n t e r p e r i o d o f

darkness burbot are active during

the day too.

Burbot find nourishment by using

its sense of smell, touch and taste.

The tactile nerves are situated on

a whisker, called a barbell, as well

as in the longest abdominal f in

bone. In dark water its sense of

sight is practically useless because

the eyes of burbot are usual ly

bl inded by a parasit ic cataract.

This blindness is normally caused

b y a m a g g o t o f t r e m a t o d e

(D ipo los tomum spac thaceum) .

Like most fish, as a fry burbot live

on animal plankton. When it is 1-

2 cm long i t moves f rom the

surface to near the bottom. Basal

animals are the main nourishment

until the fish reaches 20 cm, then

it starts eating small fish as well

and changes s lowly to a f ish of

prey. The amount of basal animals

on the menu decreases, but even

the biggest fish sti l l occasionally

ea t t hem. In l akes t he mos t

important prey are European cisco,

ru f f, smel t , perch and mi l le r ' s

thumb. But burbot do not get picky

even when facing a hibernat ing

frog: the frog too ends up in its

mouth to be minced by i ts t iny

teeth. Bourbot have a big head

and mouth so even a big fish fits

in easily. Normally, however, the

size of prey is only 20-30% of the

predator's size. Sometimes burbot

can get greedy and eat more than

it can digest. As a slow fish it must

ea t eve r y th i ng t ha t i t f i nd s .

Burbot have a rather unpleasant

reputation as a spawn eater - there

are stories about a 4 kg burbot

having eaten 1.5 kg of spawn of

lavaret and European cisco. These

up from the bottom of the lake.

For one ki logram of weight each

female carries 500 000 -600 000

eggs. The fry peel off at the same

time as the ice melts on the lakes.

The fry aim to the surface r ight

after to get some air in their swim

bladder. At the beginning, fry live

on their vitalline sac, but already

when 10 mm long they start eating

animal plankton.

Appearance

In the coastal areas and inland

lakes trout are often confused with

salmon. These two species look

very similar. In addition there can

be a g rea t dea l o f va r i e ty i n

appearance among the species.

Trout usual ly have lots of dark

spots below the lateral l ine while

salmon hardly have any. Trout is

a l so more b lo tched above the

lateral l ine than salmon. Trout's

f luke part is normally thick and

ful l boled. The caudal f in is not

clearly separated from the tail. On

the contrary, salmon have a fluke

pa r t t ha t i s t h i n and t ape r s

towards the ta i l f i n . The l i ne

between the caludal fin and tail is

very visible. The trout's caudal fin

is a lmost s t ra ight and wi thout

cuts, whereas salmon have plenty

of them. Trout have 14-19 scales

between the lateral l ine and f in

behind the dorsal f in. The upper

jaw reaches a bit behind the eye.

Trout in lakes, seas and rivers are

usual ly s i lver co lour, but t rout

living in streams and small rivers

are browner and more blotched.

In addition to black spots on the

sides they also often have red and

rus ty- red spo t s . The f i n s a re

L i fe cyc l e and su r round i ngs

Trout is a migrant, but does not

always leave the birth river. Part

of the population stays in the birth

r iver and par t becomes brown

t rou t . M ig ra t i ng t rou t do no t

bother to make long migrat ions

like salmon do. Sometimes, during

their migration they might even

return to their birth river to find

some young insects and other

nutrition floating on the surface.

After eating enough they return

to the lake or sea. In the sea,

trout usual ly migrate no further

that tens of kilometres of distance

from the coast. Even the longest

migrations reach no further than

a couple of hundred of kilometres

from the birth river.

Despi te the fact that in costa l

normally spotless but the dorsal

and tail fins may have some faintly

visible dark spots.

Fry l iving in r ivers are dark and

spotted. On both sides they have

10-12 unc l ea r da rk b l o t ches .

Among the dark spots there might

be a few spots surrounded by a

clear, red ring. Fry living in rivers

have spotted fins. The differences

between trout and salmon fry are

very small: trout have more spots

on the operculum and red spots

m a y h a v e a c l e a r e d g i n g .

