ZOOSPORIC FUNGI GROWING ON THE SPECIMENS OF CERTAIN FISH SPECIES RECENTLY INTRODUCED TO POLISH WATERS

Mycoflora developing on some fish species, recently introduced to Polish waters, has not been known. The authors incubated muscles of four fish species (monkey goby, Neogobius fluviatilis; racer goby, N. gymnotrachelus; Chinese sleeper, Perccottus glenii; and stone moroko, Pseudorasbora parva caught in the drainage area of the Bug River) in water taken from 6 different places. A total of 59 fungus species were found to grow on fish muscles studied: Achlya ambisexualis, A. americana, A. caroliniana, A. crenulata, A. debaryana, A. diffusa, A. dubia, A. intricata, A. klebsiana, A. oblongata, A. oligacantha, A. orion, A. polyandra, A. prolifera, A. proliferoides, A. radioasa, A. rodrigueziana, A. treleaseana, Aphanomyces irregularis, A. stellatus, Blastocladiella britannica, Blastocladiopsis parva, Catenaria verrucasa, Cladolegnia unispora, Dictyuchus monosporus, Isoachlya monilifera, Leptolegnia caudata, Leptomitus lacteus, Phlyctochytrium aureliae, Pythium afertile, P. aquatile, P. arrhenomanes, P. butleri, P. dissotocum, P. hemmianum, P. intermedium, P. myriotylum, P. ostracodes, P. periplocum, P. tenue, Rheosporangium aphamidermatus, Rhizophlyctis hirsutus, Rhizophydium laterale, R. macrosporum, Saprolegnia asterophora, S. diclina, S. eccentrica, S. ferax, S. hypogyna, S. litoralis, S. mixta, S. monoica, S. parasitica, S. pseudocrustosa, S. shikotsuensis, S. torulosa, S. uliginosa, Thraustotheca clavata, Zoophagus insidians. The results obtained may be important to ichthyopathologists, because 25 of the above-mentioned fungi are known as necrotroph or parasites of fishes.


INTRODUCTION
In the last decade of the 20 th century, the Polish ichthyofauna gained four new species which migrated to Poland from the south-east (Danilkiewicz 1997), namely monkey goby, Neogobius fluviatilis (cf. Danilkiewicz 1997), racer goby, Neogobius gymnotrachelus (cf. Danilkiewicz 1996), Chinese sleeper, Perccottus glenii (cf. Antychowicz 1994, Danilkiewicz 2000, and stone moroko, Pseudorasbora parva (cf. Witkowski 1991). One of the places they all have settled, is the middle stretch of the Bug River with some of its tributaries.
We have been focused, for some time new, on aquatic fungi, paying special attention to their contribution to the ecosystems of the respective bodies of water. Our studies have already covered all Polish freshwater fish species (Czeczuga et al. 1996, Czeczuga and Muszyƒska 1997a, 1998, 1999a. This time, to have a complete picture of fungi growing on fish, found in our country, we decided to examine the species introduced recently to Polish waters.

MATERIAL AND METHODS
This study was based on the muscles of the following fish species: the monkey goby, Neogobius fluviatilis (Pallas, 1814); racer goby, Neogobius gymnotrachelus (Kessler, 1857); Chinese sleeper, Perccottus glenii Dybowski, 1877; and the stone moroko, Pseudorasbora parva (Temnick et Schlegel, 1846) which were caught in October 2000 from the Bug River near Janów Podlaski. Specimens of Pseudorasbora parva were also obtained from the CieleÊnica River in the same area.
The water for the experiments was collected from six different bodies of water: springs Cypisek and Jaroszówka, ponds Fosa and Akcent, SupraÊl River, and Komosa Lake. Nineteen parameters of these water samples were determined (Table 1) according to the generally accepted methods (Greenberg et al. 1992).
The following procedure was followed while determining the presence of aquatic fungus species on the fish muscles. The muscles from 5 specimens of each species (10-20 fragments) were transferred to thirty 1.0-l vessels (5 in each) and placed in the laboratory at the temperature approaching that of respective body of water. The subsamples from each vessel were observed under a microscope and the presence of mycelium (forming zoospores and oogonia) of aquatic fungi growing on muscles was recorded. The methods were described in detail by Seymour and Fuller (1987). The samples of muscles were examined through one (or one and a half) week. The experiments were carried out for three weeks.

RESULTS
Hydrochemical analyses of water samples used for the experiment showed that the water from both ponds was the most abundant in nutrients, i.e. total nitrogen and phosphates, while the spring water contained fewer nutrients. This tendency was also visible in other hydrochemical parameters of these bodies of water (Table 1).
Fifty-nine zoosporic fungi species were found to grow on the muscles of four fish species introduced to the Polish waters (Table 2, Fig. 1). The fewest fungi developed on the muscles of Pseudorasbora parva (18), the most on Perccottus glenii (34 species). Such species as Rhizophydium macrosporum, Saprolegnia ferax, Saprolegnia parasitica, and Saprolegnia torulosa were observed on the muscles of all the four fish species examined. Of 59 fungus species, 25 are known as fish parasites or necrotrophs.
The most fungi were found on the fish muscles incubated in the water from two springs (Cypisek, 24; Jaroszówka, 27), the fewest-in the water from ponds (Fosa, 7; Akcent, 11 species). In the water from SupraÊl River, 17 fungus species were found on the fish muscles, while in that from Komosa Lake-18 (Table 3).   * species known as parasites or necrotrophs of fishes Table 3 Aquatic fungi found on the fishes studied, in water from different places DISCUSSION As revealed by the present study, species composition of aquatic zoosporic fungi growing on the muscles of the four species introduced to the Polish waters does not differ from the species composition encountered on native species (Czeczuga and Muszyƒska 1999a, b).
In mycological monographs, Leptomitus lacteus has been known as a sewage fungus (Batko 1975, McLaughlin et al. 2001) and a typical mycoflora representative of waters strongly polluted with municipal wastes. However, Lemon (1954) found this fungus to be a parasite of sea lamprey, while Willoughby (1970) encountered it on the specimens of young perch in Windermere. Our investigations observed its growth on coregonid eggs incubated in hatcheries (Czeczuga and Woronowicz 1993).
Saprolegnia hypogyna is known as a soil and aquatic saprophyte, and a facultative parasite on fish eggs. We found this fungus on the eggs of many fish species, including salmonids Muszyƒska 1996, Czeczuga et al. 1996).
Like in the case of other fish species (Czeczuga et al. 1995, Czeczuga and Muszyƒska 1997b, Czeczuga and Kiziewicz 1999, also in the four species examined, the most aquatic zoosporic fungus species were found to grow on fish living in less eutrophic waters (springs Jaroszówka and Cypisek), the fewest in polytrophic-type waters (ponds Fosa and Akcent). This could be associated with the phenomenon, known in hydrobiology, that in oligotrophic type waters the species number of hydrobionts is higher, being decreased in more eutrophic types; in polytrophic waters only one or two and seldom a few hydrobionts grow intensely. As shown in our previous and present study this also refers to aquatic zoosporic fungi.