Size and structure of crayfish (Astacus astacus) populations on different habitats in Finland

The many inland waters in Finland make crayfish production an important potential resource. The rational utilization and management of this resource requires knowledge of the size and structure of the crayfish populations. The difficulties often encountered in catching crayfish complicate population studies. Mark-recapture and electric fishing have been used in the studies. The number of adult crayfish measuring more than 70 mm in a 4-ha lake was estimated at 620, and the number in a 13-ha lake at 3 480. In the lakes, the density of adult crayfish was around 0.6–1.4 m^–2 and in one stream studied about 2.5 m^–2 rising to several individuals per m² in the best biotopes.     

The artificial incubation of crayfish eggs: review and report from an experimental study concerning the effects of offspring origin (maternal or artificial incubation) on the survival and growth of juvenile signal crayfish (Pacifastacus leniusculus, Astacidae)

The development of artificial incubation techniques in astacid crayfish has attracted attention from scientists in many countries ever since the nineteenth century. It is only in the last few years that these techniques, along with studies on egg storage and transport, have provided reliable options for improving the reproductive phase in farming. The juveniles produced need to be reared until they reach a sufficient size both for restocking and for growing purposes. In view of the current level of knowledge of rearing juvenile astacids, two 80-day experiments were carried out under controlled conditions to compare the survival and growth of Stage 2 juvenile signal crayfish (Pacifastacus leniusculus) from two origins: maternal or artificial incubation. In the first experiment, three treatments were tested: juveniles from artificially incubated eggs with formaldehyde treatments, juveniles from maternal incubation and a mixture from both origins (50% each). Survival rates ranged from 87.8% to 93.3% with no significant differences among treatments. Crayfish from artificial incubation grew significantly faster (11.47 mm carapace length (CL), 373.80 mg weight) than crayfish from maternal incubation. In the second experiment, a bifactorial design included four treatments: the crayfish was derived from artificial or from maternal incubation and was fed once a day or twice a day. Final survival rates ranged from 68.89% to 77.78%, with no significant differences among treatments. Crayfish from artificial incubation grew significantly faster than crayfish from maternal incubation. The highest CL (14.54 mm) and weight (780.13 mg) were reached by the juveniles from artificial incubation that were fed once a day. No significant differences were found between the two feeding frequencies. Results showed that artificial incubation with formaldehyde treatments had no harmful effects and made it feasible to get a better performance from the juveniles obtained.     

Invasive American crayfish <Emphasis Type="Italic">Pacifastacus leniusculus</Emphasis> (Decapoda: Astacidae) in the Morava River (Slovakia)

The signal crayfish, Pacifastacus leniusculus (Dana, 1852), was recorded in the Slovak-Austrian stretch of the Morava (March) River in the Záhorie region in August 2006. This is the first confirmed record of a non-indigenous crayfish species of American origin in Slovakia. Most likely, signal crayfish were intentionally released to the river by Austrian fishermen, or invaded from adjacent water bodies in Austria. As this species has a substantial invasive capability and is a potential vector of the crayfish plague pathogen, it represents a threat to the native crayfish species and its spread should be monitored. Its invasion upstream to the territory of the Czech Republic is not unlikely in near future.     

Winter movements and activity of signal crayfish Pacifastacus leniusculus in an upland river,determined by radio telemetry

Radio-telemetry was used to study the late autumn and winter movements of twenty adult signal crayfish Pacifastacus leniusculus (32.9–63.8 mm carapace length) an introduced exotic crayfish species, in the upland River Wharfe, northern England. The distances moved during the study varied greatly between individuals (0–328 m). Movements were generally sporadic; crayfish would remain in one position for several weeks and make occasional movements to new locations. Total distances travelled, linear range and ranging area did not differ significantly between males and females. The distance travelled in upstream and downstream directions did not differ significantly and there was no correlation between distance travelled and crayfish size. Several high flow events occurred during the study, but these did not cause any mortality or apparent displacement of crayfish downstream, suggesting that this is not a significant factor in downstream dispersal or mortality of adults of this invasive crayfish species in winter. A marked reduction in large-scale movements occurred in mid-December which coincided with a decline in water temperature. There was a less distinct pattern in local activity which was strongly correlated with water temperature and varied before and after mid-December.     

