Table 1. Frequency of occurrence (Fi), volumetric contribution (Vi) and index of preponderance (IP) of major food items consumed by Oreochromis niloticus in Lake Tana, gulf of Gorgora (n = 256)

Food item	Fi	%Fi	Vi	%Vi	%IP
Phytoplankton	197	77	477.9	44.3	52.3
Detritus	154	60.2	276.1	25.6	23.6
Zooplankton	162	63.3	166.7	15.5	15
Macrophytes	107	41.8	117.4	10.9	7
Insect	98	38.3	35.2	3.3	1.9
Nematodes	72	28.1	1.2	0.1	0
Unidentified	62	24.2	3.6	0.3	0.1