ECOTOXICOLOGY AND ENVIRONMENTAL SAFETY 19,285-29 1 (1990) Effect of Stress on a Freshwater Benthic Detritivore: Scope for Growth in Gammarus pulex LORRAINE MALTBY, CAROLINE NAYLOR, AND PETER CALOW Department ofAnimal and Plant Sciences, University of Shefield, Western Bank, Shefield. SIO ZTN, United Kingdom Received January 25, I989 Scope for growth (SE), a measure of energy balance (between food intake and metabolic output) within animals, has been used as an indicator of pollution stress in marine systems. However, it has not been used commonly in freshwater systems and here we investigate the sensitivity of SfG in Gammaruspzdex, a benthic freshwater crustacean, under conditions often associated with pollution. The effects of four specific substances were investigated; a metal (zinc), an organic (3,4dichloroaniline), and two dissolved gases (oxygen and ammonia). In all cases SK? was reduced by the stress,primarily due to a depression in energy intake. Only with ammo- nia was energy output (respiration) significantly affected. 0 1990 Academic PWS, Inc. INTRODUCTION Scope for growth (SfG), the difference between energy absorbed (A) and energy metabolized (R) by an animal, can be used to give an indication of its metabolic condition, i.e., how much energy is available for growth and reproduction (Warren and Davies, 1967). SfG has been used as an indicator of stress in a number of marine invertebrates and appears to be sensitive to a wide range of factors (Table 1). Despite this large body of work on marine invertebrates, few studies have investigated SG in freshwater invertebrates. A scope for growth assay has recently been developed using the freshwater amphi- pod Gammaruspulex (Naylor et al., 1989) and the aim ofthis study was to investigate the response of this assay to a range of stresses, i.e., a metal (zinc), an organic toxin (3,4-dichloroaniline), and two dissolved gases (oxygen and ammonia). MATERIALS AND METHODS Only males (7-10 mg dry weight) were used as experimental animals and these were collected from an unpolluted stream in Derbyshire (UK). Details of holding conditions and pretreatment are given elsewhere (Naylor et al., 1989). The assay consisted of a &day period of exposure to the stress, over which energy absorption was measured, plus a 1 -day exposure when respiration rate was measured. Full details of the techniques used are given in Naylor et al. (1989) and only devia- tions from these methods are described here. All experiments were performed at 15”C, using 20 animals per treatment and food was presoaked in the test solution for 4 days prior to use. Test Solutions All solutions were made up using “artificial pond water” (Naylor et al., 1989) as the dilution medium (pH 7.6, alkalinity 48.8 mg HCOJliter, Ca2+ 80 mg/liter). 285 0147-65 13190 $3.00 Copyright 0 I990 by Academic Press. Inc. . .. . . . e ,_.. *