Like with salmonoids in general,

the trout's growing speed depends

st rong ly on the env i ronmenta l

circumstances. River fry grow quite

slowly. During the f irst summer

f ry reach 10 cm of length but

during the two following years it

only grows 4 -6 cm more. In lakes

and seas, trout grow faster the

further south they live. Sea trout

normal ly reach 40 cm in length

and a weight of 1-3 kg during their

second year in the sea. After the

third year they are approximately

50-70 cm long and weigh 3-5 kg.

The biggest trout ever caught in

Finland was in the Gulf of Finland

in 1977. It was 104 cm long and

weighed 16.2 kg. There are some

stories about bigger trout, even

over-20 kg ones, but most l ikely

these fish were salmon.

Normally the bigger f ish species

reach a h i ghe r age than the

smaller ones. Trout, however, is a

relatively short-aged species: the

oldest trout caught in Finland was

a 12-year-old trout caught from

the Juutua River.

TROUT(Salmo trutta)

Spreading area

Nourishment

The f irst nutrient of small fry is

t h e v i t e l l i n e s a c . W h e n i t

disappears trout f irst use animal

plankton found in rapids and later

insects floating on the current and

grubs and shellf ish l iving on the

bottom. Maggots of midges are the

favourite meal of trout of all ages.

The bigger grubs of caddisflies and

areas trout have lots of space and

possibility to migrate, they rarely

go far from their place of birth or

the spot they were stocked to.

They s tay c lose to the coast ,

although they might strol l quite

far along it. When summer turns

to autumn trout are caught by an

invincible desire to return to their

place of birth, the very same river

or rapids were they began their

l ives and journey. The hormones

of the f ish start changing their

appearance: a ma le ready to

spawn gets the colourful skin tone

and hook-l ike jaw typical to al l

sa lmonoids. The age of sexual

maturity depends strongly of the

growth and the length of the fry

period of the fish. The youngest

spawning f ishes are normal ly 4

years old. But for example in Lake

Inari the f ish that spawn are no

younger than 6-7 years of age.

The spawn migration starts early

i n t h e s u m m e r a n d l a s t s

throughout the autumn.

Trout a lways breed in running

water: in rivers between two lakes

or streams and rapids above lakes.

However, some populat ions are

known to spawn in the r ivers

below a lake area as well. Trout

are found only in lakes that are

cool enough and contain lots of

oxygen even during the summer

season. This means big lakes and

waterways, streams and r ivers.

The female digs the nest in gravel

in the place where the speed of

the current is approximately 25-

40cm/s and the r iver is 20-100

cm deep. Trout spawn in a b i t

slower and shallower water than

its cousin salmon.

Fry hatch out in the spring and

make the i r way up f r om the

gravely bottom when they have

lost their vitel l ine sac. Each fry

has its own territory which grows

bigger as the fry grows. The size

of the territory also depends on

the quality of it: the more hiding

poss i b i l i t i e s , t he sma l l e r the

terr itory. River fry stay at the

territory for 2-5 years, but in

northern parts of the country

fry can stay in rivers for up

to 7 years. The amount of fry

years spent in a river is not

as regular as with salmon.

There might even be lots of

variation with the fry l iving

in the same river. The age of

wander lus t co r re la tes w i th

growth: the faster a fry grows,

the sooner i t leaves the b i r th

environment.

Young trout live mainly near shores

and estuaries. They spend their

f i rst year in re lat ive ly low and

slow-moving water where they can

e a s i l y f i n d s h e l t e r - p r ov i d i n g

vegetation. When they grow bigger

they start favour ing cooler and

deeper water and avoiding areas

with lots of vegetation. Trout like

deep lakes, inlets and other places

with strong currents and lots of

oxygen.

A fry leaving for its first migration

is about 20 cm long. Trout change

l i ke sa lmon: they l oose the i r

terr i tor ia l i ty and star t forming

shoa l s . The i r co l ou r becomes

silvery.

d r a g o n f l i e s b e c o m e m o r e

important on the menu as fry grow

bigger.

Fry start eating small f ish when

they are about 20 cm long. The

amount o f f i sh nutr ient grows

whi le the trout get b igger. The

most important prey are European

cisco, small whitefish, smelt, perch

and nine-spined stickleback. Sea

trout mainly eat Balt ic herr ing,

sprat and three-spined stickleback.

Trout in costal areas also eat black

c lams, sand lances, perch and

eelpout.

