THE FECUNDITY, TIME OF EGG DEVELOPMENT AND JUVENILE PRODUCTION IN SPINY-CHEEK CRAYFISH (ORCONECTES LIMOSUS) UNDER CONTROLLED CONDITIONS

We comprehensively describe the fecundity and time of embryonic development of the spiny-cheek crayfish (Orconectes limosus). Linear relationships between female size and ovarian fecundity, pleopodal fecundity, and production of juveniles at the 3rd stage, were confirmed. The ovarian fecundity was evaluated for the smallest as well as largest females in the sampled population (43-93 mm of body length); the number of oocytes (eggs) ranged widely, between 46 and 505. No significant difference was found between the ovarian and pleopodal fecundity observed just after egg laying. The value of the female gonadosomatic index just before laying was 4.2 ± 1.8% (0.8-7.7%). The mean diameter of eggs on female pleopods was 1.8 ± 0.2 mm (1.45-2.15 mm). A statistically significant difference was found between the numbers of eggs carried on individual pairs of pleopods. Mean time from laying to hatching was 46 ± 3.8 days (37-56 days), i.e. 647 ± 39.9 CTU (Celsius Temperature Units = degrees Celsius × days). Mean production of juveniles at the 3rd stage was found to be 135.7 ± 67.24 (15-243) juveniles. The early sexual maturation and also high number of juveniles at the 3rd stage per female gives this species a good predisposition for quick establishment in new localities

Survival rates associated with in vitro low-temperature storage of kutum (Rutilus kutum) eggs

To study the effects of post-stripping oocyte ageing at low temperatures on the viability of kutum (Rutilus kutum) oocytes, unfertilised eggs of five females were stored in ovarian fluid at temperatures of 4 and 7 degrees centigrade for 24 hours post stripping (HPS). The stored ova of five female kutum were separately fertilised at 0 (i.e., control eggs fertilised prior to storage), 4, 8, 12, 16, 20, and 24 HPS. The eyeing and hatching rates were recorded as indices of the egg quality. The results indicated that the maximum eyeing and hatching rates of the eggs (92% and 74%, respectively) were observed at 0 HPS, whereas the storage of the eggs at 4 °C for 24 HPS decreased the eyeing and hatching rates to 36% and 28%, respectively. The use of the higher storage temperature resulted in a more rapid decrease in the egg viability: eyeing and hatching rates of 9% and 2%, respectively, were obtained after storage at 7 °C for 24 HPS. The present study demonstrated that stripped kutum eggs that are stored in ovarian fluid at 4 and 7 degrees centigrade should be fertilised within 12 and 8 HPS, respectively, to obtain viability rates higher than 50%

COMPARISON OF TRAP AND BAITED STICK CATCH EFFICIENCY FOR NOBLE CRAYFISH (ASTACUS ASTACUS L.) IN THE COURSE OF THE GROWING SEASON

Noble crayfish (Astacus astacus) were caught using traps and baited sticks in Svğtlohorská reservoir in the Czech Republic, and the catch efficiency and size and sex composition in catches were compared during the growing season (May-September). One trapping period per month (1.5 hour from 6-7: 30 pm) was applied. Trap catches were significantly higher in September compared to the other months, and baited stick catches were significantly higher in May, June and September. Baited sticks were significantly more effective than traps in all months except in July. Males dominated in all catches, except in September trap catches. Females were totally absent in traps in June, July and August. Baited sticks caught females more successfully than traps, especially females with eggs. Traps did not catch any females with eggs. Males and females caught by baited sticks were of larger size range (range of body length 60-125 mm) than those caught by traps (range of body length 75-120 mm) however, there were no significant differences in mean size. Due to high catch efficiency, baited sticks may be considered as an appropriate catching gear in crayfish monitoring projects, especially when a short-time catching effort is required

Rearing conditions and life history influence the progress of gametogenesis and reproduction performances in pikeperch males and females

International audienc

COMPARISON OF TRAP AND BAITED STICK CATCH EFFICIENCY FOR NOBLE CRAYFISH (ASTACUS ASTACUS L.) IN THE COURSE OF THE GROWING SEASON

Noble crayfish (Astacus astacus) were caught using traps and baited sticks in Svğtlohorská reservoir in the Czech Republic, and the catch efficiency and size and sex composition in catches were compared during the growing season (May-September). One trapping period per month (1.5 hour from 6-7: 30 pm) was applied. Trap catches were significantly higher in September compared to the other months, and baited stick catches were significantly higher in May, June and September. Baited sticks were significantly more effective than traps in all months except in July. Males dominated in all catches, except in September trap catches. Females were totally absent in traps in June, July and August. Baited sticks caught females more successfully than traps, especially females with eggs. Traps did not catch any females with eggs. Males and females caught by baited sticks were of larger size range (range of body length 60-125 mm) than those caught by traps (range of body length 75-120 mm) however, there were no significant differences in mean size. Due to high catch efficiency, baited sticks may be considered as an appropriate catching gear in crayfish monitoring projects, especially when a short-time catching effort is required

MIGRATORY ABILITY OF ORCONECTES LIMOSUS THROUGH A FISHPASS AND NOTES ON ITS OCCURRENCE IN THE CZECH REPUBLIC

The occurrence of the spiny-cheek crayfish in the Czech Republic was first reported in the 1980´s in the Elbe River and is a result of its upstream migration from Germany. This study confirms that this species occurs in many other localities across the Czech Republic. Its migration ability was experimentally studied at a thirty-chambers fishpass located at a hydroelectric power station in the Elbe River. Group-marked crayfish were placed into 3 selected chambers. Their up- and downstream movement was then registered for 30 min after crayfish stocking. We found that a large portion of the experimental crayfish was passively carried along the stream and was caught in the lowest chamber. The movement of crayfish against the water current towards the higher-positioned chambers was not recorded. However, crayfish showed to have a high ability to hold their position in a strong water flow. Overall, 56.7 ± 9.43%, 6.7 ± 9.43% and 3.3 ± 4.71% of crayfish remained in the chamber of insertion and 23.3 ± 4.71%, 30.0 ± 14.14% and 26.7 ± 17.00% of crayfish migrated to the lower-positioned chambers