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Salton Sea Symposium 2000

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The following represents a modified version of a poster presented
at The Salton Sea Symposium, January 13-14, 2000,
Desert Hot Springs, California,
sponsored by the Salton Sea Authority
.  
 

Ectoparasites of Fish and Invertebrates of the Salton Sea

Boris I. Kuperman and Victoria E. Matey

Center for Inland Waters and Department of Biology

San Diego State University, San Diego, CA 92182

 

ABSTRACT

For many decades, the Salton Sea has been the site of an unprecedented series of die-offs of fish and water birds. These mortality events have been associated with critical combinations of high temperature and salinity, low oxygen tension, and toxic algal blooms. Recently, bacterial and viral pathogens have been documented or suspected as a cause of some of the massive birds and fish kills. Until 1997 nothing was known about parasites and their roles in fish disease at the Salton Sea.

Parasitological monitoring was carried out in 1997-1999. A total of 1,512 fish were examined from 6 locations along the shoreline of the Salton Sea (Fig. 1). The young of tilapia, croaker, and longjaw mudsucker were found infected by ectoparasites. Some permanent and persistent infestations of fish by such parasites were discovered around the perimeter of the Salton Sea at Varner Harbor, Bombay Beach, Red Hill Marina and Salton City. Invertebrates such as pile worms and copepods that represented the major food items for fish were also infected.

Three species of parasitic protozoans: the dinoflagellate Amyloodinium ocellatum, the ciliate Ambiphrya ameiuri; and the flagellate Cryptobia branchialis, and two species of parasitic flatworms, Gyrodactylus olsoni and Gyrodactylus imperialis were found on fish from the Salton Sea (Figs. 2-4, 7 & 8). Parasitic protozoans infected fish from spring through fall with extremely high intensity (Fig. 6). All these ectoparasites affect fish gills and skin, which are the major respiratory organs for young fish. Both parasitic protozoans and flatworms changed the general structure of fish gills and skin and caused alterations that may suppress respiratory functions and cause fish suffocation ( Figs. 2, 5 &, 8, d). The numerous sites of epithelial damage also represent portals of entry for bacterial, viral and fungal infections.

The pile worm, Neanthes succinea, was heavily infected by peritrich Epistylis sp., that were attached to their body segments and locomotory organs (Fig.9). Another peritrich, Rhabdostyla vernalis, was distributed over the body surface of the copepod Apocyclops dengizicus (Fig.10). Heavily infected invertebrates may decreased locomotor capabilities and become easy prey for predators.

Parasites appear to be an important stressor affecting fish populations in this unique water body. If they are a major cause of juvenile fish mortality, as seems likely, they may play a major role in determining fish population dynamics in the Salton Sea.

 

 

 

Fig. 1. Map of the Salton Sea. Sites of fish sampling.
 

 

[Click on genus and species name to reach larger images of that parasite]  

 

Fig 2. Amyloodinium ocellatum on the gills (a-c) and skin (d) of young tilapia. Pathological alterations of tissues, SEM.

Amyloodinium ocellatum

(Dinoflagellida)

a - swelling of gill filaments and fusion of respiratory lamellae.
b - erosion of gill epithelium of the site of parasite attachment.
c - lesion on the surface of gill epithelium after detachment of parasite.
d - degeneration of epithelial cells and concentration of bacteria at the site of parasite attachment

 

Fig. 3. Massive infestation of fry tilapia by Ambiphrya ameiuri, SEM.
Ambiphrya ameiuri (Peritricha)
a - head and eye.
b - body surface and pelvic fin.

 

 

Fig. 4. Distribution of Ambiphrya ameiuri on the (a) croaker gills and (b) tilapia skin, SEM
(a) croaker gills.
(b) tilapia skin, SEM.

 

 

Fig. 5. Alterations of tilapia skin after detachment of Ambiphrya ameiuri, SEM. Impressions (a) and scars (b) on the epithelial tissue.
a. Impressions.
b. on the epithelial tissue. 

 

 

Fig. 6 Seasonal variation in infestation of tilatpia in Varner Harbor, 1998-1999 by Amyloodinium ocellatum and Ambiphrya ameiuri. At top of figure are water temperatures measured at 20-30 cm depth at time of collection of fish (variable). Asterisks (*) denote the absence of parasites on fish examined.
 

 

Fig. 7. Heavy infestation of tilapia gills by Cryptobia branchialis, SEM. a - swelling of gill filaments and overproduction of mucus, b - parasite attachment to gill epithelium.
Cryptobia branchialis

(Bodonidae: Kinetoplastida)

a - swelling of gill filaments and overproduction of mucus.
b - parasite attachment to gill epithelium. 

