Straminipilous organisms growing on herbivorous pirapitinga ( Piaractus brachypomus ) and carnivorous piranha ( Pygocentrus nattereri ) from Poland

We investigated the growth of straminipilous organisms on the skin, muscles and liver of herbivorous pirapitinga (Piaractus brachypomus) and carnivorous piranha (Pygocentrus nattereri) in water of three different eutrophication levels. Sixteen straminipilous organism species were found growing on the investigated body parts of both species of fish used as baits. The higher number of species was found on the baits of carnivorous species (15) when compared with the ones from the herbivorous pirapitinga (10 species). The highest number of straminipilous organisms species developed on the skin of both species of fish. The highest number of species of straminipilous organisms was observed growing in the water of the Biała river (middle eutrophication), while the lowest number occurred in the baits of vessels with water from the Dojlidy pond (low eutrophication).


Introduction
In their natural environment, Piaractus brachypomus and Pygocentrus nettereri inhabit inland waters of South America (Thorson, 1976;Menni et al., 1996).In many countries, including Poland, both species are reared in amateur aquaria for their characteristic body colouration and original appearance.In aquarium conditions, they sometimes alter their behaviour, e.g.predatory piranha lose their aggressive disposition, become anxious and skittish, retaining, however, their atractive look due to their colourful skin.The aim of this study was to supply some data to extend the list of straminipilous organisms growing on chosen parts of the body of the pirapitinga and piranha specimens, used as baits.The result was to compare the composition, abundance and diversity in water from three trophically different water bodies in Poland.

Material and Methods
The analysis involved skin, muscles and liver dissected from a number of fish of two aquarium -reared pirapitinga and piranha.These were individuals of both sexes of herbivorous pirapitinga (Piaractus brachypomus Cuvier, 1818) and carnivorous, predatory red piranha (Pygocentrus nattereri Kner, 1858).The fishes were killed and 10 g samples of the body organs were immediately dissected and transferred to vessels.recommended instructions (Seymour and Fuller, 1987).The analyses of water and experiments were carried out in three parallel repetitions.
The pieces of baits from each vessel were observed every 3-4 days under a light-microscope and the presence of morphological structures (zoospores, antheridia and oogonia) of aquatic straminipilous organisms was recorded.The experiments were carried out for one month.
The straminipilous species were identified using the keys of Batko (1975), Pystina (1998) and the authors of the respective species.The systematics of straminipilous organisms was according to Dick (2001).

Results
Hydrochemical parameters of water used in the experiments are presented in Table 1.The most eutrophic was the water of the Fosa pond (most) and the Biała river (middle eutrophication) however, the water of the Dojlidy pond had the lowest content of ammonium nitrogen and phosphates.The highest levels of the BOD 5, COD, CO 2 , chlorides, magnesium and iron concentration were found in the Fosa pond.Water from Dojlidy pond contained the lowest levels of COD, CO 2 , sulphates, chlorides, magnesium and iron.
Sixteen straminipilous species were found growing on the investigated body parts of fishes (Table 2).The record of a few straminipilous species rare to the hydromycology of Poland and for fishes is worth special note, including Olpidiopsis saprolegniae, Saprolegnia litoralis, S. salmonis, Pythium diclinum (syn.Pythium gracile Schenk) and P. torulosum.The highest number of Water samples for the experiments were collected from three different water bodies: • River Biała, length 9.8 km, a left bank tributary of the Supraśl river flowing through Białystok City; • Dojlidy Pond, located near Białystok City, area 34.2 ha, maximum.depth 2.85 m, southern shores border with coniferous woods and western shores with Białystok City; • Fosa Pond, area 2.5 ha, maximum depth 1.75 m.
Pond with wild ducks and breeding swans as well as crucian carp, used by anglers.The pond is surrounded by meadows with linden and elm.Water samples for the analysis and the experiments were collected from each reservoir at a depth of 15-25 cm at a distance of 0.5 m from the bank.The water was filtered through a gauze and then poured to vessels.Nineteen parameters were determined for physical and chemical characteristics of the water using standard methods (Greenberg et al., 1995).
The following procedure was used while determining the presence of straminipilous organisms species on the investigated body organs of the fishes.Water samples (800 mL each) were placed in a 1,000 mL vessel.For each body part of each species from each water body, three vessels were collected.To every vessel were transferred 5-10 small pieces of suitable body part in accordance to the general principles of culture (Fuller and Jaworski 1987).All vessels were enclosed in Petri dishes with the bed turned upside down to prevent possible airborne contamination in the vessels with fungal spores.The vessels were stored at 15 ± 2 °C, with access to daylight resembling natural conditions and following the The highest number of species of straminipilous organisms was growing on both species of fishes in the water from river Biała, the lowest number in the water from Dojlidy pond.As is known, the water of Biała river is more eutrophic than the water of the Dojlidy pond.We observed similar phenomenon examining the straminipilous organisms growing on the eggs of acipenserid fishes (Czeczuga et al., 1995).
Only Saprolegnia parasitica was found on all of the investigated parts of the body of both species of fish.Saprolegnia parasitica causes mass death of eggs (Lartzeva, 1986;Hatai et al., 1990;Czeczuga et al., 2005), fish fry (Czeczuga and Muszyńska, 2000) and adult fish specimens (Frick and Reinhold, 1987;Hatai and Hoshiai, 1992).Olpidiopsis saprolegniae was first described by Braun (1856) as Chytridium saprolegniae, as a parasite of species of the genus Saprolegnia.Cornu (1872) transferred this species to the genus Olpidiopsis.In this study, Olpidiopsis saprolegniae was found growing only on the straminipilous species developed on the skin of both species of fish.The highest number of species of straminipilous organisms was observed on baits placed in the water from the Biała river, while the lowest number occurred in the water of the Dojlidy pond.Also the higher number of species was found on baits of the carnivorous species of piranha (15) when compared with the ones of the herbivorous pirapitinga (10).

Discussion
In this study the highest number of straminipilous species were growing on the cornivorous piranha.A similar phenomenon we observed examining aquatic straminipilous organisms growing on avian excrements.The higher number of straminipilous organism species was found on the excrement of carnivorous birds than in the herbivorous species of mud and waterbirds (Czeczuga and Mazalska, 2000).

Table 1 .
Chemical and physical properties of water in the three water bodies studied.

Table 2 .
Straminipilous organisms recorded on six body parts of piranha and pirapitinga obtained in three different water bodies.