Muzaffer Mustafa Harlıoğlu

The present situation of freshwater crayfish, Astacus leptodactylus (Eschscholtz, 1823) in Turkey

Abstract The only native crayfish species in Turkey, Astacus leptodactylus, is widely distributed in lakes and ponds in many parts of the country. Its distribution area was considerably expanded in Turkey after 1985 because of its commercial importance and declined catches from traditional good fisheries. Although consumption of A. leptodactylus has always been very low in Turkey, it was exported to western Europe until 1986. Due to over-fishing, pollution and a disease (crayfish plague), the total production decreased dramatically to 200 from 5000 tonnes annually. In recent years (1991–1998), there has been a gradual increase in the production of crayfish in Turkey from 320 to 1500 tonnes, but plague is still present.

Threat of non-native crayfish introductions into Turkey: global lessons

Introductions of crayfish species from their home range to new environments have been carried out in many parts of the world. The most important introduced crayfish species are Procambarus clarkii, Pacifastacus leniusculus, Cherax destructor, C. quadricarinatus, Orconectes limosus, O. rusticus and Astacus leptodactylus. The environmental impact of crayfish introductions can be positive, negative or neutral. However, native crayfish populations in Europe have been negatively affected by introductions of non-indigenous crayfish species from America. Negative effects of non-native crayfish introductions included displacement of native crayfish species, transfer of disease (crayfish plague), consumption of fish eggs, reduction of fish stocks, consumption of large amounts of macrophytes, indirect and direct effects on other invertebrates and upsetting production in rice fields. As a result of non-native crayfish introductions, the natural harvest and crayfish industry in Europe have been severely affected. Large quantities of Turkish A. leptodactylus were harvested (approximately 7,000 tonnes annually) and exported to Europe before the crayfish plague was observed in these populations. The total harvest of A. leptodactylus in Turkey reduced dramatically to 320 in 1991 after the plague. Therefore, although Turkey currently has no known non-native crayfish species, there is a threat of non-native crayfish introduction in order to increase crayfish productions and subsequent harvest. The North American spiny-cheek crayfish, O. limosus, has been spreading quickly down the River Danube and could soon reach neighboring countries including Turkey. The North American signal crayfish, P. leniusculus is known from Greece and could be a threat to native stocks if it is introduced into Turkey for aquaculture. Additional threats may come from the release of other North American species, which are widely available through the aquarium trade. We conclude that the spread of non-native crayfish introductions throughout Turkey will increase local problems, because introductions of non-native crayfish in many parts of the world have been known to have caused important reductions in population density and numbers of native crayfish species. Furthermore, freshwater ecosystems may be altered by such introductions and the economic viability of native crayfish species fisheries could be severely reduced in Turkey.

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.

Status of Freshwater Crayfish Distribution in Thrace Region of Turkey

This review focuses on the present distribution of two crayfish species: narrow-clawed crayfish Astacus leptodactylus Eschscholtz and stone crayfish Austropotamobius torrentium (Schrank, 1803) in Thrace region of Turkey. The only known native (indigenous) freshwater crayfish species of Turkey is A. leptodactylus. It is found at more sites than A. torrentium. On the other hand, A. torrentium is only found in Thrace region of Turkey. The first population of A. torrentium was observed in Velika River in 1995. In 2006, the second population of A. torrentium was found in Madara Brook in the region, but the abundance of A. torrentium in Madara Brook was very low in comparison to Velika River. Moreover, further studies carried out in some water resources near the population of A. torrentium, such as De[vgrave]irmen Brook, Poyralı Brook, and Hasköy Brook confirmed that no other populations of this species are present in the region at present. Therefore, it can be concluded that A. torrentium is only present in the northwest of Marmara river basin (Istaranca Mountain Part) and A. leptodactylus is widely distributed throughout the places located to the south of Marmara river basin, and Istaranca Mountain might be a border line that separates A. leptodactylus and A. torrentium populations. Moreover, except the presence of these two species, no other crayfish species are found in the Thrace region of Turkey at present.

An investigation on the sperm number and reproductive parameters of males in wild caught freshwater crayfish (Astacus leptodactylus, Eschscholtz)

In the present study, the sperm number of wild caught Astacus leptodactylus was counted in the beginning of reproduction season. In addition, the reproductive system, testes, and vasa deferentia were weighed, and gonado-somatic index and testicular index were calculated. Twenty-five adult males of A. leptodactylus were used for the study. Significant linear regressions were found between body length (and weight) and sperm count, reproductive system weight, testes weight and vasa deferentia weight ( P < 0 . 05 ). The mean sperm number of vas deferens for the size range of 41-56 mm carapace length crayfish was 5.72 ± 4.54 × 109 sperm/distal vas deferens (DVD) section. Sperm number ranged from 4 × 108 to 8.5 × 109 sperm/DVD section. The results revealed that an increase in body weight causes an increase in sperm number. For example, mean sperm number was 3.87 ± 2.87 × 109 for the weight range of 15-24 g crayfish, 5.01 ± 2.62 × 109 for the weight range of 25-35 g crayfish and 7.37 ± 2.87 × 109 for the weight range of 36-42 g crayfish. In conclusion, this study provides some data on the male reproduction characters and needs to be improved with details about the reproductive performance of males (i.e., sperm number and quality) in order to reach a maximum reproductive efficiency in captivity.

