Young of the year (YOY) tenches (Tinca tinca L.) were caught in relatively great number in Tisza-Lake at the Tiszafüred section on last days of October in 2004. The standard length of these fishes varied between 20 and 46 mm. It seemed that the collected sample could provide appropriate data to examine the size-structure of YOY tenches, so we...measured their standard body-lengths in mm and -weights in hundred parts of gramm unit. After the statistical analysis were found the follows:
1. The curve of length frequency corresponds with normal distribution, i.e. there was not found multimodal curve as could be expected in the case of a periodic spawning species.
2. The average standard length of the examined individuals – although the environmental conditions of the population is good – was only 31 mm. It is far below the 37 mm average of the lowest growth of tench population was found in the scientificpapers.
3. More than 20% of measured sample belonged to the range of 20-26 mm. The estimated ages of these fish specimens are about 70 days, according the scientificpapers.
By right of above mentioned can be concluded that the sample represents only one age-group from a late spawning, and not the whole range of YOY tenches, so these data can give information about the size structure only of this group. The 31 mm average standard length of individuals, origin from spawning in late July or beginning of August is accordance with age and environmental conditions as well.
The increase of species richness in communities of natural biogeographic regions in an anthropogenic way can be expressed as biogeographic pollution. Where there is contaminated fauna, one must investigate how this occured. I studied how the members of Hungarian fishfauna could be present resident and have managed to workout a so-called system...of fauna component conception which is suitable for this requirement.
The expression of ’faunacomponent’ includes other expressions. That kind of species belong to a certain faunacomponent that reached the studied area in the same way. Species reached the studied area without an anthropogenious contribution are qualified as native fauna components. These kind of species are endemic species, occasional species and settlers. In contrast to native faunacomponents, some kind of human influence is always detectable in connection with the way reached the studied area by non-native species. Accordingly, group of non-native species includes directly or indirectly facilitated settlers, species that are introduced accidentally and those introduced intentionally. It is obvious that classifying a given species could be construed solely in connection with a certain area.
Applying Shannon diversity index I have initiated the assemblage natural index (ANI) in order to show a way how to use the system of faunacomponent conception in practice. ANI refers to the degree of naturalness of faunistical samples. If ANI > 1 it means there are not any non-native species and ANI < 1 it means there are some non-native species in the sample respectively. In the latter case ANI decreases proportionally with the number of non-native species and specimens. In that special case when only one specimen of only one non-native species can be found in the faunistical sample ANI = 1.