The aim of this study was to follow the gonadal development in freshwater crayfish Orconectes limosus (Rafinesque) by histological examination of ovaries and testes as well as monthly investigation of the gonadosomatic index over a period of one year. Male gonadosomatic index (IG) ranged between 0.11 to 0.79% with a minimum in July (0.11%) and maximum in September (0.79%) while in females it ranged between 0.25 to 6.15% with a minimum in July (0.25%) and maximum in April (6.15%). Between April and May, the histological dissection indicated presence of mature oocytes and oocytes undergoing resorption. Egg extrusion took place in mid April. During the summer months, the volume of oocytes gradually decreased. In winter and spring, the volume of oocytes began to increase during preparation for egg extrusion. The size of oocytes in the ovary increased from 0.2 mm at the beginning of the reproductive cycle to 1.8 mm immediately before egg extrusion. Average number of eggs in the ovary was 140.8 ± 51.63 (76-290). The ovary was of brown colour for the majority of the cycle, but white in June and July and orange in August and September. Mating started in October and continued through the winter. A difference was found in the proportions of testis and vas deferens in the male reproductive organ during the year. The male gonadosomatic index increased in September during preparation for mating (IG = 0.79%). During the mating season, the male spermatophores were predominantly filled with spermatozoa and sperm was also noted in the vas deferens. Two out of 15 males sampled during the winter were found to be intersex, in which atretic oogonia and oocytes were present at the periphery of testicular tissue and occupied less than 15% of testicular tissue. The evidence of intersex strongly suggested transitional stages of a gradual change of sex, which may be qualified as partial hermaphroditism.
After the occurrence of Austropotamobius torrentium in the Velika River in European Turkey, investigations to observe the distribution of crayfish species close to the Velika River have been carried out. The present observations showed that the distribution of A. torrentium expanded in European part of Turkey. In the summer of 2006, A. torrentium was found in the Madara Brook, but the abundance of A. torrentium in this brook was very low in comparison to the Velika River. Under the light of present observations, it could be concluded that besides the limited exploitation interest of A. torrentium in Turkey, this crayfish species increases its distribution in European Turkey, and more research should be carried out on its distribution and its either native or introduced presence in Turkey.
The ontogenetic changes in the diet of whitefish (Coregonus lavaretus) larvae were investigated during three consecutive years in a deep peri-alpine lake. Identification of the feeding habits of larvae in relation to their larval stage was performed using a PCA% in order to take into account the individual variability in larval diet. Although whitefish larvae are planktivorous, the present study points out ontogenetic changes in diet. While young larval stages are opportunistic feeders on small copepods, older stages feed preferentially on Daphnia sp.. Strong inter-annual variability has been observed in the dietary overlap between the successive larval stages. We show that the density and availability of the potential prey will affect the dynamics of the ontogenetic changes in the diet. Furthermore, it could probably alter the intra-specific competition between larval stages.
This paper concerns a study of some aspects of largemouth bass ecology in an Italian lake (Lake Bracciano). We assessed the success and possible impact of its recent introduction (1998) upon the fish community. From October 2001 to September 2002, 162 individuals were caught, measured, aged and submitted to biopsy (stomach and gonads were removed). Four age classes, from 0 + to 3 +, were observed in the population. Largemouth bass feeding activity was high in June, mostly eating fish (55.7%), crustaceans (in particular Palaemonetes antennarius, 37.5%), insects (4.5%) and molluscs (2.3%). The G.S.I. values showed an autumnal breeding period (from December to February) rather than the spring-summer one frequently described in North America. Moreover, bass attained sexual maturity during the second year of life (1+). These differences could be related to its recent introduction and the apparent success could represent a problem for other species in the Lake.
This laboratory study analyzes feeding preferences of a crayfish species with high invasive potentials, the red swamp crayfish Procambarus clarkii. We first conducted a series of multiple-choice tests among fresh plants (3 tests, one per each of three seasons, i.e. spring, summer, and autumn) and animals (1 test in summer). In the first tests, crayfish were simultaneously offered fresh pieces of seven plants of different growth forms and taxonomic groups, selected on the basis of their availability in the habitat. In the second test, the offered animals were dead earthworms, rainbow trout fry, and toad tadpoles. Then, a binary choice test was run in autumn between the most preferred plant (Urtica sp.) and earthworms. The percentages of organic C and N contents were measured for each food category using a gas-chromatography technique and the assimilation efficiency of both dry mass and organic content was assessed in a dedicated experiment. The results showed that P clarkii is selective when offered fresh plants, consuming a relatively larger biomass of Urtica (in the three seasons examined), green algae (in spring), and Polygonum (in summer and autumn). Surprisingly, crayfish did not exhibit preference for any animal prey. Also, P clarkii's feeding decisions seemed not to be associated with either the availability of plants in the habitat or their occurrence in the gut contents of wild crayfish. Neither did their ingested biomass depend on the organic content or assimilation efficiency. Procambarus clarkii preferred Urtica sp. over earthworms, notwithstanding the higher nutritional value and assimilation efficiency of the latter. The above results might suggest that feeding preferences of the species often depend on factors other than nutritional value and digestibility. Future studies will analyze all the possible factors together in order to unravel the rules that govern feeding preferences in crayfish. In the case of invasive species, such knowledge will highly contribute to planning science-based actions for their containment and mitigation.
