Reviews in Fish Biology and Fisheries 10: 61–89, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 61 Is density-dependent growth in young-of-the-year fishes a question of critical weight? J.H. Cowan, Jr. 1 , K.A. Rose 2 & D.R. DeVries 3 1 Department of Marine Sciences, University of South Alabama, Mobile, AL 36688, USA (Phone: (334) 460- 7136; Fax: (334) 460-7357; E-mail: jcowan@jaguar1.usouthal.edu); 2 Coastal Fisheries Institute and Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, LA 70803-7503, USA; 3 Department of Fisheries and Allied Aquacultures, Auburn University, Auburn, AL 36849-5419, USA Received 5 January 2000; accepted 3 April 2000 Contents Abstract page 61 Introduction 61 Conceptual arguments and exposition of premise 62 Evidence from selected individual-based models 68 Summary and chronology of the literature 74 Empirical evidence from freshwater systems 74 Empirical evidence from marine systems 76 Discussion 77 Acknowledgements 80 Appendix 81 References 82 Abstract We develop a conceptual argument that density-dependent growth via reductions in prey resources are most likely to occur in the late-larval or juvenile stage in both marine and freshwater fishes. We use results from a suite of individual-based models and literature examples of a variety of marine, estuarine and freshwater species to provide evidence of the effects of age-0 fish on their prey. We conclude that larval-stage survival related to food- limited growth contributes significantly to recruitment variability. However, density-dependentregulation of cohort biomass via feedbacks derived from reductions in prey resources is most likely to occur at a “critical-weight” during the late-larval or juvenile stage. This occurs when fish densities remain relatively high, and population consumption is highest relative to prey density and replenishment rate. We compare our critical weight concept to Houde’s (1997) critical size hypothesis. Introduction High fecundities of fishes ensure high early life stage abundances that are subject to both density- independent controls responsible for variability in recruitment, and density-dependent regulation that stabilizes recruitment (Cushing, 1974; Rothschild, 1986; Houde, 1994). Information on growth rate- mediated effects of food limitation on mortality and recruitment variability is pervasive in the marine fish literature (see Heath, 1992; Leggett and DeBlois, 1994; and Table 1 for review). These effects have been the cornerstone of many “recruitment hypotheses” including Hjort’s (1914) critical period, Cushing’s (1975) match/mismatch, Lasker’s (1978) stable ocean, and Houde’s (1989) stage duration hypotheses (see Leggett and DeBlois, 1994 for review). Density- dependent growth due to competition for food can