This study determined the contents of cadmium (Cd) in the muscles, ovaries, and eggs of silver female European eels. The analysis of cadmium content was performed on female European eels caught during commercial fishing in freshwater in Warmia and Mazury (Poland), and then subjected to artificial maturation and ovulation processing under controlled conditions. The content of cadmium (Cd) in the tissues was determined by flameless atomic spectrometry using an electrothermal atomizer. The analysis showed statistically significant differences between the cadmium content in the muscles, ovaries, and eggs (p < 0.05) of female European eels. The lowest cadmium content was found in the muscle tissue (0.0012 ± 0.0001 mg kg⁻¹ wet weight) and the highest in eggs (after ovulation) (0.0038 ± 0.0007 mg kg⁻¹ wet weight). Moreover, a relationship was found between the cadmium content in the muscle tissue and the ovaries (R = 0.673; p = 0.0117) in the same fish. The movement of cadmium from tissues to oocytes may indicate a significant problem concerning this heavy metal content in the reproduction of European eel.

Common carp (Cyprinus carpio L.) as a cultivated fish species has huge importance all over the world. According to FAO statistics, carp is the third most widely bred freshwater pond fish species; only two other Cyprinids (silver carp and grass carp) are bred in higher amounts. Carp is native all over Asia and in a large part of Europe. As a result of human intervention, at present, carp are widespread all over the world, except for the Arctic region. Carp breeding was launched in the antique period, in the ancient Chinese Empire and the Roman Empire. The presently applied method of breeding of common carp has a long evolution. From the effectiveness point of view, the propagation and early-life nursing are crucial parts of carp production, as they provide seed stocks for the further growing section. Without effective propagation, there is no intensive carp production. Nowadays, more advanced propagation methods are available all over the world; however, in the current review, only the main milestones and production efficiency of the propagation and nursing method used in the ponds of Eastern Central Europe are discussed. In the historical overview of carp reproduction, first the natural reproduction, then the semi-extensive and intensive hatchery propagation are presented and investigated in detail. The analysis focuses on the advantages and disadvantages of the method. In particular, the different important milestones of the advanced hatchery method are shown and explained. The effectiveness is proven even with practical calculations. Not only the reproduction, but the pond nursing method is also presented and discussed, concentrating on the management of evolutionarily adapted natural feeds (Zooplankton) and their effect on the survival of fish larvae.

In the Central European region, there is a long tradition of breeding fish in artificially constructed ponds. As the area belongs to the temperate zone, farmed fish need to survive cold winter periods. Common carp (Cyprinus carpio L.), which is an omnivorous, bioturbating species, is well adapted to warm and cold periods and the alluvial water environment. Since the Middle Ages, a large scale, efficient carp farming methodology has been developed in the region, where production is based on natural resources (protein and fatty acid sources) of renewable water ecosystems. This summary aims to present this well-developed breedi:ng method through discussing aspects of hydrobiology and energy transfer through the food chain as well. Capabilities and effects of agro-technical treatments such as liming and organic manuring, zooplankton management and possible supplementary feedings are also reviewed. Analysing chemical processes of waters uncovers that biological production has no carbon footprint; no carbon dioxide is released into the atmosphere. In contrast, gaseous carbon dioxide diffuses into pond water containing calcium and/or magnesium, then it accumulates in algae production and, through energy migration to upper trophic levels, increases carp production. Thus, it can be declared that pond-farmed carp provides an environmentally friendly, delicious meat among products of animal origin.