A laboratory experiment was carried out to test the combined effects of ration size (1 vs 3% body weight, b.w.) and temperature (15 ± 2 vs 22 ± 2 °C) on moult increment and metabolic parameters of 80 juvenile noble crayfish (Astacus astacus). The maximum daily consumption (Cmax) and respiration rate (R) were used to calculate the growth scope (i.e. the difference between maximum daily energy consumption and energy costs at a given temperature). The conversion of R into a food-equivalent unit allowed the comparison with Cmax. Results showed that crayfish obtained the maximum moult increment when fed 3% b.w. while temperature seemed to play a less relevant role on growth rate per moult, affecting only the moulting frequency. Crayfish A. astacus fed ad libitum showed a relative insensitivity to the metabolic parameters (oxygen uptake, R and Cmax) within the analysed range of temperatures, possibly as a reflection of this “species” distribution across a broad variety of habitats with different thermal regimes. In the present study, A. astacus displayed characteristics proper of a K-selected species, as slow to moderate growth.
Specimens of the three known Greek crayfish species, Astacus astacus (Linnaeus, 1758), Astacus leptodactylus Eschscholtz, 1823 and Austropotamobius torrentium (Schrank, 1803), were collected from seven localities in Greece and were examined for the epibionts of Branchiobdella sp. (Annelida: Clitellata) and the aelosomatid Hystricosoma chappuisi Michaelsen, 1926 and the copepod Nitocrella divaricata (Chappuis, 1923). As a result, three branchiobdellid species, Branchiobdella parasita (Braun, 1805), Branchiobdella pentodonta Whitman, 1882 and Branchiobdella hexodonta Grüber, 1883 were found. This was also the first report of B. pentodonta from Greece as well as H. chappuisi, the latter being found on crayfish gills in one of the localities investigated. Moreover, the current work represents the first documentation of the presence of B. parasita and B. hexodonta in several localities in Greece.
Freshwater crayfish are found in 20 out of 53 Prefectures of Greece (38%) and they form isolated populations in relatively pristine water bodies. Three indigenous crayfish species (ICS) occur in Greek waters: Astacus astacus , Astacus leptodactylus and Austropotamobius torrentium , as well as one non-indigenous crayfish species (NICS) Pacifastacus leniusculus . Greece represents probably the most southern natural distribution limit for A. astacus and A. torrentium in the world. Concerning NICS, P. leniusculus was imported, at least in two cases, from Sweden and Germany during the early and late 1980’s respectively, in order to replace A. astacus stocks impoverished by human activities. Recently, Cherax quadricarinatus specimens have been seen in a restaurant’s aquarium and pet shop, raising fears about uncontrolled imports of alien pet species. During our 2004-2005 survey, we found that P. leniusculus established not only a thriving population in the artificial Lake Agra (Region of Central Macedonia), but also they co-occur with A. torrentium there. It is also suspected that A. astacus may co-occur there with these two species, as three large male specimens of A. astacus were caught in a creek close to the lake. Concerning A. leptodactylus , there are three sets of preserved samples from the River Evros (state border with Turkey in Thrace today), dated back to the 19th century, but no recent information about occurrence was available. But the accidental catch of six specimens of A. leptodactylus during May 2005 in that river re-documented the occurrence of the species. Finally, a deep-dwelling A. torrentium population with bluish legs was found to live in depths up to 7,800 meters inside the Aggitis Cave in northeastern Greece. There is a lot of work to be done on geographic distribution, population dynamics, genetics, reproduction, nutrition, diseases, and farming of crayfish species in Greece. Moreover, several actions should be undertaken to reform the existing legislation, in order to protect the native species and their habitats.
