Feeding patterns and seasonal variation in the diet of non-indigenous fish species Lepomis gibbosus L. from shallow eutrophic lakes along River Vit, Bulgaria.
Non-indigenous fish species pumpkinseed, Lepomis gibbosus L. is the most abundant species in investigated shallow eutrophic lakes, part of pond's system ("adaptive ponds") serve as a buffer zone between the oil refinery "Plama" (city Pleven) and the River Vit (North Bulgaria). In the present study food choice of Lepomis gibbosus were investigated. Fishes were collected in March, May, July and November 2007-2008. Gut analyses of 379 pumpkinseed and 53 samples from co-existent fish species (Perca fluviatilis, Scardinius erythrophthalmus, Pseudorasbora parva, Carassius sp., Leuciscus cephalus) was done. Food analyses were showed 23 groups of food items. It is not observed significant differences in feeding between different age classes. The diet of all age groups consisted mainly of Chironomidae (Diptera) larvae. Only in age group 2+ Cladocera dominated. The diet of Lepomis gibbosus showed some seasonal variations. Chironomidae, Copepoda (Cyclopoida, Calanoida, nauplii), Cladocera, Tipuliidae (Diptera) were presented relatively equally in May, while Chironomidae played a leading role in July and March. Diet overlaps between Lepomis gibbosus and other fish species were discussed. Interspecific competition was suggested with Pseudorasbora parva. The observed relatively low growth rate can be explained with high intraspecific competition.