Changes resulting from logging modify the physical structure of stream habitats indirectly, and consequently the ecomorphological structure of fish assemblages. The present study aimed to evaluate the effect of changes in the physical structure of the habitat resulting from conventional logging (CL) and reduced-impact logging (RIL), in the ecomorphological structure of the fish assemblages of streams of the Eastern Amazon, verifying (1) which variables of the physical structure of the habitat are associated to the different methods of exploration; (2) if there is a difference in the ecomorphological structure of the fish assemblages of the different treatments, and
(3) which ecomorphological characters are associated with physical variables of the habitat. In each stream 14 physical variables of the habitat were measured, as well as fish samples collected using hand nets. The collected specimens were affected in Eugenol, fixed in 10% formalin and after 48h transferred to 70% alcohol. Possible differences in habitat structure and ecomorphological structure of fish assemblages between treatments were evaluated by Multiple Linear Discriminant Analysis (MLDA). The relationships between the habitat variables and the ecomorphological characters were evaluated through Redundancy Analysis (RDA). The structure of the streams habitat differed among all treatments, with control areas showing higher vegetation cover and higher average substrate size. As for ecomorphology, we also found that there was a difference in ecomorphological structure among all treatments. In EC environments, species with greater relative head length, with the wider pectoral fin and with more compressed caudal peduncle were predominant in these environments; in control areas, species with wider mouth were favored; and in RIL areas, more flattened species were predominant. Logging affects the habitat structure of the streams, resulting in loss of plant cover and average substrate size. There was a reduction of plant cover and average substrate size in areas of EC and RIL areas. In this sense, it is believed that both the EC and the RIL have the potential to alter the ecomorphological structure, and consequently the ecosystem services provided by the assemblages of fish from streams in the Amazon. So even if EIR reduces damage to forests, it is failing to protect the ecosystems of streams, since changes have been observed in these environments when compared to control areas. However greater efforts should be employed to fully understand such a relationship and proportions that the damage can cause to the ecosystem.
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