Potential fecundity of an introduced population, Keban Dam Lake, Elazı , Turkey, of freshwater crayfish, Astacus leptodactylus leptodactylus (Esch., 1852)

Potential fecundity of an introduced population, Keban Dam Lake, Elazı , Turkey, of freshwater crayfish, Astacus leptodactylus leptodactylus (Esch., 1852), was investigated in the present study. The results showed that there was not a linear relationship between female size and pleopodal egg number. The results also showed that although there is an increase in the mean pleopodal egg number with an increase in size (carapace length, CL), it is not the most important factor affecting potential fecundity in A. leptodactylus (slope=1.9294). Mean pleopodal egg number was 305.93 (S.E.=8.82) for the size range of 47–76 mm CL (N=96). The maximum pleopodal egg number was 588 for the crayfish in a 72-mm CL. The present study showed that Keban Dam Lake population of A. leptodactylus has more potential fecundity than the other populations in Turkey. The egg-bearing capacity of female A. leptodactylus caught from Keban Dam Lake could improve efficiency in controlled hatchery production of juveniles.     

The harvest of the freshwater crayfish <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz in Turkey: harvest history,impact of crayfish plague,and present distribution of harvested populations

This review focuses on the present distribution of populations of the crayfish Astacus leptodactylus that are harvested in Turkey. It also examines the history of this harvest and the impact that crayfish plague has had on them. Crayfish plague, caused by the fungus-like organism, Aphanomyces astaci Schikora, 1906, is a severe parasite of freshwater crayfish and has caused a lot of damage to A. leptodactylus populations in Turkey since 1984. Turkey was the largest provider of A. leptodactylus to Western Europe from 1970 (or possibly earlier) until 1986. For example, the peak production was reached in the early 1980s, with over 5,000 tonnes being exported in 1984. On the other hand, as a result of the crayfish plague the harvest of A. leptodactylus was reduced severely in most populations in Turkey after 1985. The harvest was only 320 tonnes in 1991. After the occurrence of crayfish plague in Turkey, in order to increase crayfish production uncontrolled A. leptodactylus stockings have been carried out in many waterbodies throughout Turkey. These introductions have caused an increase in the number of A. leptodactylus populations, but exploitation of A. leptodactylus is still under the pressure of the plague, although there has been a steady increase in crayfish production in recent years. The harvest increased to 2,317 tonnes in 2004. Fortunately, among those populations affected by crayfish plague, large amounts of A. leptodactylus can still be harvested from three lakes, ?znik (Bursa), E?irdir (Isparta) and Çivril (Denizli). Thus, it seems that A. leptodactylus has a degree of resistance to crayfish plague. It is therefore interesting to investigate the resistance of A. leptodactylus caught from these populations to crayfish plague.     

The effects of dietary nucleotide content on the growth performance,digestibility and immune responses of juvenile narrow clawed crayfish,Astacus leptodactylus leptodactylus Eschscholtz, 1823

A 126‐day experiment was carried out under controlled conditions to compare the effects of five levels (0.5, 1.0, 1.5, 2.0 and 2.5 g kg^?1) of dietary nucleotide (Vannagen^®) on the growth performance and biological indices of juvenile crayfish (8.25 ± 0.39 g). The protein efficiency ratio (PER, 1.69–2.17), lipid efficiency ratio (LER, 2.29–3.00), energy efficiency ratio (EER, 2.68–3.65), protein productive value (PPV, 57.01–68.95%), lipid productive value (LPV, 63.02–75.15%) and energy productive value (EPV, 68.20–88.15%) increased significantly (P < 0.05) as linear response to increased dietary nucleotide from 0.5 to 2.5 g kg^?1 in the feed. With an increase in the dietary nucleotide, the uricase activity (654.29–827.63 U g^?1) and lactobacillus count to total count ratio (1.21–2.17) of crayfish fed the experimental diets increased significantly (P < 0.05). Crayfish fed the diets containing different levels of nucleotide (from 0.5 to 2.5 g kg^?1) had higher phenoloxidase activity (1.57–2.11 U min^?1) than that of control after air exposure challenge. At the levels tested, 2 g kg^?1 nucleotide in the diet was considered optimum for growth performance, digestibility and immune responses. It can be concluded that dietary nucleotide exerted positive effects on growth performance, feed utilization and accelerate crayfish immune response against air exposure challenge.     