Appearance

Arctic char is probably the most

beautiful fish living in Finland. It

is c lear ly a darker co lour than

salmon or trout. Its appearance

varies a great deal according to

ecological circumstances. The back

i s da rk and s ides a re b rown,

greenish or sometimes even fair.

On the sides the f ish has red or

pink blotches. Its stomach can be

red, ye l low or somet imes even

white. Small Arctic char l iving in

Lap l and a lways have a wh i t e

stomach. The fronts of the anal

and abdominal fins are white and

the caudal f in is dark. Its mouth

reaches behind the eyes and has

lots of teeth. Its scales are small

and on the lateral l ine there are

normally 123-145 of them. Spots

on the sides are white.

Small Arctic char are usually 10-

30 cm long and weigh under 0,5.

Big Arctic char are 35-60 cm long

and weigh 1-3 kg. The div is ion

acco rd ing to s i ze revea l s b i g

differences in growing speed even

within the fish living in the same

lake: Big Arctic char living in Lake

Surroundings

Arctic char is the legendary f ish

d o m i n a t i n g c o l d a n d b a r r e n

northern waters. It is successful

even where other species can no

longer survive. The coldness of

wa te r i s v i t a l t o A r c t i c cha r

be cau se i t s va s cu l a r s y s t em

requires a temperature below 15-

16 C to be able to successful ly

transport oxygen. The surrounding

water must contain 5 mg of oxygen

per litre. Arctic char is very fragile

when it comes to acidity. It does

not l ive in lakes with a pH value

of less than 6.2. In southern lakes,

Arct ic char can only surv ive in

dark and cold basins. On the other

hand, it is successful in relatively

h u m u s wa t e r s y s t e m s . L a ke

bottoms are usually sand, gravel

or stones.

Nourishment

Arct ic char l ive in areas where

there is continually a shortage of

Inari reach 34 cm by five years of

age and small Arctic char only 25

cm by the same age. When f ish

grow o lder the d i f ference gets

b i g g e r. T h e g r o w t h i s n o t

genet i ca l l y de f ined. There are

examples o f sma l l A rc t i c char

growing b igger when they are

removed to another area or when

t h e p o p u l a t i o n d e c r e a s e s .

The biggest Arctic char ever caught

in Finland weighed 9 kg. It was

caught on Lake Sevet t i järv i in

1917. The Arctic char living in the

fell area usually weigh 200-500 kg

but on the contrary, the Arctic char

living in big lakes and specialising

in eat ing pygmy white f ish can

easi ly reach 1-2 kg. The Arct ic

char living in the sea grow bigger

because of better nourishment: In

Canada the biggest arctic char ever

caught was 16 kg. In Norway fish

between 10-12 kg a re caught

regu lar ly. They c la im that the

biggest one caught in Spitzbergen

was 15 kg and 25 years old and a

31-year-o ld f i sh was caught in

Svalbard. The Arct ic char l ives

longer than salmon or trout: easily

15 - 18 years. The oldest one in

Finland, a 17-year-old f ish, was

caught in Lake Inari.

ARCTICC H A R(Salvel inus alpinus)

Spreading area

Reproduction

Normally the cold-blooded Arctic

char get agitated when the Arctic

night is the darkest and freezing

w inds s ta r t m ix ing l akes and

rivers. In September to November,

when the wa te r i s abou t 3 -6

degrees warm the temperature

a c t i v a t e s h o r m o n e s o f

reproduction. Arct ic char spawn

in shallow coasts near gravel and

stony beaches where the depth is

between 3-5 m, occasionally Arctic

char are known to spawn even

at10 m of depth. Small Arctic char

somet imes spawn i n s t r eams

nutrients and therefore the f ish

have become a very multifaceted

eater. Almost all the nourishment

available is good enough and they

are even able to change their diet

if needed. After the vitel l ine sac

is gone, a f ry 's f i rst nour ishes

itsel f with water f leas, f ish-l ice

and muggs of fly and black fly. At

the end of their first summer fry

also eat insects on the surface,

shells, shellfish and barnacles on

the bottom. The young Arctic char

l ive on small animals during the

f i rst 4-6 years. After that they

star t catch ing other f i sh . F ish

nou r i s hmen t s t a r s be i ng t he

dominating part of the diet when

the f ish reaches a size of 25-10

cm. The most important prey are

small white wish, European cisco,

nine-spined stickleback and other

small fish.

