Krystyna Maciejewska, Piotr Margońskii
Sea Fisheries Institute, Kołłątaja 1, 81-332 Gdynia, Poland

Key words: Chaetognatha, Sagitta elegans, Sagitta setosa, southern Baltic Sea

Abstract.
The occurrence of chaetognaths (Sagitta elegans and Sagitta setosa) was analyzed in three regions of the southern Baltic Sea: the Bornholm Deep, the Słupsk Furrow and the  Gdańsk Deep. It was confirmed that chaetognaths are brought into the Baltic with inflows of saline waters from Kattegat. From the moment of inflow chaetognaths do not feed, or do so sporadically, and neither their size structure nor their gonadal development stage change. Based on this information, it can be stated that chaetognaths in the Baltic are allochthonous and that they constitute a pseudo-population which is renewed with saline water inflows from Kattegat.