Feeding strategies and resource utilization of 0+ perch, Perca fluviatilis L., in littoral zones of shallow lakes
The aim of the study was to analyze the diet and feeding strategies of 0+ perch, Perca fluviatilis L., in two lakes (Gosławskie and Dołgie Wielkie) with different trophic and thermal regimes. Water temperature was higher in Lake Gosławskie (Mann-Whitney test, P<0.01), but oxygen concentration was similar in both lakes (Mann-Whitney U test, P<0.05). The mean abundance, biomass, and species richness of zooplankton during the study period were statistically significantly lower in Lake Gosławskie (test U Mann-Whitney, P < 0.0001. The share of perch with empty digestive tracts was very low. The fish from Lake Dołgie Wielkie had higher condition factors (mean 1.87) than did those from Lake Gosławskie (1.73). The analysis of the size structure of the prey consumed by perch from the two lakes indicated that the fish employed different foraging strategies. In Lake Dołgie Wielkie the perch consumed a large quantity of small plankton organisms (copepodites and Daphnidae) that occurred in large quantities, while in Lake Gosławskie, where zooplankton abundance was low, the basic diet comprised larger organisms (Sida crystallina, larval Chironomidae). Perch feeding intensity in Lake Dołgie Wielkie was positively correlated with body length, while in Lake Gosławskie it remained at the same level.
Management of fish populations in lobelia lakes in the vicinity of Bytów (northern Poland)
The aim of the studies was to describe the fisheries management of five lobelia lakes and one non-lobelia reference lake. Data from commercial catches was used to estimate the size of the catches, and to determine the species and ecologial structure of the catches, and to describe stocking. During the period from 1968 to 2006, eleven fish species belonging to five families were noted in the catches. The species structure of the commercial catches of the analyzed lobelia lakes corresponded to that of either vendace or eutrophic lakes. Catches made in lobelia lakes were from 2.5 to 5-fold smaller in comparison to the reference lake. The dominant species in commercial catches made in basins with lobelia vegetation were roach, Rutilus rutilus (L.), and pike, Esox lucius L., but bream, Abramis brama (L.), vendace, Coregonus albula (L.), and carp, Cyprinus carpio L., also occurred in some lakes. Pike was caught most frequently, followed by bream, roach, and perch. The largest catches were made in either March or November. During the period from 1968 to 2006, the lakes were stocked with ten fish species, nine of which were noted in the official statistics. Only six species occurred naturally in these lakes. Peled, Coregonus peled (Gmelin), is an alien species, and its occurrence was certainly connected with stocking. Pikeperch, Sander lucioperca (L.), was translocated outside of its area of natural occurrence, while carp and Prussian carp, Carassius gibelio (Bloch), were alien species.
The Significance of Stone Moroko, Pseudorasbora Parva (Temminck and Schlegel), in the Small-Sized Fish Assemblages in the Littoral Zone of the Heated Lake Licheńskie
The aim of the study was to determine changes in the seasonal abundance of stone moroko, Pseudorasbora parva (Temminck and Schlegel), and to identify the role this alien species plays in the littoral zone of a heated lake. This study also aimed at defining the habitat preferences of this species and describing the relations between the relative abundance of stone moroko and the occurrence of submerged vegetation. A significant dependence was determined of the degree to which the lake bottom is covered with macrophytes and the occurrence of stone moroko. The fish caught belonged to 14 species and 2 families. Stone moroko preferred habitats that were abundantly overgrown with submerged vegetation and avoided areas devoid of macrophytes. Thus, as the bottom cover increased, so did the relative number of this fish. In light of habitat availability and its food preferences, the abundant occurrence of this species poses a serious threat to the endemic ichthyofauna.
The aim of this paper is to present the results of studies on the phenology of the spawning of fish in two lakes with different degrees of heated waters. The studies performed indicated that heating the waters distinctly hastened fish spawning in comparison to the same species of fish inhabiting waters with normal thermal conditions. Spawning usually occurred two to three weeks earlier in the heated Lake Licheńskie than it did in Lake Ślesińskie, which has waters with a natural thermal regime. Additionally, it was noted that fish spawning lasted longer in waters with higher temperatures.
