By Ibemenuga, Keziah Nwamaka
The macro-invertebrate fauna of Ogbei stream in Nkpologwu, Aguata local Government Area, Anambra State, Nigeria was studied between May 2002 and April 2003. six stations were selected for the study of physico-chemical and biological factors in relation to depth, human activities and land influence in the different stations. Analyses of the physico-chemical parameters indicated that water temperature fluctuated between 24.8' C and 28.7' C with an annual mean o f 2 7.47k0.79. Dissolved o xygen ranged from 3.8 mg/l in March to 6.5 mg/l in August with an annual mean of 5.14*0.69. Depth ranged from 0.38 m in March to 0.72 m in August with an annual mean of 0.54*0.07. Water transparency varied between 16.3 cm in
September and 33.9 cm in March with an annual mean of 26.73*3.59. Free carbon dioxide ranged from 4.0 mg/l to 39.2 mg/l in August and February respectively. The annual mean was 11 -60k6.49. Alkalinity fluctuated from 24.3 mgA CaC03 to 55.0 mg/l CaC03 in August and October respectively with an annual mean of 33.25k6.53. A total of 11420 macro-invertebrates
belonging to 4 classes, 13 orders, 29 families and 51 species were collected. Insecta (11225, 98.29%) was the most abundant class, followed by Arachnids (92, 0.81%), Oligochaeta (75, 0.66%) and Crustacea (28, 0.25%). Diptera was the most abundant order with a percentage composition of 42.62%, followed by Odonata (36.89%), Coleoptera (9.76%), Hemiptera (8.22%) and Plesiopora (0.66%). Composition and distribution of macro-invertebrates indicated that
station 3 had the highest percentage composition and abundance of 28.56% (3262), followed by station 2 with 19.54% (2232). Station 5 had the least value of 9.39% (1072). There was a positive correlation between macro-invertebrate abundance and air temperature (r = 0.428), water temperature (r = 0.590), transparency (r = 0.422) and free carbon dioxide (r = 0.305). The
effects of the physico- chemical parameters on the aquatic macro-invertebrate population in the stream were discussed.