Immigration rates of signal crayfish (Pacifastacus leniusculus) in response to manual control measures

1. Crayfish are amongst the most frequently introduced non‐native aquatic organisms, with well‐documented negative effects on a large number of freshwater taxa. Many crayfish‐control strategies make use of manual removal by trapping, a method known preferentially to remove the largest individuals, leaving the juvenile population almost entirely untrapped. 2. A predicted outcome of trapping bias in riparian habitats is that removed individuals could be replaced by large crayfish immigrating from surrounding, untrapped, areas. We tested the hypothesis that removal by trapping of American signal crayfish from a U.K. river would result in increased rates of immigration, and increased distances moved, of crayfish from untrapped areas. 3. We studied four stretches of the River Windrush each 1 km in length and divided into three sections; a 250‐m long upstream section, a 500‐m middle section and a 250‐m downstream section. At two sites (removal sites), signal crayfish were trapped and removed from the 500‐m middle sections; at the other two (non‐removal), they were marked and returned. All crayfish captured in the upstream and downstream sections were marked and returned. 4. Probability of capture was higher for larger individuals with both chelae intact, and larger crayfish were more likely to immigrate from the upstream and downstream sections into the middle. The percentage of captured crayfish immigrating into the middle sections was the same (3.7%) in both removal and non‐removal sites. However, the mean distance that crayfish moved when immigrating was significantly greater at removal sites (239 m) than at non‐removal sites (187 m). 5. These results imply that removal of large individuals may have reduced the potential for interference competition by increasing the relative competitiveness of the immigrating individuals and permitting them to make larger movements. Consequently, the impact of manual removal strategies, both on the signal crayfish population and other biota affected by them, is likely to be reduced at the point of removal, but to extend at least 200 m beyond the trapped length of river.     

Structural and functional properties of the mechanoreceptors and chemoreceptors in the anterior oesophageal sensilla of the crayfish,Astacus astacus

Summary The anterior oesophageal sensilla (AOS) of Astacus astacus are short cuticular cylinders with a terminal pore. Three sensory cells belong to each AOS, two of them having a dendritic ciliary segment of about 2 m length (A-cells), the third having this segment about 12 m long (B-cell). The ciliary A-tubules in the B-cells only possess arms and an electron-dense core. The dendritic inner segments of the A-cells terminate 3–6 m distal of the B-cells. The dendritic tips of most A-cells are connected by desmosomes. All dendritic inner segments contain a ciliary rootlet and are accompanied by a scolopale within the innermost enveloping cell. There are four enveloping cells, three of which form thin subepithelial columns together with the enclosed sensory cells. Recordings from the posterior branch of the anterior oesophageal nerve containing the axons of the AOS revealed the presence of three types of sensory cells, two being chemosensitive and one mechanosensitive. One chemoreceptor is specifically sensitive to nicotinamide, but responded also to -NAD, 6-aminonicotinamide, nicotinamide methyl esther and nicotin. It was blocked by p(4)-acetylpyridine. The second chemoreceptor responded only to crayfish gastric fluid. The mechanoreceptors reacted to stretch of the oesophageal wall adapting only slowly to maintained stimuli. It is assumed that the A-cells are the chemosensitive cells and the B-cells the mechanosensitive ones. The latter show only a small number of modality-specific characteristics. Several structural features appear to be correlated with the location of the AOS within a flexible surface, which undergoes considerable dilation.Supported by the Deutsche Forschungsgemeinschaft (H.A.:SFB 4/G1; H.H.: HA 1201/1-4)     

New records and distributions of two North American branchiobdellidan species (Annelida: Clitellata) from introduced signal crayfish, <Emphasis Type="Italic">Pacifastacus leniusculus,</Emphasis> in Japan

This is the first report of two North American branchiobdellidans, Sathodrilus attenuatus Holt, 1981, and Xironogiton victoriensis Gelder and Hall, 1990, on the signal crayfish, Pacifastacus leniusculus (Dana, 1852) introduced into Japan from the Columbia River system, northwestern North America. Signal crayfish from 12 localities in eastern and northern Hokkaido, Japan, were examined and each supported S. attenuatus. In addition, an individual of this species was found on preserved material from Ishikawa Prefecture, central Honshu. All of these branchiobdellidans reported in Hokkaido most probably came from the original population of signal crayfish introduced into Lake Mashu, Hokkaido, Japan, in 1930. It is suggested that the use of non-pathogenic branchiobdellidans, when present, provides an easy method for tracing the spread of crayfishes around Japan and could also be applied in other countries and continents. Specimens of X. victoriensis were only found on crayfish in a stream at Akashina in Nagano Prefecture, central Honshu, Japan. Although the signal crayfish appears to be displacing the endemic Japanese crayfish, C. japonicus, no native branchiobdellidans were found on any of the introduced signal crayfish examined.     

