The most important results about structure and functional state of small rivers ichtyocenosis from Republic of Moldova are reported in this paper. On this base it was posible syntesis made of some postulates which reflect ichtyofauna situation of this aquatic ecosystems, in present being strong affected by anthropogenous factor. It has been approached stability, bioindication and bioinvasive problems in small rivers ichtyocenosis. Also, has been emphasized biotopic diversity importance as inalienable component of specifically diversity and that ecosystem functionality is expressed by means of its integrity.