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.

Visibility of precursors of the gonopods in a freshwater crayfish, Astacus leptodactylus Eschscholtz, 1823 (Decapoda, Astacidae)

Astacus leptodactylus Eschscholtz, 1823 is an important, marketable species of crustacean, consumed intensely as a luxury food in many countries. Because A. leptodactylus is less cannibalistic than other crayfish species, is more fecund, and has a fast growth rate, it is accepted as a considerably suitable crayfish for culturing in extensive pond systems. Information on the reproductive biology and anatomy of crayfish is important for developing suitable production methods. Sex recognition may also be essential in separating males and females in crayfish rearing (i.e., to prevent cannibalism, males grow faster than females). Although male reproductive system morphology and spermatophore formation in crayfish, including A. leptodactylus , have been studied in detail, this study is the first to demonstrate the visibility of precursors of the gonopods and, thus, the actual presence of gonopods, which of course determine the male sex, in a freshwater crayfish. The present study shows that the first signs of secondary sexual characters (i.e., precursors of the gonopods) can be distinguished in the form of small tubercles on the first abdominal somite in male stage 4 juveniles, and the gonopods themselves are distinguishable in male stage 5 juveniles in A. leptodactylus . In conclusion, sex differentiation in A. leptodactylus can be realized already in stage 4 juveniles. Further studies should be carried out on the presence and shape of precursors of gonopods in stage 4 and gonopods in stage 5 juveniles of species of astacid crayfish in order to facilitate solving taxonomic problems in the family Astacidae.

The Status of Freshwater Crayfish (Astacus leptodactylus Eschscholtz) Fisheries in Turkey

Although there have been fluctuations among years, the harvest of A. leptodactylus in Turkey has increased steadily after 1995. Prior to this increase, the harvest was under the pressure of over-catching, water pollution, and a fungal disease (Aphanomyces astaci Schikora), which was first observed in Turkey in 1984. However, the harvest of A. leptodactylus in Turkey has started to decrease again since 2005. The harvest decreased from 2,317 tonnes in 2004 to 809 tonnes in 2005 and to 797 tonnes in 2006. Furthermore, the harvest decreased to 750–760 tonnes in 2007. An explanation for the reduction in crayfish harvest is not known for all populations. No published reports have attributed the massive mortalities of crayfish due to the fungal disease. Some populations are under the pressure of over-harvesting in some years. The shortage in A. leptodactylus harvest in Turkey, which is one of the main exporters of A. leptodactylus to Europe, has led to the tendency of European consumers to import Pacifastacus leniusculus or Procambarus clarkii from China and America. To increase crayfish production in Turkey, the idea of introducing non-native crayfish species into freshwaters may be encouraged, but these introductions may cause a worse situation because of the well-known adverse effects of non-native crayfish introductions throughout the world. Therefore, government and public authorities in Turkey should focus on a solution to the decrease in crayfish harvest in Turkey, and conservation and management studies of crayfish populations are also critically needed.

Effects of 17β-estradiol injection on the reproductive efficiency of freshwater crayfish, Astacus leptodactylus (Eschscholtz, 1823)

ABSTRACT The effects of 17β-estradiol injection (10−7mol/crayfish) in adult female Astacus leptodactylus on the reproductive efficiency (i.e., pleopodal egg and stage 1 juvenile numbers) were investigated. In addition, hepatosomatic index, gonodosomatic index, and 17β-estradiol (E2) levels of crayfish ovary, hepatopancreas, and heamolymph before and after injections were also determined. Results showed that E2 injection to females enhances the reproductive efficiency of A.leptodctylus. E2 injection significantly increased pleopodal egg and stage 1 juvenile numbers, GSI, HSI, and concentrations of E2 in heamolymph, ovary, and hepatopancreas. However, E2 injection did not accelerate time of mating and proportion of pleopodal egg-berried females at the first week of reproduction season in this species. This study highlights that to improve the reproductive efficiency of A.leptodctylus by using hormones to regulate the ovarian cycle, E2 should be used at least 1.5 months before the commencement of the breeding season.

Optimization of the incubation time and temperature for spermatozoa extraction in freshwater crayfish Pontastacus leptodactylus (Eschscholtz, 1823)

Determination and control of spermatozoa quality in crustacean aquaculture is an important issue for successful and controlled reproduction. Investigation of spermatozoa number in spermatophores is a basic and common parameter for determining the reproductive quality in farmed decapods. In the present study, spermatozoa extraction from spermatophores located in the ductus deferens was conducted in Pontastacus leptodactylus using different incubation times and temperatures. The results indicate that the duration of incubation and temperature affected (P < 0.05) spermatozoa extraction. Greater temperatures (40 and 75 °C) resulted in a reduction (P < 0.05) in number of extracted spermatozoa. In contrast, more spermatozoa were extracted when the 4 and 23 °C temperatures were imposed. After 4 h of incubation, the number of extracted spermatozoa were greatest in number at 23 °C. In conclusion, the greater numbers of crayfish spermatozoa can be obtained when the ductus deferens containing spermatophores is incubated at 23 °C for 4 h as compared with other temperatures and incubation durations. The results of present study are useful for assessing spermatozoa quality in aquaculture as well as the extraction of spermatozoa for research purposes.