In some lakes in Norway the only

nour ishment for Arct i c char i s

animal plankton and some bottom-

feeding animals. On this diet Arctic

char cannot grow big and the fish

are rather modest in size. On the

contrary, the big Arctic char living

in big lakes are predators during

most of their l ife. In small lakes,

A r c t i c c ha r u se a l l f o rms o f

nutr ients, in bigger lakes there

might be n iches spec ia l i sed in

di f ferent k inds of a l imentat ion.

i n s t e a d o f l a k e s . T h e

migrating Arctic char that live

in the Teno River usually spawn

in very cold tributaries that are

too co ld fo r Sa lmon or Trout .

Spawning starts when the sun sets

and males start defending their

terr itor ies. They threaten each

other by strewing their f ins and

opening their mouth or nibbl ing

one another. The fema les ge t

aggressive as well, but soon males

accept them for the courtship. The

a c t o f s p a w n i n g i s a v e r y

complicated series of instinctive

behaviour. At the end the female

buries fertilised eggs on the gravel

with its tail. After spawning with

one female the male starts chasing

after another. The female stays

watching over the eggs for a few

days.

The Arctic char ready to spawn is

a magnificent f ish: the colour of

the s tomach i s da rk r ed and

orange. Its back is dark blue or

green. The sides are covered with

yel low or red spots and the f ins

are milky white. The male might

get a hook-like chin as salmon do.

The females look more modest

than the males.

Arctic char normally reach sexual

maturity at the age of 3-6 years,

but fish spawning might vary a lot

when i t comes to s i ze . Some

populations spawn already when

they are 10-15 cm long and other

faster growing ones when they

reach 35-45 cm. A female that

weighs 1 kg carries 2 000 - 4 000

eggs.

The eggs are developed in the

gravel during the winter and the

fry peel of f when the ice melts

away. During the very first months

of life the fry live in shallow water,

but then they move to deeper

waters.

Appearance

The species Atlantic salmon is divided

into two ecological niches: the salmon

growing in the sea and freshwater trout

that spends its youth in lakes. During

the sea or freshwater period, young

salmon are silver coloured on the sides,

dark grey on the back and white on the

stomach. On the back they have some

dark spots. The mouth never reaches

beyond the back of the eye. The tail is

skinny and the tail fin has a cutting (cf.

trout). The operculum rarely has spots.

In between the lateral line and the fin

behind the dorsal f in there are 11-15

scales.

Salmon ready to spawn lose their silver

co lour and turn to a grey-green or

brownish colour. More spots also appear

underneath the lateral l ine; some fish

can even be entirely black. The cutting

on the tail fin is hardly visible and the

upper jaw can reach behind the eye.

Most of the confusion between trout

and salmon has been caused by the

male salmon caught in sea during the

middle of the breeding season. At that

t ime they m igh t a l so have a r ed

stomach and trout-l ike hook on their

chin.

The back of a salmon fry is brown and

the sides are covered by lines formed

by dark spots. Near the lateral l ine it

has some black spots as well. The only

visible resemblance with an adult fish

i s t he f i n beh i nd t he do r sa l f i n .

The fry grow up rather s lowly. After

two summers they are approximately

11 cm long and by the end of the fourth

summer 16 cm. If a fry stays in the

L i fe cyc l e and su r round ings

At l an t i c s a lmon l i ve i n pu re and

oxygen-r ich water systems and can

cope with a very strong current. The

sea migration can be 1-3 years long.

In seas, salmon live in open water and

come nea r t o c o a s t s o n l y when

migrating to their breeding grounds.

When a fish achieves sexual maturity

and gets strong enough, it returns to

i ts r iver of b ir th in order to spawn

there. The ind iv idua ls that do the

longest migrat ion return the oldest.

ATLANTICS A L M O N(Salmo salar)

rapids for a f i fth year it wi l l grow to

be19 cm l ong . A t the end o f the

freshwater period, the fry prepare to

move to sea, both physiologically and

appearance-wise. The spots disappear

and sides turn si lvery. The back gets

dark and the tail longer.

In the sea, fish grow faster because of

the different nutrients. After a year, a

salmon weighs about 1-2 kg, in two

years 4-6 kg and in three years 6-12

kg. If a salmon survives the fifth year

in the sea it weighs more than 20 kg.

