[ HELGOLANDER MEERESUNTERSUCHUNGEN Helgol/inder Meeresunters. 51, 191-196 (1997)
L e r n a e o c e r a b r a n c h i a l i s
(L., 1 7 6 7 ) o n c o d
i n B a l t i c w a t e r s
G. S u n d n e s I, J. Mork, P. S o l e m d a l 2 & K. Solerndal 2
The Royal N o r w e g i a n S o c i e t y of S c i e n c e s and L e t t e r s Foundation; 7013 Trondheim, N o r w a y
2Institute of M a r i n e Research, Bergen, N o r w a y
ABSTRACT: Field surveys have shown a limited distribution of L. branchialis in Baltic waters due to heterogenic salinity. The parasite is not suited as "natural" tagging of the cod population in these waters.
I N T R O D U C T I O N
T h e parasitic c o p e p o d Lernaeocera branchialis (L.) on cod in Nordic waters was d e s c r i b e d for the first time by Strom (1762).
T h e r e are two parasitic stages in the life cycle of L. branchiaBs. T h e first stage is f o u n d on species in several families (Sundnes, 1970). In the first period of d e v e l o p m e n t , the parasite goes t h r o u g h several d e v e l o p m e n t a l stages until c o p u l a t i o n takes place. After c o p u l a t i o n the f e m a l e swims freely until it attaches to the final host. O n l y the fe- m a l e has this s e c o n d stage of d e v e l o p m e n t . The m a l e dies after copulation.
This s e c o n d stage is m a i n l y f o u n d on g a d o i d fish, b u t also other fish families c a n be final hosts for L. branchialis (Kabata, 1958).
T h e m a t u r e female has easily d e t e c t a b l e "egg strings" (Fig. 1) w h i c h are s e g m e n t e d , e m b r y o s b e i n g c o n t i n u o u s l y r e l e a s e d from these.
T h e parasite has a p a t h o g e n i c effect on the cod that varies in degrees. T h e p a t h o g e - nic effect is d e p e n d e n t on the size of the fish as well as on ecological conditions in the specific cod p o p u l a t i o n [Sundnes, 1970; Kahn, 1994).
192 G. S u n d n e s J. Mork, P. S o l e m d a l & K. S o l e m d a l
Fig. 1. Cod infected with Lernaeocera branchialis (A) with developed "egg" strings
RESULTS A N D C O N C L U S I O N
D u r i n g a s u r v e y in Baltic w a t e r s in 1972 w i t h R. V. "Alkor" from the Institut for M e e - r e s k u n d e in Kiel, 2356 cod w e r e e x a m i n e d from 7 trawl stations (cf. Fig. 2 a n d Table 1). At t h e w e s t e r n m o s t station in the fished area, only o n e L e r n a e o c e r a b r a n c h i a l i s w a s f o u n d a m o n g 1081 cod. At this locality the salinity of the w a t e r was 24.5 %o. At t h e o t h e r t r a w l stations no p a r a s i t e s w e r e found. No salinity d a t a east of 15 E w e r e t a k e n on this survey. Arntz (1972) f o u n d t h e s a m e situation in Kiel bay w h e r e an i n f e c t i o n r a t e in cod of 0 . 1 % w a s found.
H e c o n c l u d e d his findings w e r e p o s s i b l e b e c a u s e of an inflow of salt w a t e r from the Kattegat. O u r finding of an i n f e c t i o n r a t e of 0 . 1 % at station 7 m u s t be c o n s i d e r e d to be a c o i n c i d e n c e .
Lernaeocera branchialis (L., 1767) o n c o d i n B a l t i c w a t e r s I 9 3 14 ~ 16" 18" 20 ~ 22 ~ 24"
59"
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)
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5 9 ~
9
0 ~
vI"
s s " ; .b ~
- 5 8 "
W E D E -. F I N L 4 N D
: ~ OLM I
5 6 " i
~ ~ . 5 6 ~
I .AND
I
5 5 ~ --,',--v~ t c ~,,~" , 5 5 "
1 4 " 1 6 " 1 8 " 2 0 ~ 2 2 4 ~
194 G. S u n d n e s , J. M o r k , P. S o l e m d a l & K. S o l e m d a l
P:
,4
9
{D
~ B ~ ~
Z Z Z Z Z Z
E ~
o .~
m ~ N
L e r n a e o c e r a b r a n c h i a l i s (L., 1767) o n c o d i n B a l t i c w a t e r s Table 2. Osmolality in cod off the Norrby Laboratory
195
Fish no. Sex Body l e n g t h m. Osm L. branchialis
(cm)
1 Female
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Male
62 382 0
59 382 0
67 338 0
76 316 0
68 357 0
73 289 0
73 329 0
56 346 0
59 333 0
62 365 0
61 288 0
61 356 0
56 368 0
59 310 0
55 355 0
56 354 0
79 307 0
66 368 0
64 312 0
57 360 0
72 316 0
53 331 0
41 346 0
61 354 0
58 37O 0
76 340 0
61 356 0
56 368 0
h a d a b n o r m a l g o n a d s a n d t h e o t h e r a l i v e r i n a p a t h o l o g i c a l c o n d i t i o n . T h i s m a y r e d u c e t h e i r a b i l i t y to h o l d s t a b l e o s m o l a l i t y .
1 9 6 G . S u n d n e s , J. M o r k , P. S o l e m d a l & K. S o l e m d a l
L I T E R A T U R E C I T E D
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Kiel B u c h t u n d s e i n e B e d e u t u n g als b i o l o g i s c h e M a r k i e r u n g . - A r c h . F i s c h W i s s . 23, 118-127.
K a b a t a , Z., 1958. Lernaeocera obtusa n. sp. Its b i o l o g y a n d its effect o n t h e h a d d o c k . - Mar. Res. 3,
1-26.
K h a n , R. A., 1994. P a r a s i t e s a s p o t e n t i a l p a t h o g e n s in a t l a n t i c cod m a r i c u l t u r e . - C . M . / I C E S , F 22,
1-5.
P a n i k k a r , N. K. & S p r o s t o n , N. G., 1941. O s m o t i c r e l a t i o n s of s o m e m e t a z o a n p a r a s i t e s . - P a r a s i t o -
l o g y 33, 2 1 4 - 2 2 3 .
S h e r m a n , K. & Wise, J. P., 1961. I n c i d e n c e of t h e cod p a r a s i t e Lernaeocera branchialis in t h e N e w
E n g l a n d a r e a , a n d its p o s s i b l e u s e as a n i n d i c a t o r of c o d p o p u l a t i o n s . - Limnol. O c e a n o g r . 6, 61-67.
StrQm, H., 1762. P h y s i s k o g O e c o n o m i s k B e s k r i v e l s e o v e r F o g d e r i e t S o n d m o r b e l i g g e n d e i. B e r g e n s Stift i N o r g e . Strom, Soroe, 1, 1-552.
S u n d n e s , G., 1970. Lernaeocera branchialis (L.) o n c o d (Gadus m o r h u a L.) in N o r w e g i a n w a t e r s .