1,720,967 research outputs found
EVALUATION OF THE AMERICAN WATERWEED (ELODEA CANADENSIS MICHX.) AS SUPPLEMENTAL FOOD FOR THE NOBLE CRAYFISH, ASTACUS ASTACUS
No full textWe conducted a preliminary study to evaluate the capacity of summerling Astacus astacus to consume the American waterweed (Elodea canadensis Michx.).under artificial rearing conditions. Summerling A. astacus (initial b.w.: 0.32 ± 0.02 g) were cultured (50 crayfish/m2) in 600l tanks for 89 days. The experimental design was composed of three treatments as follows: control diet (D) (crude protein: 40.9% DM; ether extract: 7.4% DM), elodea (E) (crude protein: 25.8% DM; ether extract: 1.4% DM) and control diet + elodea (D + E) with three replicates per treatment. Temperature, dissolved oxygen, and other water parameters were measured weekly (T: 20.1°C; O2: 7.2 mg/l; pH: 7.5; N-NH4: 0.05 mg/l; N-NO2: 0.01 mg/l; N-NO3: 29.9 mg/l). The relative growth rate was significantly (P < 0.01) higher in treatment D + E (195%) and D (143%) than in E (65%). The reduced growth observed in crayfish fed elodea only can probably be due to the lower dietary lipid level of the plant respect to the standard crayfish requirements. At the end of the experiment, the survival rate of A. astacus was higher (P < 0.05) for the treatment D + E (87%) and D (81%), compared to E (56%). Our results suggest that E. canadensis can be used as a non-expensive supplemental food in order to increase growth and survival in summerling noble crayfish. They also showed that A. astacus has the potential to consume this macrophyte in nature
Effects of diet and temperature on growth of juvenile noble crayfish, Astacus astacus
No full textA 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
Effects of ration size and temperature on growth and metabolic parameters of juvenile noble crayfish Astacus astacus L.
No full textA 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 growth and metabolic parameters of 80 juvenile noble crayfish (Astacus astacus
L.). The maximum daily consumption (C, g·g-1) and respiration rate (R, g O2·g-1·d-1) 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 C and R into a food-equivalent unit (g food·g-1·d-1) allowed their comparison. Results
showed that crayfish grew faster when fed 3% b.w. while temperature seemed to play a less relevant role on growth
variables, affecting the moulting frequency only. Crayfish A. astacus fed ad libitum showed a relative insensitivity
of the metabolic parameters (oxygen uptake, R and C) within the analysed range of temperatures, possibly
reflecting its distribution across a broad variety of habitats with different thermal regimes. In the present study,
A. astacus displayed some characteristics specific of a K-selected species, such as slow to moderate growth and low
juvenile survival rate
Nonrandom mating, mate choice, and male-male competition in the crayfish Austropotamobius italicus, a threatened species
No full textUnder the rationale that behavioral studies may contribute to the conservation of threatened species, we analyzed mating behavior of the crayfish Austropotamobius italicus in the laboratory. Our objectives were to investigate whether nonrandom mating by size occurs in this species and to explore the role exerted by mate choice and male-male competition in inducing mating. We observed 17 "quartets" (one female and three differently sized males), divided into three groups based on the female size. To understand the influence of male-male competition on mating, we compared six quartets with six "duets" (one female and one male). Our results clearly show that mating in A. italicus is nonrandom caused by the clear mating advantage of larger males. In fact, as compared to smaller size categories, large males paired more often and for a longer time, and interrupted the final phase of mating less frequently. Male size-advantage mostly derives from an active female choice for large partners, combined with dominance of big males in intrasexual competition. However, a restricted mating period and the low number of receptive females may make males relatively indiscriminate in their overt behavior towards females. Female selection of big males and male-male competition over mates, also in the form of sperm competition, should result in a skewed reproductive success among males. As a consequence, populations with few big males would be characterized by a low heterozigosity and therefore by little genetic variation upon which selection acts. Our results should warn managers to pay more attention to the size structure of crayfish populations that are used for reintroductions
Conserving indigenous crayfish: stock assessment and habitat requirements in the threatened Austropotamobius italicus
No full text
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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