Usual ly al l the big salmon are male,

females do not grow qui te as fast .

The sa lmon caught in the sea are

normally about 1 m long and weigh 4-

20 kg. The biggest one ever caught in

Finland was 43 kg and it was caught in

Tornio River. The biggest prey in North

Amer i ca we ighed 25-30 kg and in

Estonia 38 kg. In Norway and Sweden

there are many notes about salmon

weighing more than 30 kg and in the

British Isles of fish less than 30 kg of

weight.

The return migration starts in spring

soon after the icy cover melts. It is

strongest in June and continues until

the end of the month. Despite various

theories about gravity, sea currents,

magnetic f ields, diurnal rhythms and

planets, there is still no certainty about

the way the fish manage to orientate

their way back. In any case, when the

fish get close enough to use their sense

of smell they persistently aim to the

river of birth. Salmon do not give up

even when facing the most impossible

obstacles. Some might call jumping at

a dam of a hydropower station stupid,

but their instincts are so strong they

cannot resist them. In the river Atlantic

sa lmon no longer eat; they at tack

fishing tackle only because of a reflex

o r s t r o n g t e r r i t o r i a l b e h a v i o u r.

Return migration is a natural way to

l i m i t t h e n u m b e r o f s p a w n i n g

individuals and therefore a means not

to exceed a r iver ' s env i ronmenta l

capacity. A big river can have a bigger

population than a small one. Migration

in itself is considered as the species'

way to maintain the population as big

as possible.

September to November is the actual

spawning season. The breeding ground

is usually situated in a main riverbed

with a gravel bottom and little rocks.

Typically, salmon spawn in 0.3 -2 m of

depth where the speed of the current

is 45-55 cm/s. A female chooses the

spot where it digs a nest for the eggs

with i ts ta i l . The eggs are big: the

diameter is 6-7 mm. A female of 10

kg carries approximately 10 000 eggs.

Spawn and sperm are spread almost

simultaneously, after this the fertilised

Spreading areaMigration

Atlantic salmon is a typical migrant.

The salmon living in the Baltic Sea does

not normal ly pass the s t ra i ts near

Denmark, and stays in the Baltic Sea.

However, some exceptions are known:

the longest migration documented was

from Bothnian Bay to the west coast of

Greenland which makes over a 5000-

km journey. The Bothnian Bay is rather

barren surroundings so for that reason

salmon has to migrate to f ind better

nourishment. In general, however, fish

l iv ing in the Ba l t i c Sea do shor ter

m ig ra t i ons than f i sh l i v i ng i n the

Atlantic. European and North American

salmon migrate to the same areas in

the North Atlantic. In seas west and

south of Greenland, f ishermen have

caught salmon marked in Canada, Great

Britain, France, Norway, Sweden and

the United States. From the Teno River,

Atlantic salmon usually migrate to the

North Atlantic or to the Arctic Ocean

north of Norway. Several f ish marked

in the Teno River have been caught in

shallow surroundings of Jan Mayen and

a r e a s e a s t o f G r e e n l a n d . T h e

surroundings of Iceland are not rich in

nour ishment so sa lmon rare ly s tay

there.

a n c e s t o r s h a v e d o n e f o r

thousands of years. Li fe is hard

and most o f the sa lmon d ie o f

hunge r o r e nd up b e c om i ng a

predator's prey.

Nourishment

The fry l iv ing in a r iver mainly eat

animal plankton, basal animals and the

insects and muggs f loat ing w i th a

current. After 1- 2 years of age fry

start eating fish eggs and other fry. On

the migration, a fry hardly thinks of

eat ing but i t might as wel l catch a

f loat ing insect or a crawl ing mugg.

Fry in the sea start eating small f ish,

shellfish, muggs and worms. When the

fry grow, fish become more dominant

on the menu as well; when the Atlantic

salmon is about 25-30 cm long other

fish become the most dominant part of

i ts diet. Salmon this big cannot eat

b ig f i sh bu t sma l l Ba l t i c he r r i ng ,

European cisco, smelt, sprat and three-

spined are well-nourishing prey. In the

Baltic Sea, Arctic salmon mainly gorge

on Baltic herring, sprat, three-spined,

sand l ances and she l l f i sh . In the

At lant i c Ocean, sa lmon eat lo ts o f

capelin and gadiform's fry.

spawn sinks to the gavel and the female

cont inues the journey up the r iver.