The effects of seasonal,sex and size on the digestive enzyme activities in freshwater crayfish (Astacus leptodactylus Eschscholtz, 1823)

The effects of seasonal, sex and size on digestive enzyme activities of Astacus leptodactylus in natural habitat were investigated in the present study. The freshwater crayfish were sampled 584 individual as seasonally from Egirdir Lake. Ten male and 10 female individuals were sampled randomly from caught crayfish in each two different size ranges (4.5–7.0, 7.1–9.9 cm) and each season. The gastrointestinal tract, gastric, intestine and midgut gland were individually dissected on ice for enzyme analysis and stomach contents. At the end of the study, amylase activities were affected by interaction of season × sex × size in intestinal, season × sex in midgut gland. However, any interaction was not determined in amylase activities of the gastric. Lipase activities were affected by interaction of season × sex × size in intestinal and gastric, season × sex in midgut gland. The protease activities in each organ were affected by interaction of season, sex and size (p ? .05). In all organs, amylase and lipase activities were similar. However, the highest protease activity was in stomach while the lowest protease activity was the intestine. The protease activities were higher than amylase and lipase activities. There is a positive correlation between protease enzyme activities in gastric with gonad maturation and active feeding period. It can be said based on data of digestive system and high protease activity that A. leptodactylus is an omnivore species in need high protein. In addition, the reason for the low levels of lipase activity may be A. leptodactylus not prefer high fat foods or not fed high fat foods.     

The effect of dietary vitamin E on the pleopodal egg number of Astacus leptodactylus (Eschscholtz, 1823)

The effect of vitamin E on the pleopodal egg number of Astacus leptodactylus (Eschscholtz, 1823) was studied. Crayfish were fed 2% of their total wet weight daily with vitamin E supplemented diets and a control for 70 days. The vitamin E content of the control diet, diet 1, diet 2 and diet 3 were 20 mg kg^–1, 40 mg kg^–1, 80 mg kg^–1 and 160 mg kg^–1 respectively on a dry weight basis. Vitamin E levels of the control and experimental diets were analysed by High Performance Liquid Chromatography. Results showed that diets containing supplemental vitamin E were associated with an increase in the number of pleopodal eggs. The best result was obtained with diet 2 containing 80 mg kg^–1 supplemental vitamin E.     

Effect of dietary supplementation of calcium chloride on growth,survival, moulting frequency and body composition of narrow‐clawed crayfish,Astacus leptodactylus (Eschscholtz, 1823)

The effects of dietary calcium chloride (CaCl₂) concentration on the growth, survival, moulting and body composition of Astacus leptodactylus were studied. Diets were prepared using supplementation of 0 (control), 30, 60 and 120 g kg^?1 calcium chloride commercial trout larvae diet containing 50% protein and 12% lipid. Astacus leptodactylus larvae with an average total length of 22.0 ± 0.05 mm (TL) and weight of 0.53 ± 0.01 g obtained from eighteen ovigerous females collected from Seydisehir Sugla Dam lake in Konya, Turkey, were stocked in 0.2‐m² aquariums at a rate of 50 crayfish m^?2 and reared for 90 days. The experiments included four treatments (diets) with three replicates each. Calcium chloride exerted positive effects on growth, moulting frequency, feed efficiency and survival of narrow‐clawed crayfish. Crayfish fed with 60 g calcium kg^?1 calcium chloride‐supplemented diet exhibited the highest weight gain and specific growth rate (SGR) but the lowest survival rate (63.3%) (P < 0.05). There were no significant differences (P > 0.05) in mean moisture (803.5 g kg^?1) and protein content (177.0 g kg^?1) in crayfish tail meat. However, lipid values were between 3.8 and 11.6 g kg^?1 and significantly different among the diets (P < 0.05). Diet with 60 g kg^?1 calcium chloride is recommended for the best growth of freshwater crayfish.     

