Environmental Biology of Fishes 65: 37–45, 2002. © 2002 Kluwer Academic Publishers. Printed in the Netherlands. Juvenile snooks (Centropomidae) as mimics of mojarras (Gerreidae), with a review of aggressive mimicry in fishes ∗ Ivan Sazima Departamento de Zoologia and Museu de Hist ´ oria Natural, Caixa Postal 6109, Universidade Estadual de Campinas, 13083-970 Campinas, S ˜ ao Paulo, Brasil (e-mail: isazima@unicamp.br) Received 10 December 2001 Accepted 15 March 2002 Key words: facultative mimicry, Centropomus mexicanus, Eucinostomus melanopterus, feeding habits, social behaviour Synopsis Aggressive mimicry has been proposed for several unrelated fish species both in freshwater and marine environments. I describe herein a few additional examples, including the first ones from brackish water. In one well documented case, juvenile snooks, Centropomus mexicanus (Centropomidae) join bottom-foraging groups of the superficially similar mojarras, Eucinostomus melanopterus (Gerreidae) and prey on small fishes and crustaceans under such disguise. Two other snook species and two species of groupers (Serranidae), are here suggested as additional instances of aggressive mimicry. Furthermore, I review published examples of aggressive mimicry in fishes and indicate trends in the relationships between the mimics, their feeding tactics, and their putative models. Three large families, Serranidae, Cichlidae, and Blenniidae display most of the examples of aggressive mimicry, serranids being largely represented by the genus Hypoplectrus and blenniids by the tribe Nemophini only. Three major trends are here indicated for aggressive mimics: (1) fish species that feed on prey smaller than themselves tend to mimic and join fish species harmless to their prospective prey; (2) fish species that feed on prey larger than themselves tend to mimic mostly beneficial fish species (cleaners) or, less frequently, join species harmless to their prospective prey; (3) fish species that feed on prey about their own size tend to mimic their prospective prey species, the perfect ‘wolf in a sheep’s clothes’ disguise type. The latter deceit is recorded mostly for scale and fin-feeding freshwater fishes. Introduction An aggressive mimic resembles a beneficial or an otherwise harmless model in which guise the mimic capitalise to approach and prey on its unaware victims (Wickler 1968). Examples of aggressive mimicry among fishes include both freshwater and marine species whose feeding habits vary from taking fin pieces or scales of larger fishes to preying on whole smaller fishes and crustaceans (e.g., Trewavas 1947, Randall & Randall 1960, Sazima 1977, Ormond 1980). ∗ Dedicated to Eugene K. Balon, a lively and open minded ichthyologist, on his retirement from editing Environmental Biol- ogy of Fishes for the last quarter century. The most often cited instance of aggressive mimicry is the blenniid Aspidontus taeniatus, which closely resembles the cleaning labrid Labroides dimidiatus and approach larger unsuspecting fishes biting off pieces of fins and epidermis (e.g., Eibl-Eibesfeldt 1959, Randall & Randall 1960, Kuwamura 1983). Other examples include juvenile or adult carnivo- rous species which mimic, and frequently associate with, planktivorous, micro-carnivorous, or herbivorous fishes (e.g., Randall & Randall 1960, Ormond 1980, Randall 1989, Domeier 1994). I describe herein additional examples of aggres- sive mimicry including the first ones among brack- ish water fishes. I found that juveniles of the snook Centropomus mexicanus (Centropomidae) and the