Males stay continuing their battle over

new females.

Some males reach sexual ly maturity

already before migrating to sea. These

agile youngsters are faster than clumsy

seacomers, but they easi ly lose the

actual territorial battles. For females

the period spent in the sea is necessary

because of the development of eggs.

Most of the salmon die off during the

hardships of the journey during the

next winter. Some individuals might

stay in the river for a winter especially

i f i t comes ear ly. In the w i ld , the

amount of fish spawning for a second

or the th ird t ime is less than 10%.

Despite of the massive death of the

adult f ish, l i fe goes on and new l i fe

develops in fish eggs lying in the gravel.

The water pouring slowly through the

sandy f loor br ings nutr ients to the

embryos and takes away the slag. In

January to February under the ice cover,

two black spots, the eyes, appear on

the egg. The fry watch winter turning

into spring: days get longer and the

ice cover melts away. It peels off from

April to June, breaking the egg easily.

It does not leave the gravel floor before

the vitel l ine sac has disappeared. By

that time it already looks likes a proper

fish and knows how to swim, which is

a good thing to know living in a river

that floods every spring.

Fry l ive a lone. A l ready in the f i rs t

summer they colonise a territory that

they defend against rivals. The territory

gets bigger as the fry grow. Territorial

behaviour sets limits to the amount of

fry growing in the same river. The river

period normally lasts 1-7 years, but

the further north the longer the f ish

stay in the r iver ( in Teno River 2-8

years). It has been estimated that one

of a 100 eggs manages to grow into a

f ish ready to migrate. Th is natura l

selection is very functional: different

populat ions have adjusted to the i r

environment in the best possible way.

A fry ready to migrate soon real ises

that his companions are anything but

unpleasant. Soon they form a shoal and

start their journey towards the unknown

sea. Migration starts during the spring

flood and happens mainly during the

night in order to avoid daytime dangers.

Despite the dangerous journey most of

the salmon survive until the mouth of

the river. After having recovered from

the shock caused by the salty water

they head to the open sea l ike their

Appearance

Whitefish is pure silver apart from

its dark back and mi lky whi te

stomach. All the fins are dark grey.

A small f in behind the dorsal f in

s h o w s t h a t i t b e l o n g s t o

Salmonoids. The head is small and

the body shut t l e shaped. The

mouth is small and toothless and

the upper ch in i s longer than

thelower one (cf. European cisco).

When i t comes to appearance,

d i f fe rent forms o f the spec ies

differ in the relative size of their

head and fins as well as the parts

of branchial arch. Some whitefish

living in Lapland's lakes are more

differentiated: sides are brown,

eyes are big, neck is hooked and

the meat i s so f te r than o ther

whi te f i sh 's . The d i f ferences in

branchial arch correlate with the

surroundings and the life cycle of

the fish. Whitefish of the northern

hemisphere i s a ve ry va r i an t

species: the different forms of the

species can d i f fer a great deal

par t i cu la r ly when i t comes to

g r o w t h , s i z e , n o u r i s h m e n t ,

appearance o r spawn ing even

within the fish living in the same

lake.

It is impossible to ful ly describe

the growth of whitefish because

Surroundings

The most important condition for

reproduct ion i s the amount o f

oxygen at the bottom of the lake.

A typical lake with a successful

whitef ish populat ion is a water

sys tem w i th sandy, g rave l o r

mora ine bot tom. I f success fu l

reproduction of the species is not

the a im, restocked populat ions

survive in small lakes and even

pond s a s l o ng a s t h e wa t e r

c o n t a i n s e n o u g h ox yg e n . I n

addit ion there must be a basin

deep and cold enough to help the

fish survive the warm periods of

summer. Whitefish is a cold-water

species and i t might even stop

growing as a consequence of water

temperatures being too warm in

summertime.

The migration of whitefish is also

very irregular. There are two kinds

of populat ions known: the ones

that migrate and the ones that do

not. The longest migrat ing sea

species is the Baltic whitefish; the

others migrate much less. In lakes

the migration is rather limited and

the longest migrat ions reach a

distance of only 30 km.

