FISH and FISHERIES, 2003, 4, 289^347 Taste preferences in ®sh Alexander O Kasumyan1 & Kjell B DÖving2 1Department of Ichthyology,Faculty of Biology,Moscow State University,119992 Moscow,Russia; 2Department of Biology, University of Oslo, N-0136 Oslo, Norway Abstract Correspondence: The ¢sh gustatory system provides the ¢nal sensory evaluation in the feeding process. Alexander O Unlike other vertebrates, the gustatory system in ¢sh may be divided into two distinct Kasumyan, Department of subsystems, oral and extraoral, both of them mediating behavioural responses to food Ichthyology,Faculty items brought incontact withthe ¢sh.The abundance of taste buds is anotherpeculiarity of Biology,Moscow of the ¢sh gustatory system. For many years, morphological and electrophysiological State University, techniques dominated the studies of the ¢sh gustatory system, and systematic investiga- 119992 Moscow, tions of ¢sh taste preferences have only been performed during the last 10 years. In the Russia E-mail: present review,basic principles in the taste preferences of ¢sh are formulated. Categories alex_kasumyan@ or types of taste substances are de¢ned in accordance with their e¡ects on ¢sh feeding mail.ru behaviour and further mediation by the oral or extraoral taste systems (incitants, sup- pressants, stimulants, deterrents, enhancers and indi¡erent substances). Information Received17July 2002 on taste preferences to di¡erent types of substances including classical taste substances, Accepted3April 2003 free amino acids, betaine, nucleotides, nucleosides, amines, sugars and other hydrocar- bons, organic acids, alcohols and aldehydes, and their mixtures, is summarised. The threshold concentrations for taste substances are discussed, and the relationship between ¢sh taste preferences with ¢sh systematic positionand ¢sh ecology is evaluated. Fish taste preferences are highly species-speci¢c, and the di¡erences among ¢sh species are apparent when comparing the width and composition of spectra for both the stimu- lants and the deterrents.What is evident is that there is a strong similarity inthe tastepre- ferences between geographically isolated ¢sh populations of the same species, and that taste preferences are similar in males and females, although at the individual level, it may vary dramatically among conspeci¢cs.What is noteworthy is that taste responses are more stable and invariable for highly palatable substances than for substances with a low level of palatability.Taste preferences as a function of pH is analysed.There is a good correspondence between development of the gustatory system in ¢sh ontogeny and its ability to discriminate taste properties of food items. There is also a correspondence between oral and extraoral taste preferences for a given species;however,there is no cor- relationbetween smelland taste preferences.Taste preferences in ¢sh show low plasticity (in relation to the diet), appear to be determined genetically and seem to be patroclinous. Fish feeding motivation and various environmental factors like water temperature and pollutants such as heavy metals and low pH water may shift ¢sh taste preferences. Com- parisons between bioassay and electrophysiological data show that palatability is not synonymous with excitability inthegustatorysystem.The chemical nature of stimulants and deterrents in various hydrobionts is outlined. The signi¢cance of basic knowledge in ¢sh taste preferences for aquaculture and ¢sheries is emphasised. Key words feeding behaviour, ¢sh, food intake, gustatory system, taste preferences, taste stimulants # 2003 Blackwell Publishing Ltd 289 Taste preferences Alexander O Kasumyan & Kjell B DÖving Introduction 291 The gustatory system in ®sh 292 Feeding behaviours mediated by the gustatory system 297 Classi®cation of taste substances 298 Methods in studies of ®sh taste preferences 299 Taste preferences to different types of substances 300 Classical taste substances 300 Free amino acids 301 Betaine 306 Nucleotides and nucleosides 306 Amines 307 Sugars and other hydrocarbons 307 Organic acids 308 Alcohols and aldehydes 308 Other types of substances 309 Mixtures 309 Thresholds 310 Speci®city of taste preferences 313 Species speci¢city 313 Population speci¢city 315 Speci¢cityamong conspeci¢cs 315 Speci¢city between sexes 317 Genetics of taste preferences 318 Ontogeny of taste preferences 319 Ecology of taste preferences 320 Internalfactors effecting taste preferences 322 Feeding experience 322 Feeding motivation 323 Environmentalfactors effecting taste preferences 323 Temperature 323 Water pollutants 324 Low pH water 325 Taste preferences as a function of pH 326 Chemicalnature of stimulantsin ®sh food organisms 327 Relation between oral and extraoral taste preferences 329 Correlation