Fróðskaparrit

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SEASONAL CHANGES IN THEINFECTION OF YOUNG SAITHE

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Fig. 2. a. The number offemales (white) and males (black) in samples of 1-year old saithe.

Talið av kvennfiski (grátt) og kallfiski( svart) hjá 1-ára gomlum seiði.

Fig. 2. b. The number offemales (white) and males (black) in samples of2-year old saithe.

Talið av kvennfiski (grátt) og kallfiski (svart) hjá 2-ára gomlum seiði.

cephalean Echinorhynchus gadi were re-

covered from the gut lumen (adults) or in

the pyloric caeca (larvae). The prevalence

and intensity of infection are shown in Figs.

4 and 6. A single record was made of the

crustacean laerneopodid ectoparasite Clav-

ella sp. and an unknown cestode plerocer-

coid. As the stomach is not included in this

study, no digeneans have been recorded.

Discussion

The results in this study showed a general

increase through one calendar year in the

prevalence of infection of young saithe

with A. simplex. The mean intensity of in-

fection was increasing for the 1-year old

saithe, but seemed stable for the 2- year old

saithe. Similar patterns, but at lower levels

were revealed for P. decipiens and Contra-

caecum sp. How can these fmdings be in-

terpreted?

A population of fishes which is infected

by a population of parasites may be so in

two principal ways. Either the infection is

continuous (an even or random distribution

is presumed for the infected intermediate

host(s)), or the infection is non-continuous

(a discrete or uneven distribution of the in-

fected intermediate host). In the first case

the prevalence of infection is expected to fit

a simple linear function, but in the latter

case a more complicated, non-linear func-

tion could be expected.

The prevalence of infection for Anisakis,

Pseudoterranova and Contracaecum in this

study appear to increase linearily with time

(Fig. 4a), so the process of infection for

saithe in this area most likely is continuous.