Is fish condition correlated with water conductivity? G.H.C OPP CEFAS, Salmon & Freshwater Team, Pakefield Road, Lowestoft, Suffolk, NR33 0HT, U.K. (Received 18 November 2002, Accepted 16 May 2003) There were no correlations between fish condition (K) and water conductivity in 14 species of 0þ year fishes in the River Great Ouse, U.K., catchment. Values of K increased with increasing distance from river source in dace Leuciscus leuciscus and roach Rutilus rutilus. # 2003 British Crown copyright Key words: distance from source; filamentous algae; geographical growth variations; River Great Ouse; water velocity; young-of-the-year. A relationship between body condition and water conductivity has been reported for some freshwater fish species, e.g. brown trout Salmo trutta L., blacknose dace Rhinichthys atratulus (Hermann) and spotted bass Micropterus punctulatus (Rafinesque) (Mebes, 1992; Ha¨nfling, 1993; Dennis et al., 1995; DiCenzo et al., 1995; P. Tucker & C. Richards, pers. comm.), with water conductivity used as a surrogate (or correlate) of water productivity. Should this relationship be universal across a species’ native range, and indeed applic- able to a large number of species, it would be of practical use to freshwater fisheries scientists in assessments of fish growth in relation to environmental conditions. This is particularly true for evaluation of overwinter recruitment potential in young-of-the year (YOY, 0þ year) fishes, which is influenced by body condition at the end of the first summer of life (Bystrom et al., 1998). In lake sturgeon Acipenser fulvenscens Rafinesque this relationship existed in east- ern but not western North American populations (Fortin et al., 1990); in the bullhead Cottus gobio L. it was observed in Flemish but not German popula- tions (Knaepkens et al., 2002); in Mediterranean barbel Barbus meridionalis Risso, no relationship was found in three contiguous Iberian river catchments (Vila-Gispert & Moreno-Amich, 2001). To examine the potential wider applicability of this relationship, correlations betweenwaterconductivityandfishconditionweretested,usingbodymass,standard length(L S )andenvironmentaldatacollectedduringastudyin1990offishes(mainly Tel.: þ44(0)1502562244;fax: þ44(0)1502513865; email: g.h.copp@cefas.co.uk JournalofFishBiology (2003) 63, 263–266 doi:10.1046/j.1095-8649.2003.00145.x,availableonlineathttp://www.blackwell-synergy.com 263 # 2003BritishCrowncopyright