Maladies des organismes aquatiques (document en anglais)

DISEASES OF AQUATIC ORGANISMS

Dis Aquat Org

Vol. 65: 177–180, 2005

Published June 30

NOTE

Hyperparasitism of trichodinid ciliates on monogenean gill flukes of two marine fish

A. Colorni*, A. Diamant

Israel Oceanographic and Limnological Research, National Center for Mariculture, PO Box 1212, Eilat 88112, Israel

ABSTRACT: Two unusual cases of hyperparasitism of trichodinid ciliates on monogenean gill flukes

are described from southern Israel (Red Sea). The first case occurred in cultured European sea bass

Dicentrarchus labrax infected by Diplectanum aequans, while the second was observed in a feral

devil firefish Pterois miles infected by Haliotrema sp. In both cases, the trichodinids heavily coinfested

the host fish gills. The flukes were

completely coated by the ciliates, which gave them a

cobblestone

appearance, but no damage to their tegument was apparent.

Both cases are

most likely

a

result

of accidental hyperparasitism, brought

about by perturbed

environmental

conditions.

KEY WORDS: Diplectanum · Haliotrema · Hyperparasitism · Marine fish · Monogenea · Trichodina

Resale or republication not permitted without written consent of the publisher

Trichodinid protozoans and monogenean flatworms

are cosmopolitan aquatic parasites, common on gills

and skin of fish in both the freshwater and marine

environments. Trichodinids are peritrich ciliates (order

Mobilina, family Trichodinidae) that glide on the

surface of the fish. They normally feed on bacteria and

mucus and are often considered as ectocommensal

nuisances rather than true parasites. However, weakening

of the host’s

resistance

may encourage their

proliferation.

Their repeated

adherence

and suction

cause

epithelial hyperplasia and hypertrophy

in the

host.

On debilitated individuals, trichodinids are

more

aggressive,

and cell debris and erythrocytes

are

often

found

in their food vacuoles (Lom 1995, Noga 1996).

Transmission

is direct,

from

fish to fish. Within

8 to 10 h

of

the host’s

death, trichodinids leave the host but,

depending

on the temperature,

may survive

for several

days

in the water (Davis 1961).

Monogeneans are ectoparasitic platyhelminths that

feed on the superficial layers of fish skin and gills.

Most species of Monogenea have a narrow host range

and are restricted to a single species, genus, or family

(Rhode 1982, Noga 1996). Proliferation of both tricho-

dinids and monogeneans is generally an indication of

poor water quality, a stressed, debilitated fish host, or

both (Noga 1996). Concurrent infections of trichodinid

ciliates and monogenean flukes (e.g. Gyrodactylus,

Microcotyle, Lamellodiscus) are not uncommon in

cultured fish, where they may act with synergistic

deleterious effects (Noble 1963, McVicar & MacKenzie

1977, Cruz E Silva et al. 1997).

The present report describes 2 unusual cases of

hyperparasitism of trichodinid ciliates on monogenean

flukes. The first case was observed in March 2001 in a

100 m

3

concrete pond holding approximately 30 000

European sea bass Dicentrarchus labrax of about

200 g, whose gills were found to be heavily infected by

a trichodinid and moderately infected by Diplectanum

aequans. Water temperature in the pond was 22 ± 1°C

and salinity 40‰. The fish had a history of light,

chronic Mycobacterium marinum infections and were

also infected with Streptococcus iniae, a gram-positive

bacterium that produced septicemia with lethal consequences

for some 40%

of the stock. The streptococcosis

...