Feeding activity of spined loach Cobitis sp. in Lake Lucień, Poland

The feeding activity of spined loach Cobitis sp. was studied in post-glacial ribbon Lake Lucień, Central Poland, during three 24 hrs periods in May, August and September. Samples were taken every 4 hrs and 8 to 18 (mode 10) specimens were caught on each sampling occasion. A total of 233 fish (37.3-107.6 mm TL) gut contents were examined. Six main food components (Cladocera, Chironomidae (larvae and pupae), Copepoda, Ostracoda, other macroinvertebrates and detritus) were used by the fish. Precise identification of gut contents showed that spined loach consumed large numbers of food items (from 31 to 39). Nevertheless standardised form of Levin's and Shannon-Wiener's indices revealed a rather narrow food niche, which was a result of unequal proportions of food items in gut contents and domination of few prey categories. Spined loach fed mostly from post-dusk to dawn and achieved maximum gut fullness in the morning (4.00-8.00). This nocturnal feeding pattern was consistent throughout all sampling occasions, but there was some discrepancy concerning 12.00 hours in spring and summer. Due to this, early morning activity can not be excluded. Prey selection indices indicated that spined loach preferentially consumed some small size chironomids: Tanytarsus, Cladotanytarsus, Dicrotendipes and avoided larger ones (Glyptotendipes, Stictochironomus).