Antifungal effect of Origanum onites essential oil as an alternative to formalin in the artificial incubation of narrow‐clawed crayfish (Astacus leptodactylus Eschscholtz, 1823)

As alternative to formalin, the antifungal effect of a plant product [Origanum onites L. (Lamiaceae) oil] was investigated for use in the artificial incubation of narrow‐clawed crayfish (Astacus leptodactylus Eschscholtz) eggs. For this purpose, this study was conducted as two experiments. In experiment I, the eggs were artificially incubated for 40 days. In experiment II, juveniles were cultured to determine effects of O. onites oil on juveniles for 30 days. The experimental groups were as follows: formalin (3500 ppm for 15 min), O. onites oil (300 ppm for 15 min, 700 ppm for 2 min and 1000 ppm as a dip treatment 15 split‐second) and a control (no treatment). In the experiment I, the highest hatching rate (86%) and survival rate of stage II juveniles (80%) were observed in 1000 ppm dip group. These results were similar to that of formalin group (85% and 79%) respectively. The control group exhibited the lowest hatching rate (49%) and stage II rate (42%) compared with the 1000 ppm dip group and 3500 ppm formalin treatments. However, other concentrations (300 and 700 ppm) of O. onites showed toxic effects on the eggs and there was no hatching. In the experiment II, the survival rate and growth performance of the crayfish juveniles were similar in all groups. This study indicated that the 1000 ppm O. onites dip treatment could be a good alternative to formalin for improved egg hatchability in the artificial incubation of crayfish eggs.     

The effect of dietary n‐3 series fatty acids on the number of pleopadal egg and stage 1 juvenile in freshwater crayfish,Astacus leptodactylus Eschscholtz

The effect of dietary n‐3 series fatty acids on the number of pleopadal egg and stage 1 juvenile in freshwater crayfish, Astacus leptodactylus was investigated. Crayfish were fed with n‐3 series fatty acids supplemented diets and a control diet for 251 days. Control diet did not comprise additional n‐3 series fatty acids. However, D2, D3 and D4 groups were supplemented with n‐3 series fatty acids at 1%, 2% and 3% level respectively. Results showed the beneficial effects of dietary n‐3 series fatty acids on the production of pleopodal egg and stage 1 juvenile number. At the end of the experiment, pleopodal egg (from 177 to 234) and stage 1 juvenile number (from 167 to 225) increased significantly with increased dietary n‐3 series fatty acid level. In addition, an increase in dietary n‐3 series fatty acids led to an increase in number of pleopodal egg and stage 1 juvenile produced per gram of female crayfish weight. It can be concluded that the reproductive efficiency of A. leptodactylus (i.e., pleopodal egg and stage 1 juvenile number) can be improved in controlled hatchery conditions by adding n‐3 series fatty acid into the diet of this species.     

Effects of dietary antioxidants on oxidative stress,antioxidant defence and growth of freshwater crayfish Astacus leptodactylus (Eschscholtz, 1823) during the reproductive period in females

In this study, we examined the effects of dietary antioxidant vitamins [vitamin E (Vit E), vitamin C (Vit C) and vitamin A (Vit A)], astaxanthin (AX) and β‐carotene (βC) supplementation on oxidative stress [malondialdehyde (MDA)], antioxidant enzyme activities [superoxide dismutase (SOD), catalase, glutathione peroxidase (GSH‐Px)] and glutathione (GSH) levels in hepatopancreas, ovarian, muscle, gill tissues and survival rates (SR), live weight gain (LWG), specific growth rate (SGR) of Astacus leptodactylus during ovarian development. The EE, EC, EA, EAX and EβC groups were formed by addingClick here to enter text. Vit E, Vit C, Vit A, AX and βC to the diet respectively. The antioxidants did not have a significant impact on the values of SR, LWG and SGR. After 137 days, the MDA levels in the Control (C) group were statistically higher in the hepatopancreas, ovarian and muscle tissues according negative control (NC), EE, EC, EA, EAX and EβC groups. The SOD activities in ovarian, muscle and gill tissues and GSH levels in ovarian and muscle tissues were lower in the C group compared with the NC group, but GSH‐Px activities in hepatopancreas and ovarian tissues and GSH levels in gill tissues were higher. The MDA levels were statistically lower in all tissues of crayfish in experimental groups according to C group. The antioxidant enzyme activities and GSH levels changed according to tissue. The results showed that Vit E and AX should be supplemented in diets to increase the reproductive performance of crayfish, because Vit E and AX were of higher potential as antioxidants than other vitamins and carotenoids in ovarian tissues.     