Cette étude réalisée en septembre 1996 dans le cadre du Projet d’Étude Participative AISA/IDESSA a permis de faire l’historique des activités halieutiques et la typologie de la pêche sur le lac Faé. La pêche dans ce réservoir est artisanale et de type individuel. Démarrée en 1980 avec l’implantation des pêcheurs étrangers originaires du Mali, cette activité est pratiquée par deux types d’acteurs : les professionnels (étrangers) et les occasionnels (Bakwés). Les engins de pêche sont ceux classiquement utilisés dans les pêcheries continentales de Côte d’Ivoire : filets maillants, mono et multifilaments, nasses (grillagées, en filets ou en bambou) et pièges en bambous de Chine. La densité des pêcheurs artisans sur le lac Faé est de 6,4 pêcheurs/km2, soit trois fois supérieure à la norme optimale de 2 pêcheurs/km2 admise par la législation ivoirienne Par conséquent, des mesures de gestion devraient être prises par la Direction de la Production Halieutique (DPH) pour contrôler le flux migratoire des pêcheurs vers cette retenue, afin d’infléchir la densité observée. Le maintien ou l’accroissement de celle-ci pourrait engendrer une surexploitation rapide des stocks, et constituer une source potentielle de conflits entre étrangers et autochtones. A cet effet, des recommandations pour une pratique durable de la pêche sur cette retenue sont proposées.
The narrow-clawed crayfish Astacus leptodactylus Eschscholtz, 1823, is widely distributed in eastern European and western Asian countries. However, species presence in Greece was documented only by limited museum conserved specimens dating back to 1893. Recently (May 2005) several crayfish were captured in the Evros River (close to city of Didimotiho) and these were identified as A. leptodactylus . The present work confirms the presence of A. leptodactylus in the Evros River still hundred and twelve years later and introduces the possibility of A. leptodactylus being indigenous to Greece.
L’évaluation de la survie du saumon Atlantique entre la ponte et l’émergence des alevins hors des graviers est réalisée dans le bassin de la Nivelle dans les domaines accessible (trois tronçons) et non accessible (trois tronçons) aux géniteurs. Pour ce faire, des capsules d’incubation de 12 cm3, contenant des œufs fraîchement fécondés, sont insérées dans des frayères artificielles et naturelles. Le débit et la température de l’eau de surface, l’oxygène dissous des eaux de surface et interstitielle et les caractéristiques granulométriques du substrat des frayères sont contrôlés pendant toute la durée de l’expérience. La survie, de 28,6 % en moyenne dans l’ensemble des sites, est plus élevée dans les tronçons de l’amont (52,7 % dans la Très Haute Nivelle et son affluent, le Lapitxuri) que dans les autres sites, dont ceux actuellement colonisés par l’espèce (21,5 %). Il n’est pas observé de différence de survie entre les frayères artificielles et naturelles. Les mortalités interviennent essentiellement lors des épisodes de crues avant l’éclosion. Une corrélation positive forte existe entre la saturation en oxygène de l’eau interstitielle et la survie. Pour une saturation minimum en oxygène au-dessous de 62 %, la survie reste inférieure à 27 %. En revanche, la composition granulométrique du substrat ne semble pas agir directement sur la survie. Ce facteur n’étant pas corrélé avec l’oxygène dissous, ceci suggère que dans ce cours d’eau, le flux circulant dans les frayères ne provient pas uniquement de l’eau de surface, mais aussi de la nappe alluviale pauvre en oxygène dissous.
Le blanchiment des œufs non fécondés dans les pontes de salmonidés en incubation artificielle permet leur élimination par tri mécanique. Le déclenchement de ce phénomène normalement plus ou moins tardif durant l’incubation a pu être accéléré grâce à une brève exposition des œufs à une solution de sel de mer. Les modalités et les effets de cette exposition sur les taux de mortalité et de malformations des embryons ont été testés sur des pontes de truite arc-en-ciel à divers stades de développement (140, 190 et 240 degrés*jours). Le passage durant 1 à 20 min dans une solution saline de 30 à 120 g/l a permis d’augmenter significativement le taux de blanchiment des œufs non fécondés sans affecter celui des œufs fécondés. Toutefois, par un effet mécanique, la manipulation nécessaire au traitement a entraîné une augmentation significative de la mortalité embryonnaire pour une manipulation à 140 degrés*jours et du taux de malformations larvaires pour une manipulation à 190 degrés*jours. A 240 degrés*jours, la manipulation n’a pas affecté le développement embryonnaire mais a entraîné un retard de l’éclosion de quelques heures. Cette étude offre de nouvelles perspectives pour améliorer le tri mécanique des œufs fécondés et non fécondés au cours de l’incubation chez la truite arc-en-ciel.
