Dynamic phase portrait: New possibilities of detecting changes in populations

This paper demonstrates the possibilities of detecting changes in populations of animals, based on the analysis of their dynamic phase portrait. This method allowed us to clarify the periodization of the process of naturalization of the Black Sea sprat (Clupeonella cultriventris) in the Rybinsk Reservoir and in detail describe the changes in the main dynamic characteristics of the population. On the example of zander (Sander lucioperca) in Lake Vozhe, the state was observed in which intra-population mechanisms activate which slow the increase in population (distribution of individuals from regions with high density). Use of this method allowed us to describe the new stable state of the population of grayling (Thymallus thymallus), which it entered as a result of increase in sport fishing. The data on time of presence of a population in equilibrium state allowed us to correctly unify the materials used for the analysis of changes in its age group.

LONG-TERM DYNAMICS OF CATCHES, ABUNDANCE AND BIOMASS OF ZANDER (SANDER LUCIOPERCA L.) POPULATION IN BELOYE LAKE

Until the end of the 20th century fish community in Beloye Lake had been mainly presented by smelt and zander, which resulted in the high volumes of the species catches, yearly variations changed synchronously. Dynamics of zander and smelt fishing in Lake Beloye in the period from 1940 to 2017 has been described. Since 1970s the volumes of their catch and the share in total catches have become gradually decreasing. The average catch made by the research trawl during 1 hour is taken as the main indicator of long-term fluctuations of abundance and biomass of zander population in Beloye Lake within 1970-2017. The main reason for the long-term decline of abundance of smelt and zander populations is the global warming. Smelt biomass rapidly declines in hot years, which results in a sharp decrease of the zander feed supply. The 6-7-year periods of massive reduction of abundance, biomass and catches of zander and smelt in Beloye Lake were recorded in the 1970s and 2000s. Against a background of a sharp decrease of smelt abundance, in 2001-2003 in Beloye Lake there were registered the most numerous zander generations, which caused a strong population imbalance. Thus, the abundance of small-sized fish increased in the 2000s and the commercial biomass of the population decreased rapidly, which led to a significant reduction of zander catches. Generally, against the outlined trend of climate warming, there grows the risk to lose the commercial status of reservation of the commercial status of smelt and zander populations in Beloye Lake in the future.

Comparative analysis of branchial ionocytes in Caspian Sea zander, Sander lucioperca (Linnaeus, 1758) using Na+, K+-ATPase immunolocalisation at different salinities

Gill morphology and branchial ionocyte variability were examined in zander Sander lucioperca (Linnaeus, 1758)fingerlings, having two different body weights (1 and 2 g) for a period of ten days following their transfer from freshwater to two different salinities (7 and 12‰ Caspian Sea water) using Na+, K+-ATPase (NKA) immunolocalisation. Survival rates and plasma osmolarity levels at the end of each salinity challenge were measured. By the end of the experiment, bothweight groups were able to survive and successfully acclimate to salinity change. The number and size of branchial ionocytes in the gills dramatically decreased in both size groups; while, the filament ionocytes in both weight groups reformed at the end of the acclimation period. The results indicated both groups to be in the same osmoregulatory developmental stage, despite difference in their body weight. Also, their blood osmotic pressure and gill ionocyte changes at different salinity were similar when transferred to iso-osmotic condition. Further studies are needed for complete understanding of zander osmoregulatory systems exposed to different salinities.

Quality in use and nutritional value of the muscle tissue of zander (Sander lucioperca) and pike (Esox lucius) reared in polyculture

The research objective was to compare the quality in use and nutritional value of muscle tissue of zander (Sander lucioperca) and pike (Esox lucius) reared in a polyculture. The research material comprised 16 specimens (8 of each species) captured from one pond in a fish farm situated in the Lublin Voivodeship. The fish were of similar age. The pike, while having a higher body weight, had a higher percentage of guts, and the carcass percentage and a Fulton’s condition coefficient were lower than in the zander. The chemical composition and calorific value of the muscle tissue were very similar for the two species (water 76.40% and 77.15%; protein 21.26% and 21.41%; lipids 0.41% and 0.58%; ash 1.43% and 1.42%; and energy 517 and 528 kJ/100 g for zander and pike, respectively). It is worth noting the high INQ value for the protein of both fish species (6.8 for pike and 6.9 for zander), which indicates that a 100 g portion of zander or pike fillet is a valuable source of protein in the human diet.