Search

The reproductive cycle of Astacus astacus was described by the external observation of the gonads, recording changes in the gonadosomatic index (GSI) and by the histological analysis of the reproductive organs. A total of 37 males and 13 females of Astacus astacus were collected from the Vukovina gravel pit located at northwest Croatia from May 2003 until January 2004. All crayfish were mature with total body lengths between 7.84 and 13.7 cm and weights between 16 and 125 g. There was a pronounced difference between the GSI values of the sexes. GSI fluctuated within a very small range (between 0.2 and 1.5%) in males while in females it increased up to 12.3% during the mating season. The external appearance of the testes and ovaries during the reproductive cycle was compared with the histological sections of germ cells in the testes, the vas deferens and ovaries. Besides the germinative cells, the morphological changes in testis and vasa deferentia of A. astacus extended also to the connective tissue and secretory epithelium. The maturation of germinative cells was synchronized, both in testes and ovaries.

The aim of our research was to gather information about the reproduction cycle of Austopotamobius torrentium in Croatia. The research was conducted between October 1998 and April 2000 in streams on the Medvednica Mountain (north-west Croatia). We caught 767 females, of which 92 (11.99%) were berried. Berried females were captured from the beginning of November until mid June of the following year. Total length (from the tip of the rostrum to the end of telson) of the smallest female with pleopodal eggs was 5.40 cm, while the longest was 8.70 cm. Diameter of pleopodal eggs varied from 0.24 cm to 0.34 cm (mean ± SD = 0.28 ± 0.02) and their number per female from 1 to 104. Correlations between female size (total length and weight), number of pleopodal eggs and egg diameter were done. We found positive correlation between female length and number of eggs (r = 0.46) and between female length and egg diameter (r = 0.29), as well as between female weight and egg number (r = 0.50) and female weight and egg diameter (r = 0.30). Weak positive correlation was recorded between number of eggs and their diameter (r = 0.06).

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 CaCO3/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 × 105 cells/ ml and 6.5 × 105 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.

Psorospermium haeckeli is a thick-walled unicellular organism widely reported in European astacid crayfish. It is typically referred to as a “parasite” although its pathogenic impact remains unclear. Until now there were no data about its presence in Croatian astacid crayfish. We examined 144 specimens of the three astacid species from 12 different locations and found sporocysts of Psorospermium in 13 preparations of epidermal connective tissue of Astacus astacus and Astacus leptodactylus. Preparations were made by scraping the epidermal-connective tissue from under the carapace, treating it with 10% KOH and viewing it under a microscope at 125×, 250× and 400× magnification. A relative scale was used to describe the degree of infection of the crayfish by Psorospermium. We found two types of mature sporocysts and also some developing stages of Psorospermium. In the A. leptodactylus we found many sporocysts that were fully melanised. Further investigations are needed to understand the distribution of infected crayfish in Croatia and patterns of their infection with Psorospermium.

Astacus astacus is one of four native European crayfish species living in Croatian freshwaters. It is naturally distributed in rivers belonging to the Black Sea Basin. To some rivers of the Adriatic Sea Basin, however, it had been introduced by man. According to the information from local people it is most likely that A. astacus has been introduced into the Velika Paklenica Stream during the first half of the 20th century. Our study stream, draining the Velebit Mountain, is situated in Paklenica National Park, Middle Adriatic. The fieldwork of our study was performed during July 2000 and 2002, respectively. To estimate the population size we used mark-recapture techniques (Jolly-Seber Method, Schnabel Method and Schumacher and Eschmeyer Method). Crayfish were trapped with baited LiNi traps that were set along the stream banks at 10 m intervals and left there overnight. Caught animals were individually marked by piercing holes into the uropods and telson and then released. In July 2000 we caught 233 crayfish in total, from which 70 specimens were trapped more than once. In July 2002 we caught 296 crayfish, from which 86 were trapped more than once. Differences in the population size between the two years are discussed.

In order to gain better insight into the distribution of white-clawed crayfish (Austropotamobius pallipes) in Croatia, we pooled together all of the available historical and recent data. The historical data on distribution were compiled from literature and the Croatian Natural History Museum collection. Fieldwork, to evaluate the current distribution of crayfish, took place between 1995 and 2003. The distribution of Austropotamobius pallipes is restricted to the limestone region and therefore the species is found spread in rivers belonging to the Adriatic Sea basin (from NW to SE of Croatia). Those waters are mainly unpolluted and the substrate consists of rocks and stones and crayfish were found near banks. We also occasionally found crayfish in subterranean habitats but as they appear to have no troglomorphic adaptations they are probably of epigean origin. According to data taken from literature, both A. pallipes and A. torrentium live in the coastal rivers. But to date, we have not yet recorded presence of A. torrentium there, while we did record the presence of Astacus astacus. While studying the data from the literature, we were frequently confronted with contradictory findings, therefore, in the near future we are planning to do intensive field research within the coastal region in order to get a clearer picture of the detailed distribution of freshwater crayfish in this part of Croatia. In addition, individuals from four different geographical areas were compared using two morphometric and two meristic characteristics and the results are discussed.

We studied life cycle of stone crayfish for 18 months in three streams on Medvednica Mountain, located above city of Zagreb. Sampling of animals was carried out with baited traps twice a month and various physiological functions were recorded. Sex ratio of trapped crayfish was 1:1, but it fluctuated during the year. Animals were active from early spring until the beginning of November when their activities significantly decreased. In this period we noticed three peaks of higher activity. The first one after winter starvation in March, the second one after egg hatching (June/July) and the third one during mating period (end of September - beginning of November). The maximal recorded weight for female was 38 g while the heaviest male was 55 g. The longest female was 9.28 cm and male 10.30 cm. Development of glair glands started from the end of July, mating occurred at the end of October and the juveniles hatched until mid-June. Freshly moulted animals were found from mid-May until mid-October. Main injuries were claw and limb loss. We noticed the presence of burn spot disease and Branchiobdella parasita Henle within studied populations. Correlation with five different physico-chemical parameters of water showed that animals’ activity is positively correlated to water temperature, conductivity, pH and hardness and negatively to oxygen concentration.