WHITEFISH(coregonus lavaretus)

even the f ish l iv ing in the very

same lake can grow di f ferent ly.

The same also goes for the same

fo rm o f t he spec i e s l i v i ng i n

different water systems. Normally

the size of a whitefish is 25-50 cm

and the weight 200-2000g. At the

end of the f irst summer a fry is

abou t 10 cm l ong . A f t e r tha t

dif ferences between populat ions

become visible. The most slowly

growing forms, l i ke the p igmy

populat ions in Lake Inari or the

ones living in the Gulf of Bothnia,

can grow old without ever getting

bigger than 25 cm and 150g. On

the other hand, Balt ic whitef ish

that l ive on the south coast can

easi ly reach a weight of 1 kg by

four years of age and by six years,

twice the size. Whitefish of 12 kg

have been caught two t imes in

Finland. The growth of the species

is defined by nourishment as well

as genetics.

Whitefish over 10 years of age are

occas iona l l y caught . They a re

r a t h e r r a r e b u t e x i s t i n a l l

populations. A few over 20-year-

old fish have been caught in some

small lakes of Lapland. In addition

a 378 g 37-year-old whitefish was

captured in 1990 in Lake Hauken,

Norway.

Spreading area

the sides.

Males are more anxious to

spawn and they arrive before

f e m a l e s t o t h e b r e e d i n g

g r o u n d . U n l i k e m o s t

Salmonoids, whitefish do not dig

a nest but drop the eggs in the

water and they sink to the bottom.

The sunken eggs are safe on the

gravel and predators can f i l l up

their stomachs with the eggs that

remain on the surface.

Sexual maturity varies as well. The

Balt ic whitefish males spawn for

their first time at 3-5 years of age

and females a year later. Some

populations in Lake Inari do not

become sexual ly mature before

they reach 5-7 years old. A female

ready to spawn carries 20 000 -

50 000 eggs per 1 kg of weight.

Fry peel off when the ice cover on

the lake breaks up and they start

eat ing an imal p lankton on the

shore. Fry in r iver also eat and

slowly drift down the river towards

the new surroundings, the lake or

the sea. By the autumn fry are 10-

12 cm long.

The populat ions that spawn in

rivers have declined because of

the treat ing of the breeding

g r o u n d s a n d h u m a n

a c t i o n l i m i t i n g t h e

migration routes. The

populations spawning

in lakes suffer most

from the restraining

o f waters sys tems.

Reproduction

Whitefish spawn in October when

autumn rains drop on the lake and

the trees change colour. But again

t h e r e a r e s o m e d i f f e r e n c e s

between populations even within

the same lake. The exact time of

s p a w n i n g i s d e f i n e d b y

temperature. Some populat ions

have their marital ceremony in the

lake and some swim up in the

river, but even the time and the

date can be different. Whitef ish

normally spawn in shallow water

near sandy and gravely lakesides.

Bu t aga i n , s ome popu l a t i ons

spawn over a ten-metre-deep spot

( in Lake Inar i even 15-20 m).

Du r i ng t h e s pawn i ng s ea son

whitefish get a few nodes on the

s ides. Most l ike ly these nodes

have a role in spawning rituals.

Probably they add sensit ivity to

Nourishment

When it comes to food, whitefish

are not picky at all although the

small, toothless mouth sets some

limits for the menu. Fry l ive on

animal plankton but already at 1-

2 years of age the diet includes

shrimp, barnacles, small shel ls,

and maggots. The bigger the fish

gets , the more dominant f i sh

becomes on the diet. When given

the chance, whitefish eagerly feast

on f ish eggs. They often catch

insects on the surface as well. In

t h e c o m p e t i t i o n o v e r f o o d

whitef ish is quite successful: i t

easily beats perch and Arctic char

but looses to i t s smal l cous in

European c isco. Therefore the

good f ishing years for whitef ish

a n d E u r o p e a n c i s c o r o t a t e .

The populat ions spec ia l i sed in

eating plankton normally grow big.

One excep t i on i s t he pygmy

population in Lake Inari.

A r k t i k u m 1 5 . 0 6 . 2 0 0 4 - 1 6 . 0 1 . 2 0 0 5

Fishmodels: Raimo PankkonenPhotographing of f ishmodels: Antti TenetzLayout: Ol l i HeikkinenSources from RKTL and CAFF