The locations were then grouped with the aid of multi-variate analysis depending on species composition and and the number of fish caught in each net.8 different fish communities were found to exist in the inlet. Each fish was determined to species, weighed, and measured in lengtht, whereupon a condition factor was calculated. Analysis of stomachs and age determination was made for perch in order to study food preference and age composition in the different groups. Perch went through two major shifts in food preference. Plankton was a food item up to 10 cm of lenght perch, whereupon a benthos-feeding stadium took place. The perch then changed to a diet mainly consisting of fish at a length of 17,5 to 22,5 cm.
One of the effects of eutrophication is increased water turbidity, whereupon roach is thought to be favoured in competition with the visually hunting perch. In a brackish water system, where other species of prey exists for both perch and roach, a greater separation of niches takes place, compared to limnic systems. This separation of niches results in perch catches of mysids, polychaetes and gobies along with a great deal of chironomids. None of the three first mentioned lives in fresh water.
The roach, in turn, feeds to a great deal upon the mollusc Hydrobidae, which is not occuring in fresh water. It is furthermore a species group which is favoured by eutrophicated waters. These facts imposes that the interspecific competition roach vs. perch is not as hard in brackish water systems as in limnic systems, and the perch therefore never is competed out. The only areas of the inlet in which a dominance of cyprinids existed were the inner areas, i.e. Dynestadsviken and Dynestadssj�n. These areas are probably very much like a limnic system, with a great load of nutrients. This is consitent with that mainly few, large piscivorous perch was caught in these areas. In the other areas of the inlet, no such effect of euthophication was found. Thus, eutrophication is not an important factor determining the composition of fish communities in brackish waters, which is in difference to limnic areas.
Alla f�ngade fiskar artbest�mdes, v�gdes och l�ngdm�ttes, varefter kondition ber�knades. Maganalys och �ldersbest�mning utf�rdes p� abborre f�r att studera dess f�dopreferens och �ldersstruktur i de olika fisksamh�llena. Abborren genomgick tv� st�rre f�doskiften, till en del gradvist �verg�ende i varandra. Abborre upp till en l�ngd av 10 cm �t mycket plankton, varefter ett benthos-�tande stadium tog vid. Abborren gick sedan �ver till en diet �verv�gande best�ende av fisk vid en l�ngd av 17,5- 22,5 cm.
En effekt av �vereutrofiering i s�tvatten �r att turbiditeten �kar, varefter m�rten tros konkurrera ut den visuellt jagande abborren. I brackvattensystem, d�r andra byten finns f�r b�de m�rt och abborre, kan en st�rre nischseparation ske. Denna nischseparation best�r till en viss del av att abborren har m�jlighet att anv�nda en st�rre diversitet av byten, fr�mst pungr�kor, havsborstmaskar och sand- och lerstubb, vilka ej finns i s�tvatten. Den �ter �ven mycket fj�dermygglarver.
M�rten i viken �ter till stor del den eutrofieringsgynnade Hydrobia-sn�ckan, som ej heller finns i s�tvatten. Detta medf�r att konkurrensen mellan m�rt och abborre inte blir lika h�rd, och abborren konkurreras d�rf�r ej ut. De enda delar i viken d�r dominans av cyprinider p�visades var de inre, dvs Dynestadssj�n och Dynestadsviken. H�r r�der troligen n�rmast limniska f�rh�llanden, och n�rsaltsbelastningen �r h�g, vilket g�r att endast ett f�tal st�rre, fisk�tande abborrar finns h�r, med ett f�tal undantag. I �vriga viken, som ocks� karakteriseras som eutrofierad, blir eutrofieringens effekter p� fisksamh�llena inte lika stora. Eutrofieringen har allts� inga st�rre effekter p� konkurrens arterna m�rt och abborre emellan i ett brackvattensystem.