Effect Of Exchange Surface Area On Metabolic Scaling In Fishes

Allometric scaling phenomenon of metabolic rate with body mass(M)is one of the basic issues in physiological ecology.Many theories have been proposed to explain metabolic scaling,however a lot of controversy still exists.The ‘exchange surface area-metabolic demand constraints’ hypothesis proposed that metabolism of organisms is constrained by exchange restrictions caused by the ‘surface area and volume ratio’ as well as the demand restrictions caused by metabolic activities.The irrelative importance constrains metabolic scaling.Therefore,grass carp(Ctenopharyngodon idellus),silver carp(Hypophthalmichthys molitrix),bighead carp(Aristichthys nobilis)and common carp(Cyprinus carpio)were used to study the effect of exchange surface area on the metabolic scaling exponents among fish species.Resting metabolic rate(RMR),gill surface area(GSA),body surface area(BSA),total surface area(TSA),ventilation frequency(VF),oxygen consumption per ventilation(OCPV),total gill filament number(TGFN),average gill filament length(AGFL),the average density of gill lamellae(ALD)and the average gill lamellae area(ASLA)were measured in the fish with increasing M.The relationships between exchange area parameters and metabolic scaling were analyzed to verify the applicability of the ‘exchange surface area-metabolic demand constraints’ hypothesis in intraspecific metabolic allometry.Results: 1.RMR of all species were increased with M(p < 0.05).The scaling exponents of RMR(b RMR)for grass carp,silver carp,bighead carp,and common carp were 0.824,0.792,0.829,and 0.793,respectively.2.GSA,BSA,and TSA increased as M increased in all species(p < 0.05).The b GSA of grass carp,silver carp,bighead carp,and common carp were 0.846,0.798,0.853,and 0.873.Residual analysis found that RMR were not constrained by GSA in bighead carp(p = 0.252),but were constrained by GSA in grass carp,silver carp,and common carp(p < 0.05).The b BSA of grass carp,silver carp,bighead carp were 0.686,0.668,0.671,and 0.710,respectively.Residual analysis found that RMR were not constrained by BSA in grass carp(p = 0.738)and silver carp(p = 0.286),but RMR were constrained by BSA in bighead carp and common carp(p < 0.05).The b TSA of grass carp,silver carp,bighead carp,and common carp were 0.793,0.733,0.772,and 0.805,respectively.Residual analysis found that RMR were not constrained by TSA in bighead carp(p = 0.479),but RMR were constrained by TSA in grass carp,silver carp,and common carp(p < 0.05).3.OCPV were positively correlated with M in all species(p < 0.05).The b OCPV of grass carp,silver carp,bighead carp,and common carp were 0.851,0.625,0.726 and 0.729,respectively.VF did not significantly change with increasing M in grass carp(p = 0.463)and common carp(p = 0.137),but VF did significantly change with increasing M in silver carp and bighead carp(p < 0.05).4.TGFN,AGFL,and ASLA increased as M increased(p < 0.05).There was negative correlation between ALD and M in all species(p < 0.05).5.The mass-specific resting metabolic rate(Ms-RMR)did not significantly correlated with b RMR among fish species(p = 0.952).Ms-RMR did not significantly correlated with GSA(p = 0.802),BSA(p = 0.509),TSA(p = 0.657).Ms-RMR were positively correlated with VF(p = 0.009),GSA(p = 0.186),and BSA(p = 0.965),but not with b RMR among fish species.After controlling phylogenetical effects,no correlation was found between GSA and BSA(GSA: p = 0.101;BSA: p = 0.615).TSA did not significantly correlated with b RMR among fish species(p = 0.101),but TSA positively correlated with b RMR when controlling phylogenetical effects(p = 0.015).Either VF(p = 0.798)or OCPV(p = 0.862)did not significantly correlated with b RMR among fish species,even after controlling phylogenetical effects(VF: p = 0.789;OCPV: p = 0.713).Conclusion: 1.Species with larger TSA have larger b RMR within the fishes with closed metabolic level,which supports the ‘exchange surface area-metabolic demand constraints’ hypothesis.2.The results indicate that metabolic level of one species is not affected by its GSA,BSA,and TSA,and the intraspecifical relationship between the metabolic level and TSA varies among species.3.BSA is not proportional to M2/3 in each species,and b RMR is greater than 2/3.Therefore,the ‘body surface area’ hypothesis has inadequate basis,and can not be used effectively to explain the metabolic allometric phenomenon.