Occurrence of Psorospermium sp. in several North American crayfish species, with comparative notes on Psorospermium haeckeli in the European crayfish, Astacus astacus

Psorospermium haeckeli is a thick-walled, unicellular organism widely reported in European astacid crayfish. Its taxonomic status and life cycle have not been elucidated. It is often referred to as a “parasite”, but conclusive evidence has yet to be found. Recent examination of two North American crayfish species, Procambarus clarkii and Procambarus zonangulus, confirmed its presence in the south-central USA (Louisiana) with morphologies that differ from that of P. haeckeli. This form had been previously reported from Orconectes virilis in southern Canada. We report here the presence of this North American form of Psorospermium in additional North American crayfish including Orconectes immunis and Orconectes rusticus from the northern USA (Minnesota and Wisconsin), Procambarus alleni and Procambarus fallax from the southern USA (Florida), and Pacifastacus leniusculus from the western USA. We also confirm this Psorospermium in O. rusticus from eastern Canada (Ontario). It was not, however, confirmed in several additional southern crayfish species including Cambarus diogenes, Cambarellus puer, Fallicambarus fodiens, and Orconectes palmeri. We describe the morphological forms of this Psorospermium and conclude that it is present in many crayfish species in North America.     

Incisor ridge modification of the mandibles in freshwater crayfish, Astacus leptodactylus

The differences in the ridge structure of the mandibles of different size Astacus leptodactylus (32–80 mm carapace length, CL) were investigated. The results showed that a modification occurs with an increase in size in the incisor ridge of mandibles in A. leptodactylus. The results also showed that A. leptodactylus possesses four different types of ridge structure in the mandibles. These are: (1) Incisor ridge with big teeth (dentate crenate), (2) Blade-like incisor ridge with numerous small teeth, (3) Blade-like ridge (toothless), (4) Blunt ridge. In conclusion, it is thought that the incisor ridge modification of the mandibles may cause the difference in the food choice of different size A. leptodactylus, because, crayfish possessing different ridge structures of the mandible may probably feed on different type of food.     

Meat yields in the introduced freshwater crayfish, Pacifastacus leniusculus (Dana) and Astacus leptodactylus Eschscholtz, from British waters

The freshwater crayfish industry in Britain is based on two species, Pacifastacus leniusculus (Dana) and Astacus leptodactylus Eschscholtz, which were introduced during the 1970s and 1980s. The former is widely cultivated but both are also established in the wild, from where they are harvested. Very few studies have been made of the meat yield in these two species and none on British populations. Two essentially wild populations were assessed for their meat yield. Due to its more massive claws male P. leniusculus had a higher meat yield than male and female A. leptodactylus and female P. leniusculus in both winter and summer months. Less difference was found between the yield of tail meat between the sexes and species. Compared with other studies, meat yield in the two British populations of P. leniusculus (11–15%) and A. leptodactylus (9–13%) would appear to be lower; possible reasons for this are discussed. However, expressing meat yield as a percentage of wet body weight, although useful for comparative purposes, can give conflicting results – examples of this are given. Meat yields from the claws of the two species indicated that positive allometric growth continued after sexual maturity.     

Effect of dietary n-3 series fatty acids on sperm production in the freshwater crayfish, Astacus leptodactylus (Eschscholtz) (Astacidae)

The objective of the present work was to evaluate the effects of three different rates of long chain n-3 polyunsaturated fatty acid (LC n-3 PUFA) on the sperm number of Astacus leptodactylus. The experiment was carried out with the four following treatments: control group (not supplemented LC n-3 PUFA), D1 (1 %), D2 (2 %) and D3 (3 %). The sperm number of A. leptodactylus was counted; the reproductive system was weighted; and the macroscopical analysis of the testes and vasa deferentia (DVD) were conducted. In addition, gonado-somatic index (GI) and testes index (TI) were also calculated. The results showed that there was a significant difference between the crayfish fed LC n-3 PUFA supplemented diets (D1, D2, D3) and control in mean sperm number (P < 0.05). The highest sperm number was found for the crayfish fed D3 (6.27 ± 0.14 × 10⁸ sperm/distal vas deferens section). The results also showed that the reproductive system of the crayfish fed D3 and D2 was significantly heavier than that of the crayfish fed the control and D1 (P < 0.05). On the other hand, there was not a significant difference in the testes weight and vasa deferentia weight between the crayfish fed the control and D1, and between the crayfish fed D2 and D3 (P < 0.05). GI of the crayfish fed D3 and D2 was significantly higher than that of the crayfish fed control and D1 (P > 0.05), but there was not a significant difference in the TI of the crayfish fed control, D1, D2 and D3 (P > 0.05). In conclusion, diets containing different levels of LC n-3 PUFA significantly increase the sperm number of A. leptodactylus, and they are crucial for the production of higher number of sperm in this species.     

