The Growth of Brown Trout (Salmo trutta fario L.) in Different Climatic Regions of Lithuania

The growth rate of brown trout (Salmo trutta fario L.) varies across its distribution range, as well as in the rivers of three different Lithuanian climatic regions. Interspecific and intraspecific competition that is closely related even to minor climatic differences is considered to be one of the major factors determining differences in trout growth. The highest significant (p < 0.05) growth rate was found in juvenile trout at the age 0+ and 1+ in the rivers with the lowest species richness, whereas the growth rate in trout at the age 2+ and over was highest in the rivers with the highest species richness. No statistically significant correlation between trout size and density in different age groups was found in the investigated climatic regions of Lithuania, spare environmental capacity probably plays the major role here. However, significant differences in different age groups were observed in trout size and species richness, which attests to the impact of interspecific competition on trout growth.