Water temperature differences in interfluvial palm swamp habitats of Paracheirodon axelrodi and P. simulans (Osteichthyes: Characidae) in the middle Rio Negro, Brazil

Abstract

The cardinal (Paracheirodon axelrodi) and green neon tetras (P. simulans) are ornamental fish species which occur separately in two different types of palm swamp habitat in the middle Rio Negro, Amazonas State, Brazil. These palm swamp habitats are part of extensive interfluvial regions which flood as a function of seasonal precipitation and remain flooded in some regions even during dry periods, due to a high water table and waterlogged, hydromorphic soils. Hydrostatic sensors installed in P. axelrodi and P. simulans habitats recorded daily changes in water level and water temperature every 15 minutes during a 5-month period between September 2009 and January 2010. Significant differences in water temperature were encountered between the two habitats, especially in regards to maximum daily water temperatures. In P. simulans habitats water temperatures ranged from a low of 24.6 to a high of 35.2 °C, while in P. axelrodi habitats temperatures varied between 25.1 and 29.9 °C. The high values recorded at P. simulans sites may indicate a possible thermal tolerance to extreme temperatures, which could partially explain the segregation of the two species in distinctive interfluvial habitats. © 2011 by Verlag Dr. Friedrich Pfeil.