Samples of invasive cyprinid fish, the Prussian carp (Carassius gibelio), were collected by fyke nets in Leszczynskie Lakeland (Poland) during the summer and autumn, 2010, and during the spring, 2011. All captured fish were females. For each fish, the total weight (W,g) and the standard length (L,cm) were measured and Fulton’s condition factor(KC=100 W/L3)was computed. Graphical investigation and the Mann-Whitney-Wilcoxon test showed statistically significant location shift of theKCdistribution from summer to autumn (upward) and from autumn to spring (downward). Relationship between total weight and standard length was described with the mean growth curveE(W∣L)=aLb. Seasonal parameters (aandb) were estimated with a nonlinear regression approach, that is, numerical optimization methods. Growth was allometric in summer and autumn and isometric in spring. The differences between summer and autumn growth curves and between autumn and spring growth curves were statistically significant. The seasonality exhibited by the condition factor and the growth curve may be due to different spawning, breeding, and feeding activity in the different seasons and to variable environmental conditions.
Age, growth and reproductive characteristics of six westslope cutthroat trout Oncorhynchus clarkii lewisi populations were studied in the south-western Rocky Mountains in Alberta, Canada. Sagittal otoliths were collected from 605 fish ranging in size from 36 to 250 mm (fork length). The maximum detected age (13 years for females and 12 for males) was higher than has been reported previously in published literature; but no significant differences in age distributions between males and females were found. Length growth rates, estimated using the von Bertalanffy growth function, showed that males and females had similar growth rates. Sex ratios varied between 0.3 to 2.0 females per male. Age and size at 50% maturity were greater for females than males (4.9 years and 139 mm v. 3.7 years and 125 mm). Mature females were yearly spawners with highly variable fecundities (mean ± S.D. = 223 ± 94) and their ovaries contained both developed and undeveloped eggs. Across all populations, mean instantaneous mortality rate (Z) was estimated as 0.555, annual survival rates for 0-1 year-old fish were 3.2 and 57.4% for older fish. An altitudinal distribution gradient was observed, with older fish occupying upper stream reaches. This study provides a comprehensive evaluation of biological characteristics and structure of O. c. lewisi populations inhabiting small, mountain streams and should provide useful basic information for management policies of this threatened species in eastern drainage of the Canadian Rocky Mountains.
The results of an analysis of the autumn diet of the Chinese mitten crab, Eriocheir sinensis, are presented and the crab's effects on the most common species of the flora and fauna of the River Odra estuary are assessed. Examination of crab gut contents showed the diet to be composed of detritus (59.6%), vascular plants (10.7%), and animals, mainly copepods and chironomid larvae (10.4%). The crabs, kept for 2 months in tanks under abiotic and biotic conditions similar to those prevailing in the Odra estuary, diminished the biomass of aquatic plants (particularly that of Elodea canadensis) by almost 12%, and that of aquatic macroinvertebrates (26% reduction of chironomid biomass and more than 21% reduction of tubificid biomass), which, at a high abundance of the crab, may have an adverse effect on the composition of species of plants and animals in the estuary. RÉSUMÉLes résultats des analyses du régime alimentaire d'automne du crabe chinois, Eriocheir sinensis, sont présentés, et les effets de ce crabe sur les espèces les plus communes de la flore et de la faune dans l'estuaire de la rivière Odra (Pologne) sont évalués. L'étude des contenus stomacaux du crabe montrent que le régime alimentaire est composé de détritus (59,6%), de plantes vasculaires (10,7%), et d'animaux, essentiellement copépodes et larves de chironomes (10,4%). Les crabes maintenus pendant 2 mois en aquariums sous des conditions abiotiques et biotiques similaires à celles existant dans l'estuaire de l'Odra, diminuent la biomasse de plantes aquatiques (particulièrement celle d' Elodea canadensis) d'au moins 12% et celle des macroinvertébrés aquatiques (26% de réduction de chironomidés et plus de 21% de réduction des tubificidés), ce qui, avec une forte abondance de crabes, pourrait avoir des effets adverses sur la composition spécifique des plantes et des animaux dans l'estuaire.
Abstract:The aim of the study was to analyze and assess the possibility of using a two-stage fi ltration system with ceramic membranes: a 3-tube module with 1.0 kDa cut-off (1 st stage) and a one-tube module with 0.45 kDa cut-off (2 nd stage) for treating effl uent water from a juvenile African catfi sh aquaculture. The study revealed that during the 1 st fi ltration stage of the effl uent water, the highest degrees of retention were obtained with respect to: suspended solids SS (rejection coeffi cient R I =100%), turbidity (R I =99.40%), total iron (R I =89.20%), BOD 5 (R I =76.0%), nitrite nitrogen (R I =62.30%), and COD Cr (R I =41.74%). The 2 nd fi ltration stage resulted in a lower reduction degree of the tested indicators in comparison to the 1 st fi ltration stage. At the 2 nd stage, the highest values of the rejection coeffi cient were noted in for the total iron content (R IV =100%), COD Cr (R IV =59.52%; R V =64.28%, R VI =63.49%) and turbidity (R IV and R V = 45.0%, R VI =50.0%). The obtained results indicate that ceramic membranes (with 1.0 and 0.45 kDa cut-offs) may be used in recirculation aquaculture systems as one of the stages of effl uent water treatment.
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