The aim of this study was to compare survival and growth of juvenile narrow-clawed crayfish (Astacus leptodactylus) and signal crayfish (Pacifastacus leniusculus) fed only with experimental pellets (45% of proteins, 6% of fat, 20% crude fibre) under controlled conditions. The animals were reared in 12 (50 l) circular plastic tanks, the narrow-clawed crayfish set-ups being designated A1 and A2, the signal crayfish set-ups P1 and P2. The initial stocking densities for each species were 600 (A1, P1) and 1,200 (A2, P2) juveniles stage 2 per square metre for each set-up in three replicates. The experiment lasted 92 days under continuous photoperiod (L:D 24:0; 100 LUX) conditions at a temperature of 22.0 ± 0.1°C and an oxygen saturation > 90%. One shelter (plastic tube) was provided for 2 crayfish in each set-up.The highest survival rate was obtained for signal crayfish from set-up P1 (47.5%), the lowest for narrow-clawed crayfish from set-up A2 (22.8%). Crayfish survival evidently depends on the stocking density: in set-ups A1 and P1 it was about 16% higher than in set-ups A2 and P2 (P < 0.05). Mortality was significantly higher (P < 0.05) in both species during the first 30 days of the experiment (48-77% of the total mortality) than during the subsequent two months of the experiment (< 20% of the total mortality).The final body size was the largest in narrow-clawed crayfish from set-up A1 (799 mg, 29.2 mm) and the smallest in signal crayfish from set-up P2 (534 mg, 26.5 mm). Specimens of narrow-clawed crayfish were larger than signal crayfish, and the specimens of both species in set-ups A1 and P1 were larger than those in set-ups A2 and P2. During the first 30 days of the experiment the specific growth rate (SGR) of both species in all set-ups was twice the value reported during the subsequent two months (P < 0.05). La survie des écrevisses dépend évidemment de la densité de départ: dans les lots A1 et P1, la survie est supérieure de 16 % par rapport à celle des lots A2 et P2 (P < 0,05). La mortalité a été significativement plus importante (P < 0,05) pendant les 30 premiers jours de l'expérience (48-77 % de la mortalité totale) que pendant les deux derniers mois (< 20 % de la mortalité totale). Key-words:Les écrevisses à pattes grêles du lot A1 ont présenté les tailles corporelles les plus grandes (799 mg ; 29,2 mm) alors que les plus petites ont été enregistrées dans le lot P2 (534 mg ; 26,5 mm). D'une façon générale, les écrevisses à pattes grêles étaient plus grandes que les écrevisses signal et les individus des lots A1 et P1 étaient aussi plus grands que ceux des lots A2 et P2. Pendant les 30 premiers jours de l'expérience, le taux de croissance spécifique (SGR) de chaque espèce (A1, A2, P1, P2) était plus important que celui mesuré dans les deux mois suivants (P < 0,05).

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Fourteen easily recognizable stages of embryonic, larval and juvenile development are described in order to provide a model for early ontogeny in bream (Abramis brama L.). The proposed developmental stages are applicable both in labo ratory studies and in field work, enabling quantitative description of the course and rate of bream early ontogeny and give the possibility to use statistical analysis (i.e. comparison of mean length-at-developmental stage). Early development of bream was studied in a wide range of rearing temperatures (13.5-34.0 0c) and food supply (four food regimes), the two most important environmental factors influencing fi sh survival and development. In the lowest and highest test temperatures, the same stage was ob served in fish of significantly smaller size. Fish reared under different feeding regi mes differed in size when they reached particular developmental stages. Generally, fish kept in disadvantageous conditions (i.e. semi-lethal temperature, poor quality of food) attained the successive developmental stages at smaller size.

