Linkage between metabolic ontogeny and cannibalism in perch-like fish and their derivatives

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The relationship between resting metabolic rate M and body mass W of animals is expressed by an allometric formula M=aW^b, where ‘a' is mass coefficient and ‘b' mass exponent. Mass exponent is smaller than unity, because mass-specific metabolic rate M/W usually decreases with increasing body mass. This phenomenon is well known interspecifically (among species) as well as intraspecifically (within a species). The ontogeny of metabolism (intraspecific change of M/W with growth) is a complex process in which several phases can be distinguished. However, the precise nature and the biological meaning of the ontogeny of metabolism have not been established in teleost fishes, because of very small and fragile nature of larvae and juveniles. Here we show that M/W of a puffer fish Takifugu rublipes decreases with increasing body mass, but it increases abruptly accompanying a severe cannibalism when getting to a certain growth stage. We found in respirometry that the puffer ranging 0.0008-3g in wet body mass had four independent allometric formulae M/W=a_iW^<b-1>, in which the mass coefficient ‘a_i' increased three times abruptly or in a short period at around 0.002, 0.01 and 0.1g, although keeping a constant mass exponent (b=0.82). There were three peaks of cannibalism corresponding to these increases of ‘a_i'. Increases of ‘a_i' with increasing body mass or with growth are unusual, but it would be found in various teleost fishes, if careful respirometry were taken. Similar phenomena to the puffer fish were observed in a flounder Paralichthys olivaceus and a mackerel Scomber japonicus. In the natural condition, these phenomena imply that individuals with growing ability more rapidly are assured of higher survival to reduce predatory risk.