BACKGROUND: Parasite effects on biometric characteristics of common carp, C. carpio from Anzali Wetland. OBJECTIVES: Identifying parasites in C. carpio and evaluating their effects on biometric characteristics of fish. METHODS: A total of 78 individuals were collected on the seasonal basis (from spring through winter 2016) from the wetland, transported to the laboratory and after biometry, dissected to recover parasites. Cestodes and trematodes were stained with alum carmine and nematodes were cleared with glycerin alcohol, then their prevalence, abundance and mean intensity were determined. RESULTS: Thirteen parasite species including Ichthyophthirius multifiliis, Trichodina sp., Epistilis sp., Gyrodactylus sp., Dactylogyrus extensus,  Diplozoon nipponicum, Diplostomum spathaceum, Posthodiplostomum cuticola, Asymphlodora sp., Caryophyllaeus fimbericeps, Raphidascaris acus, Pseudocapillaria tomentosa and Lernea cyprinacea were identified. Epistylis sp., P. cuticola, Asymphlodora sp. and P. tomentosa are reported for the first time from C. carpio in Anzali Wetland. The average weight in healthy and infected fish were recorded to be from 23.68 ± 3.54g to 686.73 ± 100.28 g, and from 32.47 ± 4.51 to 633.62g ± 64.64 g respectively. The condition factor in healthy and infected fish was from 1.09 ± 0.50 to 1.17±0.03, and from 1.24 ± 0.13 through 1.19 ± 0.03 respectively. It was also true for gonadosomatic index which was recorded in healthy and infected fish from 0.45 ± 0.16 through 3.56 ± 3.54, and from 1.78±0.67 through 2.74 ± 0.62. The instantaneous growth rate was 1.25 in healthy  2+ and 1+ year old individuals, and 0.72 in 3+ and 2+ year olds, while it was 0.94 and 0.65 in the same-aged infected fish, respectively. CONCLUSIONS: Parasites could induce some negative influences on the biometric characteristics of infected fish, decreasing their growth rate. So that, it is necessary to monitor the parasite communities continuously in the native and commercially important fish species in Anzali Wetland to protect them and prevent introducing infected fish into the adjacent fish farms.