The chemical composition of natural food sources (periphyton, suspended solids and sediment) and gut content of Oreochromis niloticus in two extensive aquaculture reservoirs from a rural area (Gueyo, southwest of Ivory Coast) were determined in order to assess the quality of the natural food ingested.The percentage of the chemical components in the three food sources in the two sites show an important part of hydrolysable organic matter in the periphyton (65 and 67%), even though the mineral matter represents more than half of the total dry weight of suspended solids (59 and 63%) and sediment (76 and 63%). In the two sites, fibers represent less than 15% of these three resources. Protein contents (19%) and Proteins/Energy ratio (17 mg.kJ(-1)) in periphyton are respectively 2 and 3 times above the values measured for the two other resources.The biochemical analysis of the gut contents shows that proteins are in low percentage in the food ingested by O. niloticus (7 and 11 % in the two sites). On the other hand, the percentages of fibers (12 and 16%) and lipids (11 and 8%) as well as the Proteins/Energy ratios (6 and 12 mg.kJ(-1)) seem to meet the growth requirements of the studied species. The average weights of the fishes at the end of the farming cycle are indicative of the ability of O. niloticus to grow on a poor food context characterized by low nitrogen compounds, as long as a low density is applied in the aquaculture sites.
Studies on feeding periods, daily ration and relative artificial and natural food consumption in populations of juveniles (6 g), sub-adult (30 g) and adults (250 g) of Oreochromis niloticus were realized. Sampling took place over two 24-hour cycles in four concrete basins (juvenile) and eight ponds (sub-adult and adult). Fish were caught at three hourly intervals. Stomach contents of different populations were microscopically analysed. The gut content weights were submitted to the feeding model MAXIMS to determine the ingestion, evacuation rates and daily ration. Two peak feeding periods were evident. The fish showed diurnal diel feeding periodicity. Outside the food distribution periods (9 h and 15 h), the gut contents were mostly composed of natural food in juvenile and sub-adult populations. In addition, in adult population, artificial food was more important from 9 h to 24 h. outside this period, the gut content in each fish population was only constituted of natural food. The daily rations were about 10 %, 6.7 % and 3.7 % respectively for the juvenile, sub-adult and the adult. In that order, the consumed natural food represented 4 % 2.3 % and 1 %. Respective values of the artificial food estimated were 6 %, 4.45 and 2.7 % for the juvenile, sub-adult and the adults.
A recent PCR-test developed for identification of Aphanomyces astaci, the organism responsible for crayfish plague, provided false positives for Aphanomyces frigidophilus, Aphanomyces repetans, and some Saprolegnia spp. Real-time PCR showed that with the designed primers, A. astaci and A. frigidophilus cannot be distinguished. The results of this study show that this particular crayfish plague PCR-test ought to be improved and that molecular-based techniques need to be contrasted to histological evidences and disease history.
The abundance of European perch in Lake Piediluco has significantly dwindled in the last few years. The present study on diet overlap between perch and ruffe was prompted by the rapid expansion of the ruffe stock in the lake. This species was first found in the lake in 1996 and has since become one of the most abundant. The degree of diet overlap between the two species was analyzed by using data on the stomach contents of 275 European perch and 328 ruffe. Results are expressed as abundance (%N), occurrence (%S), weight percentage (%W) and index of predominance (Ip). The diet overlap index (α) was calculated by means of Schoener’s formula using the %W of each food item. As an estimate of the diet width of both species, we used Levins’ indexes of niche breadth (B) and standardized measurement of niche breadth (BA). Both species are strictly carnivorous, feeding mainly on invertebrates: the most important diet components were dipterans and crustaceans, but the European perch also feeds on fish. In the perch, the Levins index was greater (B=4.332) than that calculated for the ruffe (B=2.262). During the ontogenesis of the European perch, there is a rather pronounced diet shift: dipterans form the largest portion of the diet at all ages, though in older perch fish-eating becomes increasingly evident. Benthic crustaceans tend to be consumed in greater quantities by the 3+ age-class, though they are also found in the stomachs of specimens of all ages. Ruffe, by contrast, do not display a pronounced ontogenetic diet shift. The index of diet overlap between the two species was rather high, the maximum α value being 0.853; values indicate a high degree of diet overlap in the younger ageclasses (1+, 2+ and 3+), with a greater differentiation between the diets of the two species emerging as the age of the perch increased. Our research also clarified some of the biological characteristics of the European perch in Lake Piediluco, namely, theoretical growth in length, weight at length and relative weight. These analyses enabled us to compare the growth characteristics of the European perch during periods when ruffe stocks differed in terms of abundance. All of the results indicate that the growth conditions of the European perch population in Lake Piediluco are steadily worsening. This provides indirect confirmation of a negative interaction with the ruffe.