 

 

Fig. 8. Gyrodactylus olsoni on the gill filament of longjaw mudsucker, SEM. a - general view, b - attachment organ, c - anchors and marginal hooks of the attachment organ, d - penetration of anchors into epithelial tissue.
Gyrodactylus olsoni

(Monogenea)

a - general view.
b - attachment organ.
 
c - anchors and marginal hooks of the attachment organ.
d - penetration of anchors into epithelial tissue

 

 

Fig. 9. Infestation of pile worm by Epistylis sp., SEM. a - anterior part, b - posterior part, c - cluster of peritrichs on body surface.
Epistylis sp. ( Peritricha) 

a - anterior part.
b - posterior part.

c - cluster of peritrichs on body surface.
Fig. 10. Infestation of Apocyclops dengizicus by Rhabdostyla vernalis, SEM. a - distribution on the copepod body, b - general view of organisms.
Rhabdostyla vernalis (Peritricha)
 
a - distribution on the copepod body.
b - general view of organisms.

 

 

Original Abstract

Parasites of fish and invertebrates are integral parts of aquatic ecosystems. Especially in water bodies with poor environmental conditions they can exert a strong regulatory effect on populations. Environmental stresses can depress host immunity. Fish become more susceptible to infections and these can become more severe, even fatal. Sick and dead fish can become a source of disease for piscivorous birds and can present serious threats to their health.

For many decades, the Salton Sea has been the site of an unprecedented series of die-offs of fish and water birds. These mortality events have been associated with critical combinations of high temperature and salinity, low oxygen tension, and toxic algal blooms. Recently, bacterial and viral pathogens have been documented or suspected as a cause of some of the massive birds and fish kills. Until 1997 nothing was known about parasites and their roles in fish disease at the Salton Sea.

Parasitological monitoring was carried out in 1997-1999. A total of 1,512 fish were examined from 6 locations along the shoreline of the Salton Sea. The young of tilapia, croaker, and longjaw mudsucker were found infected by ectoparasites that is parasites that attach to the external body surfaces. Some permanent and persistent infestations of fish by such parasites were discovered around the perimeter of the Salton Sea at Varner Harbor, Bombay Beach, Red Hill Marina and Salton City. Invertebrates such as pile worms and copepods that represented the major food items for fish were also infected.

We found that fish from the Salton Sea are infected by three species of parasitic protozoans: the dinoflagellate Amyloodinium ocellatum, the ciliate Ambiphrya ameiuri; and the flagellate Cryptobia branchialis, and two species of parasitic flatworms, Gyrodactylus olsoni and Gyrodactylus imperialis. The protozoans range from 7.5 µm to 129 µm in length, the flatworm from 261µm to 312 µm. These parasites are dangerous and sometimes spread pathogens for fish in aquaculture facilities. In nature, however, infestations by these parasites are usually low. At the Salton Sea, parasitic protozoans infected fish from spring through fall with extremely high intensity. In summer months of 1997-1999, 100% of fish from 6 locations examined were infected by the dinoflagellate A. ocellatum. Hundreds of these dangerous and destructive parasites were attached to fish gills. In spring and autumn during 1997-1999, about 100% of fish fry from the same locations along the shoreline were heavily infected by the ciliate A. ameiuri, which completely covered fish skin, fins and, rarely, gills. In autumn 1997, an outbreak of fish infestation by C. branchialis was found at Bombay Beach. Parasites tightly covered the gill surface. Parasitic flatworms G. olsoni and G. imperialis infected gills longjaw mudsucker and tilapia in different seasons. Their numerous hooks penetrated deeply into epithelial tissue of gills, skin and fins, heavily damaging it.

All these ectoparasites affect fish gills and skin, which are the major respiratory organs for young fish. Both parasitic protozoans and flatworms changed the general structure of fish gills and skin and caused numerous lesions, local erosion, and severe irritation at sites of their attachment to epithelial tissues. These alterations of fish gills and skin may suppress respiratory functions and cause fish suffocation. The numerous sites of epithelial damage also represent portals of entry for bacterial, viral and fungal infections.

The pile worm, Neanthes succinea, was heavily infected by peritrich Epistylis sp., individuals of which were attached to their body segments and locomotory organs. Another peritrich, Rhabdostyla vernalis, was distributed over the body surface of the copepod Apocyclops dengizicus. It is suggested that heavily infected invertebrates have decreased locomotor capabilities and become easy prey for predators.

Parasites appear to be an important stressor affecting fish populations in this unique water body. If they are a major cause of juvenile fish mortality, as seems likely, they may play a major role in determining fish population dynamics in the Salton Sea.



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