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Acta Technologica Agriculturae 1/2016Dušan Páleš et al.The most effective way for determination of curves for practical use is to use a set of control points. These control points can be accompanied by other restriction for the curve, for example boundary conditions or conditions for curve continuity (Sederberg, 2012). When a smooth curve runs only through some control points, we refer to curve approximation. The B-spline curve is one of such approximation curves and is addressed in this contribution. A special case of the B-spline curve is the Bézier curve Rédl et al., 2014). The B-spline curve is applied to a set of control points in a space, which were obtained by measurement of real vehicle movement on a slope (Rédl, 2007(Rédl, , 2008. Data were processed into the resulting trajectory (Rédl, 2012;Rédl and Kučera, 2008). Except for this, the movement of the vehicle was simulated using motion equations (Rédl, 2003;Rédl and Kročko, 2007). B-spline basis functionsBézier basis functions known as Bernstein polynomials are used in a formula as a weighting function for parametric representation of the curve (Shene, 2014). B-spline basis functions are applied similarly, although they are more complicated. They have two different properties in comparison with Bézier basis functions and these are: 1) solitary curve is divided by knots, 2) basis functions are not nonzero on the whole area. Every B-spline basis function is nonzero only on several neighbouring subintervals and thereby it is changed only locally, so the change of one control point influences only the near region around it and not the whole curve.These numbers are called knots, the set U is called the knot vector, and the half-opened interval 〈u i , u i + 1 ) is the i-th knot span. Seeing that knots u i may be equal, some knot spans may not exist, thus they are zero. If the knot u i appears p times, hence u i = u i + 1 = ... = u i + p -1 , where p >1, u i is a multiple knot of multiplicity p, written as u i (p). If u i is only a solitary knot, it is also called a simple knot. If the knots are equally spaced, i.e. (u i + 1 -u i ) = constant, for every 0 ≤ i ≤ (m -1), the knot vector or knot sequence is said uniform, otherwise it is non-uniform.Knots can be considered as division points that subdivide the interval 〈u 0 , u m 〉 into knot spans. All B-spline basis functions are supposed to have their domain on 〈u 0 , u m 〉. We will use u 0 = 0 and u m = 1.To define B-spline basis functions, we need one more parameter k, which gives the degree of these basis functions. Recursive formula is defined as follows:This definition is usually referred to as the Cox-de Boor recursion formula. If the degree is zero, i.e. k = 0, these basis functions are all step functions that follows from Eq. (1). N i, 0 (u) = 1 is only in the i-th knot span 〈u i , u i + 1 ). For example, if we have four knots u 0 = 0, u 1 = 1, u 2 = 2 and u 3 = 3, knot spans 0, 1 and 2 are 〈0, 1), 〈1, 2) and 〈2, 3), and the basis functions of degree 0 are N 0, 0 (u) = 1 on interval 〈0, 1) Acta In this co...

High content of humic substances and low pH values are factors limiting the species richness and abundance of some organisms in dystrophic lakes. Unfavourable winter conditions (i.e. low water temperature, poor light conditions, ice/snow cover) may additionally restrict their development. The aim of this study was to compare ice-on (winter) and ice-off (summer) abiotic (organic carbon, total phosphorus and nitrogen) and biotic (chlorophyll a, phytoplankton, ciliates, rotifers, crustaceans, fish) parameters in five dystrophic lakes of the Wigry National Park (north-east Poland). We tested the hypothesis that the abundance and diversity of planktonic organisms in dystrophic lakes could be lower in winter than in summer. Our results showed that the winter period, with ice and snow cover, was characterised by clearly higher oxygen concentrations, pH values and conductivity, but lower total phosphorus concentrations, species richness of phytoplankton, ciliates, rotifers and crustaceans, and phytoplankton to zooplankton biomass ratios in comparison to the summer. All of the studied groups of organisms, except rotifers, reached relatively high abundances and biomasses in both seasons and, in some lakes, they were higher in winter than in summer. Our results suggest that fish composition and abundance did not play an important role in structuring plankton communities. The small dystrophic lakes, although located close to one another, differed in terms of abiotic parameters and had specific species compositions of phyto-and zooplankton. Warmer winters, which are the result of climate change, may favour the intensive development of planktonic communities under the ice in dystrophic lakes of temperate climatic zones.

