There is great variation in the conservation status of the last habitats with long-term natural viable populations of the salmon species Hucho hucho in Maramureş Mountains Nature Park, Eastern Carpathians (Romania). According to the specific guidelines for Natura 2000, 42.11% are in good conservation status, 31.57% are of average status, and 26.32% are in a partially degraded condition. In this study area, 6 main risk elements were identified related to human impact on the environment: poaching, minor riverbed morphodynamic changes, liquid and solid natural flow disruption, habitat fragmentation leading to isolation of fish populations, organic and mining pollution, and destruction of riparian tree and shrub vegetation. All of them have contributed to the decrease of H. hucho distribution in the study area to about 50% of the previous local range. Individuals of this species were recorded in only 21 of the 370 sampling stations.

Three populations of brook trout, Salvelinus fontinalis, established in streams and reservoirs in the Jizersk? Mountains, Czech Republic, were studied between 1995 and 2006. The maximum age was usually 3+ to 4+, but the age 7+ was also recorded. The inflows of all reservoirs are populated mostly by 0+ to 2+ brook trout, while older specimens live in a lentic environment, migrating to lotic habitats only to spawn. The density of brook trout in streams ranged from 8 to 95 individuals per 100 m2 during spring and summer, while that for reservoirs ranged between 31 and 290 individuals per ha. A strong negative correlation between the size of adult fish and population density in reservoirs was observed. The type of management influenced both density and growth of brook trout. Further introduction of this species in the central European area should be restricted to habitats where native salmonids cannot survive, such as acidified waters.

Poor regulated fishery, pollution, fragmentation and loss of habitat are most important factors influencing decline of sterlet population worldwide. In Middle and Lower Danube region, this species still have significant economic importance since wilde populations are commercially exploited, while Upper Danube populations are dependent on stocking efforts in order to maintain their presence in open waters. Aim of present study is to analyze genetic diversity of sterlet populations from the Middle and Lower Danube and Lower Tisza rivers, as a prerequisite for their effective conservation and management. Analysis of a highly variable D-loop fragment of mitochondrial DNA detected five new haplotypes, while the eight previously identified haplotypes had extended their previous range. Genetic variability could be attributed almost entirely to individuals, with observed lack of population structure. Negative values of neutrality test indicate recent expansion on some sampling locations. Adittionaly, gene flow analysis between Lower and Middle Danube region showed intensive exchange of speciemens. At the same time analysis showed some influence of Tisza dam on gene flow between samples from Tisza and Middle Danube section.Our study indicated the need for a careful planning of sterlet stocking programmes and inclusion of demographic data or catch time-series. [Projekat Ministarstva nauke Republike Srbije, br. 173045]

Early aquaculture studies were mainly engaged in practising different culturing systems, primarily focusing on the improvement of fish growth and feed type. The significant advances in molecular biology during the last century greatly influenced the development of genetic research and application of molecular methods in aquaculture and fishery. These methods provided substantial opportunity for increased production efficiency, better product quality and improvement of animal health. Additionally, DNA based methods provided tremendous improvement in species determination, family tracking, pedigree determination of individuals, identification of lineages, identification of markers and loci that are responsible for economically important traits. In this work we pay special attention to the utilization of restriction fragment length polymorphism (RFLP) in aquaculture and fishery as a practical and relatively cheap method for determination of genetic lineages in polymorphic fish species. We also focus on gene expression as an excellent method for understanding physiological processes in fish. Currently, quantitative real-time PCR is one of the most accurate methods for gene expression analysis. It is very precise, sensitive How to cite this book chapter:

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