Variation in water colour is a remarkable characteristic of Amazonian rivers and reflects their limnological properties and the geomorphology of sub-basins. We present here a literature-based study to examine the relationships between fish species turnover and abiotic properties of Amazonian rivers with contrasting water colours. We analysed fish records and water physicochemical properties (pH, colour, turbidity, dissolved oxygen, ammonia and suspended solids) of eight Amazonian rivers with white-, black- and clearwaters. Rivers with similar water colour shared more fish species than those that contrasted in colour. Increased differences in abiotic parameters imply an increased dissimilarity in fish species composition. Species composition is also related to distance among rivers with high dissimilarity observed in rivers distant to each other. The fish species turnover could be ultimately driven by the geological history of rivers which provides different opportunities to speciation and biotic interchange. Water types likely influence species turnover by selecting fishes with different limits of physiological tolerance and specialized use of different habitat types. Our findings suggest that river water colours are reliable proxies for historical and ecological mechanisms affected fish species distribution. Antropic disturbances of Amazonian rivers with distinct water colours could threaten unique fish assemblages.

Antarctic marine invertebrates from the Western Antarctic Peninsula (WAP) are generally stenothermal, with three-month survival and activity limits above the average maximum summer seawater temperature (1.0°C) of 1–6°C and 1–3°C respectively. For many of these species to survive the warmer maximum temperature at the sub-Antarctic island of South Georgia (5°C), they require either greater thermal flexibility, or must avoid the warmest water-masses. The mean depths and depth range of WAP gastropod and bivalve molluscs were compared with the mean depths of these same species at South Georgia; separated into water masses delimited by the 1°C isotherm at South Georgia, surface Antarctic water (SAW < 90 m), winter water (WW 90–150 m) and circumpolar deep water (CDW > 150 m). Bivalves in the SAW and CDW categories at the WAP were centred around the cooler WW (< 1.2°C) at South Georgia, with a narrower mean depth range for CDW bivalves. There was no difference in the average depth of gastropods, but a reduced depth range in the CDW. The apparent temperature limit to bivalve mean depths and not gastropods at South Georgia, suggests that further latitudinal comparisons could yield information on the underlying physiological mechanisms determining the range limits of Southern Ocean fauna.