Ultrastructure of the Y-organ of Astacus astacus (L.) (Crustacea) in relation to the moult cycle

Summary The electron microscopical investigation of Y-organs of Astacus astacus revealed that during intermoult (stage C) the cytoplasm is poorly developed and that it increases at premoult (stage D). It then shows the typical signs of steroid production, namely agranular endoplasmic reticulum and mitochondria of the tubular type. Furthermore, a larger type of mitochondria with a regular pattern of internal structure is described.Supported by Sächsische Akademie der Wissenschaften zu LeipzigWe are grateful for technical assistance to Mrs. B. Cosack und Mrs. A. Schmidt     

The harvest of freshwater crayfish, <Emphasis Type="Italic">Astacus leptodactylus</Emphasis> (Eschscholtz, 1823) in Turkey

Astacus leptodactylus is naturally and widely distributed in lakes, ponds and rivers throughout of Turkey. It has also been stocked in many freshwater systems in Turkey to establish new populations and to restore crayfish stocks devastated by the plague (Aphanomyces astaci) and some other reasons (i.e., farming and culinary purposes). Human consumption of A. leptodactylushas always been very low in Turkey; therefore, it was exported mainly to Europe until 1986. A plague was observed in 1985 in Eğirdir, Apolyont, Sapanca and Manyas lakes which included the main harvest areas, and the fishery was lost within 2 years. Consequently, crayfish harvest was banned in all populations to control the plague. Because of the plague, over-fishing and pollution, the harvest of A. leptodactylusin Turkey declined from approximately 5000 (1984) to 200 (1991) tons annually. In 2000s, there has been a gradual increase in the rate of harvest of A. leptodactylusin Turkey, reaching approximately 1600–1900 tons annually, but the plague is still observed in this species at certain localities. The present study reveals that A. leptodactylus in Turkey needs professional support for recovery, because the present harvest of A. leptodactylusis still nearly 20% of the crayfish catch in 1980s.     

Silicon amelioration of aluminium toxicity in teosinte (Zea mays L. ssp. mexicana)

The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al³⁺ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]_mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]_mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]_mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]_mono. In solutions with similar [Al]_mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.     

Relation of potassium uptake to proton transport and activity of hydrogenases in Escherichia coli grown at low pH

Escherichia coli grown under anaerobic conditions in acidic medium (pH 5.5) upon hyperosmotic stress accumulates potassium ions mainly through the Kup system, the functioning of which is associated with proton efflux decrease. It was shown that H⁺ secretion but not glucose-induced K⁺ uptake was inhibited by N,N′-dicyclohexylcarbodiimide (DCC). The inhibitory effect of DCC on the H⁺ efflux was stronger in the trkA mutant with defective potassium transport. The K⁺ and H⁺ fluxes depended on the extent of hyperosmotic stress in the absence or presence of DCC. The decrease in external oxidation/reduction potential and H₂ liberation insensitive to DCC were recorded. It was found that the atpD mutant with nonfunctional F₀F₁-ATPase produced a substantial amount of H₂, while in the hyc mutant (but not the hyf mutant defective in hydrogenases 3 (Hyd-3) and 4 (Hyd-4)) the H₂ production was significantly suppressed. At the same time, the rate of K⁺ uptake was markedly lower in hyfR and hyfB-R but not in hycE or hyfA-B mutants; H⁺ transport was lowered and sensitive to DCC in hyf but not in hyc mutants. The results point to the relationship of K⁺ uptake with the Hyd-4 activity. Novel options of the expression of some hyf genes in E. coli grown at pH 5.5 are proposed. It is possible that the hyfB-R genes expressed under acidic conditions or their gene products interact with the gene coding for the Kup protein or directly with the Kup system.     

Early death at medium acidification and survival after low pH adaptation inCryptococcus neoformans

WhenCryptococcus neoformans was grown in yeast nitrogen base (YNB) supplemented with 0.5% glucose, the medium was acidified to below pH 3 during the exponential growth phase, which caused early growth-phase death in susceptible strains. Even in resistant strains, 30–70% cells died if incubated for 2 d in YNB supplemented with 1.5% glucose, whereas the remaining cells survived long. Two types of fatal alterations have been observed in dead cells. In the first type, release of cytoplasm occurred through weakened parts of the cell wall; structures attached to cell walls of dead cells were shown to be rich in proteins by FITC staining, indicating their cytoplasmic origin. In the second type, cells shrank distinctly with no sign of wall rupture. The shrinkage may be due to dysfunction of the plasma membrane at low pH. The mechanism of cell survival in medium below pH 3 was also examined. Aniline blue alone, or calcofluor together with methylene blue, allowed cell wall glucan or chitin and dead cell cytoplasm to be stained simultaneously. In the later stages of incubation, cells showing bright staining for cell wall glucan and chitin emerged. These changes in cell wall synthesis could be considered as an adaptation mechanism to acidification of the medium, because such cells survived longer than cells showing no change in the cell wall staining pattern.     