between bioassay and electrophysiological data 330 Correlation between smell and taste preferences 331 Naturaldeterrents 332 Application in aquaculture and ®sheries 334 Epilogue 335 Acknowledgements 336 References 336 290 # 2003 Blackwell Publishing Ltd, F I S H and F I S H E R I E S, 4,289^347 Taste preferences Alexander O Kasumyan & Kjell B DÖving also participate in the consummatory phase in ¢sh. Introduction The sense of touch or mechanoreception is function- The aim of the present review is to provide a basis for ally and structurally connected to the gustatory sys- understanding ¢sh feeding behaviour through an tem (Kanwal and Caprio 1988;Hayama and Caprio examination of the taste preference ¢sh have for dif- 1989, 1990). It has been noted, for example, that an ferent foods and the single chemical components of increased hardness or presence of acute outgrowths the food. and spines on the external integument of the food Feeding in ¢sh, as in other groups of animals, is an organisms results in a decrease in consumption of important function of life, and is a result of processes such organisms by ¢sh (Hunter 1980;Lemm 1983; that are associated with searching, aiming, accept- Stradmeyer et al.1988;Stradmeyer 1989). The number ing, seizing, oral processing and evaluation of the of such examples is limited, and thus may indicate quality of food objects. Swallowing, digestion, an auxiliary role of mechanoreception in ¢sh feeding absorption and assimilation follow these processes. behaviour. Additionally, althougth there are numer- The success of these tasks, directly related to the ous solitary chemosensory cells covering the oral satisfaction of energy requirements, is responsible cavity of ¢sh (Whitear 1992;Whitear and Moate for the rate of growth, maturation and fecundity of 1994), there are few data on the functional properties ¢sh, their social status, migratory activity, life strat- of this common chemical sense (Silver 1987;Silver egy and their resistance to the impact of unfavour- and Finger1991;Kotrschal1996), and we do not know able factors. what role this chemosensory system plays in the oral Many sensory systems contribute to ¢sh feeding evaluation of prey quality.Furthermore, there are no behaviour, but their role and signi¢cance may pro- data to indicate an obvious role of the common che- foundly di¡er at di¡erent phases of the feeding beha- mical sense in the ¢nal phase of ¢sh feeding beha- viour. The consummatory phase of the feeding viour (Kotrschal1991,1992,1995;Whitear1992). behaviour starts with the awareness of a food object Studies of the gustatory system of ¢sh began in the and terminates with either swallowing or rejection. 19th century, and for many years, morphological The various sensorycues involved inthese tasks vary, techniques dominated this area of research. In the but what determines the palatability (taste) of a food last decades, electro-physiological methods have object for the ¢sh involves predominantly gustatory come into use to evaluate the properties of the gusta- and some aesthetic qualities. Various mechanosen- tory system. Presently, there are several reviews on soryorgans, and what is termed as a common chemi- the ¢sh gustatory system, focusing on ¢sh taste bud cal sense, can mediate these latter qualities. In many morphology and distribution (Kapoor et al. 1975; instances, a ¢sh rejects a food item after it has been Tucker1983;Jakubowski andWhitear1990;Gomahr taken into the mouth cavity (Bardach et al.1959;Tes- et al. 1992;Reutter 1992;Reutter and Witt 1993), the ter1963;Atema1980;Gerhart et al.1991;Schulte and physiologyof the peripheral taste neurones (Bardach Bakus 1992). Such behaviour demonstrates that an and Atema 1971;Caprio 1982;Tucker 1983;Caprio object that is selected as a food item, based on the 1984;Caprio 1988;Hara 1994a,b), the molecular information given by any of the sensory systems mechanisms of taste receptor transduction (Brand available, is not su¤cient to guarantee its suitability and Bruch 1992) and the organisation of gustatory as food for the ¢sh. The sensory systems in question neural pathways within the central nervous system are olfaction, vision, acoustic, lateral line organ, of ¢sh (Kanwal and Finger1992). extraoral gustatory subsystem or electroreception. Methods for estimation of ¢sh taste preferences This consideration indicates the important control have been nonexistent or at best, primitive, and have functions of receptors located within the ¢sh'smouth not been elaborated until recent times.When study- cavity in evaluating the speci¢c food items. ing taste preferences in ¢sh, it is di¤cult to avoid the The gustatory sensory system provides the ¢nal in£uence of other chemosensory systems and, while evaluation in the feeding process.