A comparison of the growth and survival of two freshwater crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), under different temperature and density regimes

Growth experiments carried out with two juvenile crayfish species, Astacus leptodactylus Eschscholtz and Pacifastacus leniusculus (Dana), at different temperatures and densities highlighted the problem of cannibalism under conditions aimed at intensifying crayfish production. Cannibalism proved to be much lower in A. leptodactylus than P. leniusculus, suggesting that the former might be the better candidate for astaciculture. In the first of two population survival trials, A. leptodactylus showed a higher survival rate than P. leniusculus, with 26% of P. leniusculus surviving in the first replicate, compared to 42.3% of P. leniusculus, and 40.76% surviving in the second replicate, compared to 47.6% of P. leniusculus. The same trend was observed in the second experiment, with P. leniusculus showing survival rates of 48.5 and 55.3% (first and second replicates, respectively) in comparison to 65.2 and 68.2%, respectively, for A. leptodactylus. It is therefore highly likely that if P. leniusculus were to become established in Turkey, it would outcompete the native A. leptodactylus even if it were not to be devastated by the crayfish plague that has decimated the native species. The experiments also highlighted the problem of differential growth, with some juveniles hardly growing at all while others reached a relatively large size. The range in carapace length (CL) was 9–18 mm for A. leptodactylus and 8.5–18.5 mm CL for P. leniusculus at the end of the first experiment. While both species grew quickly, P. leniusculus hatched earlier, giving it an advantage over A. leptodactylus; consequently, by the end of the summer, the juveniles of the former were larger than those of A. leptodactylus. Specific growth rate values showed that the juveniles of the two species had similar growth rates. The results also revealed that growth was not significantly affected by density in both species at 15°C, but at 25°C, growth was significantly better at a density of 234 juveniles m⁻² than at 468 juveniles m⁻², and better at 468 juveniles m⁻² than at 937 juveniles m⁻² (P < 0.01 and P < 0.001, respectively). We conclude that P. leniusculus is a good candidate for aquaculture as it has a rapid growth rate and early hatching and maturity; however, its aggressive behavior may make it a less attractive proposition than A. leptodactylus, which is also fast growing but less aggressive. This study is a part of PhD study of M.M. Harlıoğlu, who is supported by Fırat University Elazığ, Turkey.     

A preliminary study on the use of mannan oligosaccharides (MOS) in freshwater crayfish, <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> Eschscholtz, 1823 juvenile diets

The effects of dietary mannan oligosaccharides (MOS) on the survival and growth of Astacus leptodactylus juveniles were evaluated. Experimental diets were prepared by using supplementation of 0 (Control), 1.5, 3.0, and 4.5 g MOS kg⁻¹ commercial trout larvae diet containing 43 g kg⁻¹ protein and 15.74 g kg⁻¹ lipid. A. leptodactylus juvenile with an average total length of 3.6 ± 0.46 cm (TL) and average weight of 1.25 ± 0.43 g was stocked in 0.2-m² aquariums at a rate of 50 crayfish/m² and reared for 60 days at 22.8°C. The experiment consisted of four treatments with three replicates each. Each aquarium contained ten crayfish. Crayfish juvenile fed with 0, 1.5, 3.0, and 4.5 MOS attained 6.15 ± 0.49, 5.94 ± 0.29, 7.34 ± 0.39, and 5.94 ± 0.27 cm final total length and 50, 56.67, 46.67, and 50% survival rates, respectively. Moreover, molting frequencies in 0, 1.5, 3.0, and 4.5 g kg⁻¹ MOS groups were detected as 44.44, 61.11, 83.33, and 38.88%, respectively. At the end of the experiment, a general enhanced growth performance (P < 0.05) and feed conversion ratio were observed in crayfish fed on the diet containing 3.0 g kg⁻¹. Crayfish juveniles fed with 3.0 g kg⁻¹ MOS had the highest final length (7.34 ± 0.39 cm), although their survival was the lowest (46.67%) compared to other treatments but not significant. Specific growth rates were significantly different (P < 0.05) among the treatment groups at the end of the 60-day experiment. There were no significant differences (P > 0.05) in percentage moisture, protein, and ash (wet-weight basis) in the tail meat of A. leptodactylus juvenile among treatments (diet) that averaged 82.3, 16.1, and 1.2%, respectively. However, lipid value was significantly different among the diets P < 0.05), with values between 0.13 and 0.32. From the current results, it could be advised to use MOS at the rate of 3.0 g kg⁻¹ in A. leptodactylus juvenile diets.     

