Metabolism-Body Mass Relationship During the Larval Stage of Fish

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The relationship between metabolism M and body mass W during the larval stage was examined at 20^ﾟC based on M=aW^b, with a porgy Pagrus major.There was a triphasic ontogenetic change in the relationship between oxygen consumption of an intact fish M_<in vivo>(mul・min^<-1>) and body mass W (g). During a very early stage (weight 0.00020-0.00025g ; 0-6days old after hatch), corresponding to the prelarval stage and with the transitional period to the postlarval stage, there was no substantial change in body mass. The mass-specific metabolic rate M_<in vivo>/W(mul・g^<-1>・min^<-1>) showed no clear relationship to body mass as expressed by the equation M_<in vivo>/W=4.86+1.47・D, where D is age in days. During the postlarval stage (0.00031-0.005g ; 8-25days old), M_<in vivo>/W remained almost constant independent of body mass following the expression M_<in vivo>=12.5W^<0.949>. During the juvenile and later stages (0.005-270g ; 25-530 days old), M_<in vivo>/W decreased with increasing body mass following the expression M_<in vivo>=6.3W^<0.821>. It was considered, therefore, that the decrease in mass-specific metabolic rate with increasing body mass is not a universal phenomenon.Oxygen consumption in vitro of an individual fish M_<in vitro>, which was determined in chopped preparation of a whole body, showed the same ontogenetic changes against body mass as M_<in vivo>. Therefore, scale effect on the metabolism was considered to exist in vitro as well as in vivo.Relative mass of the head, trunk and viscera was almost constant independent of body mass during the postlarval stage. Mass-specificrate of tissue metabolism QO_2 of them decreased only slightly with increasing body mass during this stage. Based on relative growth and QO_2, the b-valuewas calculated to be 0.94, which was close to the value in vivo during the postlarval stage, 0.949.