Short Communication Prymnesium parvum, an Ichthyotoxic Alga in ...

The Israeli Journal of Aquaculture – Bamidgeh 60(1), 2008, 5-8. 5 

Short Communication 

Prymnesium parvum, an Ichthyotoxic Alga in an 

Ornamental Fish Farm in Southern Israel 

Nurit Gordon and Angelo Colorni* 

Israel Oceanographic and Limnological Research, National Center for Mariculture, 

P.O. Box 1212, Eilat 88000, Israel 

(11.9.07, Accepted 12.10.07) 

Key words: dinoflagellate bloom, Prymnesium parvum, molly, koi, ammonium sulfate 

Abstract 

The haptophyte alga Prymnesium parvum (Prymnesiophyceae) caused “creeping” mortality in 

ornamental fish, molly (Poecilia sp.) and koi (Japanese carp, Cyprinus carpio), farmed in the 

Arava Valley in southern Israel. The toxicosis occurred when the water system was changed 

from flow-through to closed circulation. A moderately high temperature, three-fold increase of 

salinity, and probable rise in eutrophication created conditions suitable to P. parvum blooms. The 

system was treated with 10 ppm ammonium sulfate and fish mortality ceased. 

Prymnesium parvum is a relatively small haptophyte 

phytoflagellate that produces toxins of 

lethal effect on gill-breathing animals and 

extensive fish mortality in brackishwater fishponds. 

It was first associated with ichthyotoxicity 

in the Netherlands (Liebert and Deerns, 

1924) and some years later in Denmark 

(Otterstrom and Steemann-Nielsen, 1939). In 

Israel, the flagellate was first described in carp 

ponds in the Beit She’an (Beisan) Valley in the 

northern part of the country in the fall of 1945 

(Reich and Aschner, 1947). Fish mortality was 

always preceded by a typical change of water 

color from transparent light green in healthy 

ponds to a dirty yellow-brown. The condition 

gradually spread south and in the following 

winter reached the ponds of Beit Ha’arava, a 

settlement north of the Dead Sea. Although 

situated some 100 km apart, the two locations 

shared the same water supply. Soon after this 

first case report, the toxicosis became enzootic, 

affecting an estimated 3,000 acres, 60% of 

the total Israeli pond area (Sarig, 1971). 

The toxicity of P. parvum was extensively 

studied in Israel (Yariv and Hestrin, 1961; 

Bergmann et al., 1963; Parnas, 1963; Reich 

et al., 1965; Dafni and Shilo, 1966; Shilo, 

1967). The alga produces prymnesin, a com- 

* Corresponding author. Tel.: +972-8-6361427, fax: +972-8-6375761, e-mail: 

angelo@ocean.org.il, colorni@attglobal.net

6 

Gordon and Colorni 

plex of highly toxic compounds whose synthesis 

is greatest during the late stages of logarithmic 

growth and stationary phases (Shilo, 

1967). The primary site of action of prymnesin 

appears to be the gill membrane, whose permeability 

becomes severely compromised 

(Yariv and Hestrin, 1961; Ulitzur and Shilo, 

1966). Fish may die within hours without presenting 

any particular anatomo-pathological 

lesions. Prymnesium parvum toxins can kill 

other aquatic organisms as well, including 

protozoans, cnidarians, turbellarians, rotifers, 

oligochaetes, polychaetes, irudineans, cladocerans, 

amphipods, isopods, gastropods, and 

amphibians in the gill-breathing stage 

(Valkanov, 1964; Paster, 1973). 

Although euryhaline and able to survive in 

fresh water (250 mg chloride per l water; 

Kimor, 1948), P. parvum requires a salinity of 

0.1-3% to grow (Shilo and Shilo, 1962; Larsen 

and Bryant, 1998). The optimum salinity for 

growth as well as the environmental factors 

that influence toxin production are uncertain 

(Larsen and Bryant, 1998), however, stagnating 

brackish water, raised nutrient concentrations, 

and a mild climate provide an ideal ecological 

niche for P. parvum and favor blooms 

(Collins, 1978; Holdway et al., 1978; Baker et 

al., 2007). 

In the past, confirmation of P. parvum was 

made by challenging small fish that are particularly 

sensitive to the toxin (such as Gambusia 

affinis) with an activator (3,3 diaminodipropylamine/DADPA) 

that lowers the minimal toxic 

concentration. Presence of at least 1 ITU 

(ichthyo-toxic unit) was confirmed by the death 

of all test fish within two hours (Ulitzur and 

Shilo, 1966). Prymnesium parvum blooms 

were controlled mainly by using 10 ppm 

ammonium sulfate (Reich and Aschner, 1947), 

10-15 ppm liquid ammonia (Sarig et al., 1960), 

or 2-3 ppm copper sulfate (Sarig, 1971). 

The present report describes a case 

brought to our attention in January 2007. 

Continuous, “creeping” mortality in an ornamental 

fish farm in the desert area of the 

Arava Valley started in 2003 when the water 

system, fed by local aquifers, was changed 

from flow-through to closed circulation. The 

fish were raised in a variety of ponds (concrete, 

plastic-lined, and earthen). The farm 

water temperature was maintained at 

25±1.5°C and salinity at the water inlet fluctuated 

within a range of 300-500 mg chloride 

per l water. After the change, effluent water 

flowed through a sedimentation pond and 

recirculated back to the fishponds. Fresh 

water was added to compensate for evaporation. 

Chloride in the ponds rose to 700-1100 

mg/l (1.3-2‰) during the algal toxication. 

Neither gross pathology nor parasitological 

or histopathological analysis of a sample 

of about 20 molly and koi revealed the presence 

of pathogens or any particular abnormalities, 

as in similar cases (Reich and 

Aschner, 1947; Sarig, 1971). Microscopic 

examination of the water, however, revealed a 

relative abundance (over 1 x 105 cells/ml) of 

P. parvum (length 13.5±1.5 µm, width 9±1 

µm; Fig. 1). A bloom of the green microalga 

Kirchneriella lunaris was also observed, as 

was the presence of the diatoms Chaetoceros 

and Skeletonema and the microflagellates 

Cryptomonas and Chlamydomonas. 

No mortality occurred in ten fish that were 

transferred to an aquarium containing fresh 

uncontaminated water and kept under observation 

for over a month, indicating that the fish 

were in an initial and still reversible stage of 

intoxication, a feature already noted by other 

authors (Ulitzur and Shilo, 1966). The system 

was treated with 10 ppm ammonium sulfate 

according to the recommendations of Reich 

and Aschner (1947) and the fish mortality 

stopped. 

The propagation of the P. parvum was 

quite clearly triggered by the up to three-fold 

increase in salinity and favored by the moderately 

warm water of the fishpond, probably 

together with the rise in eutrophication caused 

by recirculating the water. The renewed 

occurrence of P. parvum in this region is worrisome 

and may require new management 

strategies to control its spread. 

Acknowledgements 

This work was carried out in the Pathobiology 

Department, whose activities are generously 

supported by Dan and Florence Green, North 

American Friends of IOLR.

Prymnesium parvum in an ornamental fish farm in Israel 

7 

Fig. 1. Prymnesium parvum Carter from the Arava Valley in southern Israel. 

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