Interaction between juvenile narrow-claw crayfish, Astacus leptodactylus (Eschscholtz), and common water frog, Rana esculenta (L.), tadpoles or common blue damselfly, Enallagma cyathigerum (Charpentier), larvae during rearing under controlled conditions Dariusz Ulikowski, Iwona Piotrowska, £ucjan Chybowski, Tadeusz Krzywosz, Piotr Traczuk Received -07 July 2014/Accepted -06 October 2014. Published online: 31 December 2014 ©Inland Fisheries Institute in Olsztyn, Poland Citation: Ulikowski D., Piotrowska I., Chybowski £., Krzywosz T., Traczuk P. 2014 -Interaction between juvenile narrow-claw crayfish, Astacus leptodactylus (Eschscholtz), and common water frog, Rana esculenta (L.), tadpoles or common blue damselfly, Enallagma cyathigerum (Charpentier), larvae during rearing under controlled conditions -Arch. Pol. Fish. 22: 257-264.Abstract. Interactions were studied among juvenile narrow-claw crayfish, Astacus leptodactylus (Eschscholtz), and common water frog, Rana esculenta (L.), tadpoles and common blue damselfly, Enallagma cyathigerum (Charpentier), larvae during rearing under controlled conditions. Interactions among the species studied had a positive impact on the survival of the crayfish, but the differences were not statistically significant (P ³ 0.5). The juvenile crayfish attacked and consumed the frog tadpoles and damselflies, but the juvenile crayfish very rarely fell prey to them. Only in the initial stage of life and during molting did larval damselflies prey upon juvenile crayfish. After 30 days of the experiment the interaction between crayfish-tadpoles and crayfish-larval damselflies was not noted to have had a statistically significant (P ³ 0.05) impact on crayfish growth. Juvenile crayfish aggression toward tadpoles and larval damselflies was often offset by the loss of even both chelipeds. In the crayfish-larval damselfly interaction the loss of both chelipeds was three-fold more common than it was in the crayfish-tadpole interaction; however, these differences were not statistically significant (P ³ 0.5). The effect of intraspecific interaction (crayfish-crayfish) was more a threat in terms of mortality from cannibalism than were interspecific interactions (crayfish-tadpole and crayfish-larval damselfly).

A procedure is proposed to assess the impact of various relationships found in the literature and is used to convert acoustic target strengths (TS) to fishes’ total length (TL) with respect to the compatibility of fish length data obtained from vertical hydroacoustics and gillnets. The study used one set of data collected with a 120 kHz echosounder across the mesotrophic, dimictic Lake Dejguny. Four general multi-species TS–TL relationships were tested for the maximum dorsoventral characteristic: (1) a relationship developed using mainly West Atlantic marine and brackish water fish for various frequencies, (2) a relationship developed using fish from the Salmonidae, Percidae, and Cyprinidae families at 120 kHz, as well as the relationship shown by two generalized equations for representatives of (3) the Cyprinidae family (200 kHz) and (4) the Percidae family (200 kHz). In addition, two other equations were developed for (5) perch (Perca fluviatilis) and (6) roach (Rutilus rutilus). The procedure for selecting the most appropriate TS–TL ratio began by determining the TS threshold that would eliminate small fish that were ineffectively caught with gillnets. Depending on the TS–TL relation, the threshold ranged from −48.5 dB to −45.5 dB, and the corresponding TL was in the range of 62.3–93.0 mm. Then, using linear regression, the relationship between the percentage of caught fish organized in length classes (TL), whose boundaries were determined using the tested TS–TL relationships, and the share of fish recorded acoustically in the corresponding TS classes (with a 1.5 dB interval) was examined. The fit of the regression model to the data (percentage) was assessed using the coefficient of determination r2, the mean absolute error (MAE), the Nash–Sutcliffe model efficiency coefficient (NSE), and root mean square error (RMSE). For the data from Lake Dejguny, the most similar distribution of fish echo proportions and the corresponding distribution of total length (TL) for fish larger than 62 mm were obtained using the TS–TL relation developed using fish from the Salmonidae, Percidae, and Cyprinidae families (2), and for fish larger than 74 mm, the relation was developed for the family Pericidae (4). No evidence was found to unambiguously verify the meanings of different sound frequencies (120 and 200 kHz) for which the TS–TL relationships used in the analysis were derived. The proposed procedure can be used to select the optimal regression equation.