Since the end of the XIXth century, the distribution of crayfish in France has gone through deep changes, and the introduction of allochtonous crayfish, essentially from the North American continent, has forever changed the French and European crayfish landscape. The four surveys organised in France by the Conseil superieur de la peche since 1977 allow following the evolution of the different species of crayfish present on the national territory, showing each time the large expansion of the exotic species and the recess of the native species. The 2006 survey shows the same tendency and the situation of our three native species must now be considered as alarming. Two of these species, Austropotamobius torrentium and Astacus astacus, are close to extinction, and the third one, Austropotamobius pallipes, can now be found on the upmost parts of the watersheds, confined in areas where the first signs of climatic changes can be seen, and under the pressure of the exotic species which are still making their way further up. Pacifastacus leniusculus and Procamabrus clarkii are showing the strongest geographical expansion during the 2001-2006 period. Everywhere they appear to be very strong competitors, more aggressive, resistant to pathologies, able to colonize varied environments. They are indeed colonizing new departments, new watersheds, and thus eliminating native species.
Genetic studies on the populations of Austropotamobius pallipes complex from Alessandria province (N-Italy), conducted on the basis of variations recorded in the sequences of mitochondrial DNA in the gene 16S RNA, have allowed to single out an overlapping zone of the distribution areas of the two taxa pallipes and italicus. In the crayfishes from a creek where both species have been ascertained to be present, the authors have applied the same molecular marker in order to investigate the distribution of the two taxa, stressing the syntopy of A. pallipes and A. italicus. Multivariate statistical techniques on 21 morphological parameters have been used in order to single out possible distinctive features of 31 crayfishes collected in this site, and of 225 crayfishes obtained from four sites in neighbouring areas. The results confirm the presence of a high morphological variability, not only at interspecific, but also at intraspecific level, which does not allow to distinguish the two species on the basis of the features measured in the present study.
Antioxidant parameters, such as total glutathione, glutathione S-transferase, glutathione peroxidase, glutathione reductase, glyoxalases, catalase, and some heavy metals such as, lead, cadmium and chromium were examined in hepatopancreas of both sexes of Procambarus clarkii collected seasonally from Lake Trasimeno, from winter 20002003 to autumn 2003. Heavy metals content in hepatopancreas in males and females of P clarkii was low and did not vary through the sampling periods and between sexes. On the contrary, crayfish exhibited sex-dependent differences in levels of some enzyme activities and of total glutathione, and no apparent relationship was found between contaminant burdens and antioxidant indexes in hepatopancreas. Because measured metal concentrations were low, other factors, presumably, were involved in antioxidant variations in P clarkii and these latter seemed to be affected more by biological and environmental factors, other than those related to pollutants body burdens.
La population d’écrevisses signal arrivées en 1976 dans le Léman continue son expansion le long de la zone littorale à l’ouest de Thonon-les-Bains. En 2001, la population s’étendait jusqu’à Séchex avec une forte densité (82 indiv./nasse) de Thonon à Anthy. En 2005, les écrevisses se rencontrent jusqu’à Yvoire, avec une densité maximum à Excenevex (78 indiv./nasse). Le long de la zone littorale, la vitesse de colonisation est de 500-1 000 m/ an. Du fait, d’une part, de leur croissance rapide dans les milieux nouvellement colonisés et, d’autre part, de la pression exercée par la pêche professionnelle dans les milieux anciennement colonisés, la taille moyenne des individus exploitables augmente de la région d’origine jusqu’à proximité du front de colonisation, comme cela a été mis en évidence en 2004 entre Thonon (89,5 mm) et Excenevex (108,3 mm). L’effet de la pêche sur la réduction de la taille des écrevisses est important : à Sciez, avec l’arrêt de la pêche dès la fin 2004, la taille moyenne est passée de 105,1 à 108,5 mm entre 2004 et 2005. L’impact des écrevisses sur le milieu est discuté, notamment sur les herbiers à macrophytes et sur les limnées vecteurs de la forme larvaire de Trichobilharzia sp., entraînant une forte diminution des cas de dermatite du baigneur dans les zones colonisées par les écrevisses.