This study examined and described the basic parameters of the catch-and-release angling of roach Rutilus rutilus and European perch Perca fluviatilis with the mormyshka technique. Catch efficiency, the size of the fish caught, the time required to unhook the fish and the total time during which the fish were handled, hooking location, the occurrence of injury and initial hooking mortality were determined. The study indicates that the mormyshka technique is an effective way to catch roach and European perch when ice fishing. The efficiency of the catches and landings was similar for barbed and barbless hooks. The mormyshka technique also proved to be safe for the fish during catch-and-release fishing. The decided majority of fish were hooked shallowly on the upper jaw, which is a safe location, and injury occurred rarely regardless of the hook type. Generally unhooking the fish from the mormyshka hook was seamless and fish handling was brief. Additionally, when roach were caught with barbless hooks, unhooking time and handling was shorter than it was with barbed hooks. No initial hooking mortality was observed in roach, while it occurred in only two specimens of European perch.
First record of brown bullhead, Ameiurus nebulosus (Lesueur), in the Łyna River drainage basin (northeast Poland)
This paper presents the first records of the occurrence of brown bullhead, Ameiurus nebulosus (Lesueur), in the Łyna River drainage basin. In February 2010, 77 brown bullhead were collected in Lake Czarne, and one in July 2010 was caught by angling method in Lake Długie in Olsztyn (northeast Poland). The specimens collected in Lake Czarne range from 72 to 154 mm total length (TL) and weighed from 3.9 to 36.8 g. Among measurable characters, the greatest variability was noted in head width, preanal distance, and snout length. The least variability in measurable characters was noted with regard to dorsal fin length, eye diameter, and preventral distance. Because of the adverse impact brown bullhead would have on the indigenous ichthyofauna of the Łyna drainage basin, its spreading occurrence in this region is an ecological and economic threat.
Feeding of hatchery-reared juvenile Atlantic sturgeon, Acipenser oxyrinchus Mitchill, released into the Drwęca River
Atlantic sturgeon, Acipenser oxyrinchus Mitchill was once one of the largest European freshwater fish, and it was common in the Vistula River drainage. Since 2006, juvenile Atlantic sturgeon obtained by artificially reproducing wild spawners caught in the St. John River in Canada have been stocked into several rivers in Poland. The current study to assess the feeding of Atlantic sturgeon in the Drwęca River in Poland is part of a larger project to restore the species to this region. Hatchery-reared eleven-month-old Atlantic sturgeon were recaptured 2 to 10 days after their release into the river. This study provides the first data on the diet of A. oxyrinchus in the fresh waters of Europe. In June 2008, the stomach contents of the juvenile Atlantic sturgeon that had been recaptured were collected using gastric lavage. Of the 70 sturgeon the Drwęca River which were subjected to gastric lavage, 67% of them had empty stomachs. The diet of juvenile Atlantic sturgeon consisted of nine taxa of prey. Primarily, sturgeon eat small, soft-bodied larval Oligochaetae and Chironomidae.
The aim of the study was to determine the degree of overlap in the feeding niches of early developmental stages of roach, Rutilus rutilus (L.), perch, Perca fluviatilis L., bleak, Alburnus alburnus (L.) and sunbleak, Leucaspius delineatus (Heckel). The hypotheses were that (i) larvae of different fish species of similar body sizes feed on similar food, and that (ii) smaller fish compete with larger ones for similar prey. The results of the analysis was to answer the question of whether the diet overlap of juvenile fish stages decreases with ontogenetic development. The study was conducted for two years (2001-2002) in two shallow, polymictic, eutrophic lakes. The diets of early developmental stages of fish species of similar body sizes differed. The few instances of diet overlap resulted from the abundance of food resources in the environment. However, fish of smaller body sizes exploited the same food resources as did individuals of the same species that belonged to different cohorts.
This paper discusses the problem of the occurrence of non-native fish species in a strongly transformed aquatic ecosystem. The changes in this ecosystem are caused by warm water discharges from two electric power plants. Twelve non-native fish species are confirmed to occur in the system of five heated lakes located in central Poland. In total, 30% of the total number of non-native species confirmed in Polish inland waters were noted. Aquaculture and fisheries are the primary sources of non-native species in these lakes. Among the species identified, most reached the lakes or canals by escaping from farming facilities or through commercial stocking. Four species have established stable populations. Pseudorasbora parva (Temminck & Schlegel), Carassius gibelio (Bloch), and Carassius auratus (L.) are invasive species that occur abundantly in all the lakes, while Cyprinus carpio L. reproduces irregularly and only in the most heated lakes. The remaining species do not reproduce in the heated lakes system, or anywhere else in Poland; still, the threat these species pose must not be underestimated.