We evaluated the relative weight (Wr) condition index for assessment of growth, prey availability and environmental conditions in fish populations. Standard weight (Ws) equations for pumpkinseed (Lepomis gibbosus) and golden shiner (Notemigonus crysoleucas) from 302 pumpkinseed and 285 golden shiner populations, with well over 10,000 fish of each species, were developed with regression-line-percentile (RLP) technique. The proposed Ws equation in metric units for pumpkinseed is log10Ws = -5.179 + 3.237 log10TL, and for golden shiner is log10Ws = -5.593 + 3.302 log10TL. The English-unit versions of these equations were also developed. Evaluation of relationships of Wr with fish growth and other ecological variables were made from ten southern Quebec lakes in 1987 and 1988, with over 2,000 fish of each species. Size-specific growth and size-specific Wr were calculated using stock and quality length of each species. Lake, year, season, and length affected Wr, but not sex of fish. No significant relationships were found between Wr and growth among lakes or among individual fish. Significant correlations were found between Wr and prey availability and chlorophyll a, but not fish biomass, macrophyte biomass, and temperature. Our results suggest that Wr can reflect prey availability of fish populations better than other physiological or ecological conditions of fish. We recommend that Wr be used cautiously as an assessment tool in freshwater fishes