Tolerance of low pH exposure by the eggs of Odonata (dragonflies and damselflies)

The development times and hatching success of the eggs of four species of Odonata (Ischnura verticalis, Lestes congener, Libellula lydia, and Sympetrum vicinum) were unaffected by exposure to soft water at pH 5.1 and 3.5. Tolerance of low pH, soft water conditions by Odonata eggs may in part account for the widespread distribution of Odonata in potentially acid-stressed regions.     

Appearance and innervation of CHH-producing cells in the eyestalk of the crayfish Astacus leptodactylus examined after tracing with Lucifer Yellow

Summary By injection of the fluorescent dye Lucifer Yellow into individual Crustacean Hyperglycemic Hormone (CHH)-producing cells, the shape of these neurosecretory cells in the eyestalk of the crayfish Astacus leptodactylus can be traced. A highly fluorescent perikaryon gives rise to an axon that can be followed by the fluorescent label to the neurohemal region, the sinus gland. The proximal part of that axon sends out extensive branches into the neuropil of the medulla terminalis. Electron-microscopic investigations reveal synaptic input to these axonal ramifications.     

Ontogeny of the antennal glands in the crayfish Astacus leptodactylus (Crustacea, Decapoda): anatomical and cell differentiation

The ontogeny of the antennal glands was studied during the embryonic and post-embryonic development of Astacus leptodactylus. The future glands arising from undifferentiated columnar cells were detectable at the metanauplius stage EI 150 m (EI: eye index; approximately 440 m at hatching). The tubule and labyrinth differentiated in embryos at EI 190 m, and the bladder and coelomosac at EI 250 m. At EI 350 m, the tubule lengthened and divided into proximal and distal sub-regions. In later stages, the gland retained the same morpho-anatomy but the differentiation and size of each part increased. The cells of the coelomosac displayed the cytological features of podocytes in late embryonic development at EI 440 m. Only small apical microvilli and a few mitochondria were observable in the labyrinth cells at EI 250 m; by EI 440 m, these cells presented well-shaped apical microvilli, formed bodies, basal infoldings and mitochondria. In the cells of the tubules and bladder, mitochondria and basal infoldings occurred at EI 440 m and EI 250 m, respectively. The differentiation of the tubules and bladder cells suggested that they were involved in active transport at EI 440 m. Following hatching, the differentiation of the cells and the size of the glands increased. The ontogeny of the antennal glands thus starts in early embryos, the specific cellular functional features being differentiated in the various parts of the glands by EI 440 m. The antennal glands are probably functional just before hatching, i.e., before the juveniles are confronted with the low osmolality of freshwater.Thanks are due to the University of Tarbiat Modarres and Ministry of Science, Research and Technology, Islamic Republic of Iran, for financial aid and support. Special thanks are also extended to the Société Française dExportation des Ressources Educatives (SFERE) for a scholarship to S.K.     

Influence of pH,exchangeable aluminium and 0.02M CaCl2-extractable aluminium on the growth and nitrogen-fixing activity of white clover (Trifolium repens) in some New Zealand soils

The effects of soil acidity on the growth and N₂-fixing activity of white clover in seven acid topsoils and subsoils of New Zealand were investigated using a glasshouse experiment.The application of phosphate (Ca(H₂PO₄)₂) to the soils resulted in very large increases in white clover growth on all soils. The application of phosphate, as well as increasing P supply, also decreased 0.02M CaCl₂-extractable Al levels, but had little effect on exchangeable Al levels.Where adequate phosphate was applied, increasing rates of lime (CaCO₃) resulted in increased plant growth on most soils. N₂[C₂H₂]-fixing activity was increased by the first level of lime for one soil, but generally remained approximately constant or declined slightly at higher rates of lime. Up to the point of maximum yield, white clover top weight was more highly correlated with 0.02M CaCl₂-extractable soil Al than with exchangeable Al or pH. At pH values greater than 5.5, plant yield declined on some soils, apparently because of Zn deficiency. The data suggest that white clover is unlikely to be affected by Al toxicity at 0.02M CaCl₂-extractable Al levels of less than about 3.3 g g^–1. However, there were differences between soils in apparent plant tolerance to 0.02M CaCl₂-extractable Al, which appeared to be caused by differing C levels in the 0.02M CaCl₂ extracts.     

