Andreja Lucić

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha in the Drava River

The effects of the trematode Bucephalus polymorphus on the reproductive cycle of the zebra mussel Dreissena polymorpha were examined in mussel populations from the Drava River. The reproductive cycle was studied by histological examination of the gonads and quantified by an image analysing system to determine changes in volume of the entire visceral mass, gonads, digestive glands and in particular the volume of trematodes. Results confirmed that (1) gonads of D. polymorpha were affected by B. polymorphus infection more than any other organ and (2) development of cercariae in sporocysts of B. polymorphus coincides with host gonad maturation. This is the first study in which the image analysing system was used to determine the effect of trematodes on the reproductive cycle of D. polymorpha. Also, this is the first record of sporocysts of B. polymorphus in D. polymorpha in this part of Europe.

Aquatic Macroinvertebrates of the Sava River

The objective of this chapter is to present the data on aquatic macroinvertebrate communities along the Sava River, based on investigation performed during 2011 and 2012 at 12 sampling sites within the sector between Vrhovo (Slovenia) and Belgrade (confluence to the Danube). During our study 227 macroinvertebrate taxa were recorded in the Sava River. Having in mind that upper stretch of the Sava River was not covered by this work (alpine and subalpine stretch), as well as based on the review of previous works on the macroinvertebrate fauna of the Sava River, more than 300 species will be confirmed for the Sava River. The data on the distribution of aquatic macroinvertebrates revealed five different stretches—alpine, subalpine, Upper Sava plain, Middle Sava and Lower Sava. Physical habitat degradation, pollution and pressure caused by biological invasions were found to be the main factors of endangerment of aquatic macroinvertebrate fauna diversity. There is an obvious need for further investigation of the Sava River in order to complete the data on aquatic macroinvertebrates and to provide the basis for accurate assessment of environmental status of the river.

Seasonal changes of the condition indices and haemocyte counts of the Austropotamobius torrentium population in Kraljevec Stream, Croatia

The stone crayfish, Austropotamobius torrentium (Schrank, 1803) is one of the four native European crayfish living in Croatian freshwaters. Kraljevec Stream is situated on the southern slopes of Medvednica Mountain (north-west Croatia) at 400 m above sea level. Our research was carried out for one year, from May 2003 to April 2004. During the study period water temperature varied between 2 to 17.2°C, alkalinity between 100 and 200 mg CaCO 3 /L, the mean oxygen concentration and pH was 12.1 mg/L and 8.3, respectively. Crayfish were trapped by baited hand made traps, which were secured in a stream current with the stones and roots of the surrounding trees. We caught 100 crayfishes, 68 males and 32 females. Hemolymph was sampled 10 to 15 min after the catch. EDTA anticoagulant was used to prevent hemolymph coagulation and 10% formalin was used to fix haemocyte for differential counts. Each month five or six specimens of each sex, if possible, were sacrificed and hepatosomatic, gonadosomatic and muscle indices were measured. We found statistically significant differences in hepatosomatic and gonadosomatic indices between months and between sexes. Muscle indices were significantly different between males and females. The average total haemocyte counts were 7.6 · 10 5 cells/ ml and 6.5 · 10 5 cells/ml hemolymph for males and females, respectively. The average hyalinocyte, granulocyte and semigranulocyte ratio was 77: 14.5: 8.5%. There were no statistically significant differences in total haemocyte counts between months and between sexes.

A comparative study of the physiological condition of native and invasive crayfish in Croatian rivers.

The physiological condition of two invasive crayfish species identified in Croatian rivers (Orconectes limosus and Pacifastacus leniusculus) was compared with that of native crayfish populations (Astacus astacus and A. leptodactylus). Hepatosomatic, gonadosomatic and abdominal muscle indices were examined for all four species and within a specific invadernative pair. The results demonstrate that invasive crayfish had better overall physiological condition when compared to native species, with a higher energy content of the hepatopancreas, abdominal muscle and gonads in invasive than in native species, with the exception of A. leptodactylus females which demonstrated an increased ability to allocate energy to reproduction in comparison with other species. These results also indicate that A. astacus is physiologically more unstable than A. leptodactylus and thus more likely to be outcompeted and replaced by non-indigenous crayfish species.

Seasonal distribution of the zebra mussel larvae in the dam reservoirs Dubrava, Čakovec, and Varaždin, Croatia

Rad se bavi problematikom vertikalne i horizontalne stratifikacije licinki skoljkasa Dreissena polymorpha u akumulacijskim jezerima hidroelektrana Dubrava, Cakovec i Varaždin. Prikazana je distribucija i gustoca licinki D. polymorpha ovisno o koncentraciji klorofila i temperaturi vode.