Shifting the natural spring–summer breeding season of the Australian freshwater crayfish Cherax quadricarinatus into the winter by environmental manipulations

Ninety sexually mature Cherax quadricarinatus females were exposed to various combinations of photoperiod and temperature for 2 months during the summer. Females were randomly assigned to either “winter” “semi-winter” or “summer” simulation treatments. In the “winter” treatment, crayfish were exposed to a simulated winter photoperiod (gradual decrease from 14L:10D to 10L:14D, 4 weeks at short day length followed by gradual increase to 14L:10D) and temperature (gradual decrease from 27 to 15 °C, held for 4 weeks, and then gradual increase to 27 °C). In the “semi-winter” treatment, crayfish were exposed to a simulated winter photoperiod and a summer temperature (27–29 °C). In the “summer” treatment, the crayfish were exposed to summer water temperatures and a photoperiod of 14L:10D. Following the 2 months of conditioning, the females were stocked for 7 months in small groups with males under environmental conditions similar to those of the “summer” treatment. All females were individually tagged and molting and spawning events were monitored. Females exposed to “semi-winter” conditioning in the summer, demonstrated a threefold increase in the rate of first spawning during the winter (December–February) compared with the other females. Crayfish breeders can easily implement these findings since shifting the breeding season into the winter only requires shortening of the photoperiod in the summer. The stocking of ponds in the spring with large nursed juveniles that hatched from eggs spawned in the winter, would allow the attainment of market size at the end of the limited growout season in temperate zones.     

Effect of serotonin injection on the reproductive parameters and haemolymph methyl farnesoate level in the narrow‐clawed crayfish Pontastacus leptodactylus (Eschscholtz, 1823)

The effects of serotonin injection (1, 5 and 10 µg/g body weight) on spermatozoal production, vas deferens index (VDI), hepatosomatic index (HSI), testicular index (TI), gonado‐somatic index (GSI), ovarian egg number, total protein, methyl farnesoate (MF) levels of haemolymph, amino acid and fatty acid profiles of hepatopancreas were evaluated in Pontastacus leptodactylus. In male P. leptodactylus, the highest spermatozoal number (9.3 × 10⁶ ± 1.2) and MF level (0.66 ± 0.06 ng^?1 ml) were observed after injection of 10 µg/g of serotonin (p < .05). Serotonin injection, however, did not significantly affect the reproductive parameters in female P. leptodactylus (p > .05). It was also found that serotonin injection caused an increase in the level of MF in male P. leptodactylus but a reduction in female P. leptodactylus (p < .05). Therefore, a sex‐dependent response to serotonin could exist for MF synthesis in P. leptodactylus. Serotonin injection did not affect the total protein, amino acid and fatty acid profiles in the hepatopancreas of male P. leptodactylus (p > .05). It can be concluded that serotonin injection affects the reproductive parameters such as spermatozoal production, VDI, TI, GSI, HSI and haemolymph MF levels in P. leptodactylus.     

我国淡水渔业的发展现状及存在问题浅议

我国淡水渔业的发展现状及存在问题浅议贾敬德（中国水产科学研究院长江水产研究所）九十年代以来,我国的水产业,特别是淡水渔业,进入快速发展的时期。这种发展,表现在渔业生产上,主要是产量的增加,质量的提高,表现在科学技术上,就是多方面的水产科技成果转化为生...