Response of Lotus rhizobia to acidity and aluminium in liquid culture and in soil

Measurements of multiplication in liquid culture indicated that fast-growing Lotus rhizobia (Rhizobium loti) were tolerant of acidity and aluminium (at least 50 μM A1 at pH 4.5). Slow-growing Lotus rhizobia (Bradyrhizobium sp. (Lotus)) were less tolerant of acidity but equally tolerant of A1. Both genera were able to nodulateLotus pedunculatus in an acid soil (pH 4.1 in 0.01M CaCl₂) and the slow-growing strains were more effective than the fast-growing strains in this soil over 30 days.     

Protoplasts to plants of Gentianaceae. Regeneration of lisianthus (Eustoma grandiflorum) is affected by calcium ion preconditioning,osmolality and pH of the culture media

A reliable method has been developed for regeneration of whole plants from isolated protoplasts of five cultivars of lisianthus,Eustoma grandiflorum (Griseb.) Schinners (Gentianaceae). Protoplasts were isolated from either cotyledons or leaves and cultured in agarose beads surrounded by liquid V-KM media containing 5.37 µM 1-naphthyleneacetic acid (NAA) and 2.28 µM zeatin. When microcalli were approximately 1 mm in diameter, the agarose beads were transferred to shoot regeneration media containing 0.1 µM indolebutyric acid (IBA) and 4.44 µM 6-benzylaminopurine (BAP). Shoots were produced from the calli during several sub-culture periods. Protoplast viability and the subsequent regeneration of plants were dependent on calcium levels and growth regulator presence in thein vitro seed germination media, on the osmolality of the protoplast purification solution, and osmolality increase and pH of the culture media. Shoots were rooted in Murashige & Skoog (1962) media containing 5.71 µM indole-3-acetic acid (IAA). Plantlets derived from protoplasts of five lisianthus cultivars (Fresh White, Hakusen, Miss Lilac, Fresh Purple and Doremi Wine Red) have been successfully transferred to the glasshouse.     

The ultrastructural basis of steroid production in the Y-organ and the mandibular organ of the crabs Hemigrapsus nudus (Dana) and Carcinus maenas L.

Summary The ultrastructure of the steroid producing Y-organ and the mandibular organ of the crustaceans Hemigrapsus nudus and Carcinus maenas has been studied with reference to the well investigated steroid secreting cells (SSC) of mammals. In accordance with the most important characteristic of mammalian SSC, abundant SER could be shown in the Y-organ, where it is unevenly distributed. The amount of SER seems to vary in correlation with the secretion of moulting hormone during the moult cycle. Most Y-organ cells contain a great number of mitochondria of the tubular type, another important characteristic of mammalian SSC. The ultrastructure of the mandibular organ of C. maenas differs considerably from that of the Y-organ. Some SER was found, mitochondria of unusual shape and size were conspicuous. No definite conclusion as to the function of the mandibular organ is yet to be drawn.Dedicated to Prof. Dr. Peter Karlson on the occasion of his 60th birthdaySupported by the Deutsche Forschungsgemeinschaft, grant Ad 24/4We wish to thank Dr. A. Owczarzak, Oregon State University, Corvallis, Oregon, for providing the facilities for our work with H. nudus and Thomas Gallenstein for many helpful discussions of technical problems     

Effects of pH and heavy metal concentrations in solution culture on the proton release,growth and elemental composition ofAlyssum murale andRaphanus sativus L.

The proton release by a species that can hyperaccumulate nickel (Alyssum murale) and by a non-accumulator (Raphanus sativus L.) was studied at different pH and heavy metal concentrations in solution culture. Both factors influenced the growth and composition of the plants.A. murale was more sensitive than radish to a decrease of pH from 7.0 to 6.0 in the growth medium; plant yield and proton production diminished with decreasing pH. However, yields and proton production of radish only decreased at pH 5.5. The differences in the amounts of protons produced between the hyperaccumulator species and radish were not large enough to conclude that decreasing pH in the rhizosphere ofA. murale is a mechanism for heavy metal solubilization.Nickel concentrations inA. murale followed the typical pattern of an accumulator plant — more Ni was accumulated in the shoots than in the roots. Lower concentrations of Zn and Cd occurred in the shoots than in roots ofA. murale, and also of Ni in radish. The concentrations of Co inA. murale shoots were increased when Zn, Ni and Cd were absent from the nutrient solution. However, Co concentrations in radish shoots were independent of the concentrations of other heavy metals in the growth medium.