Effects Of Exchange Area And Metabolic Level On Allometric Exponent Of Metabolic Rate Of Black Carp

In this study,the black carp（Mylopharyngoden piceus）were used as experimental animal and the body mass（M）scaling of resting metabolic rate（RMR）,maximum metabolic rate（MMR）,ventilation frequency（VF）,oxygen consumption per frequency（OCPV）,gill surface area（GSA）,body surface area（BSA）,total surface area（TSA）,total mass of active organs(M_Active),total mass of inactive organs(M_Inactive),metabolic rate of red blood cell(MR_RBC,MR_SRBC),red blood cell area(S_RBC),red blood cells count（RBCC）,hemoglobin concentration（Hb）were analyzed.The effects of exchange area and metabolic level on the allometric exponent were analyzed under different temperature.The results were as follows:1.RMR and MMR of the black carp were positively correlated with M by powers of 0.833（b_R）and 0.775（b _M）,respectively.The b_R value was significantly larger than 3/4（t=2.936,p=0.007）,while b_M was not significantly different from 3/4（t=0.592,p=0.559）.Both b_R（t=5.950,p<0.0001）and b_M（t=5.277,p<0.0001）were significantly less than 1.There were no significant difference between b_R and b_M（F=1.264,p=0.266）.2.There were not obvious correlations between M and the blood parameters,including S_RBC（r²=0.0045,p=0.726）,RBCC（r²=0.0454,p=0.484）,and Hb（r²=0.0554,p=0.221）.3.The scaling exponent of M_Inactive was 1.005 and was significantly larger than 1（t=2.568,p=0.016）.The scaling exponent of M_Activective was 0.953 and was not significantly different from 1（t=1.949,p=0.061）.In addition,RMR was negatively correlated with M_Inactive.4.The surface area parameters of black carp were positively correlated with M.In the fish post MMR determination,TSA（r²=0.978,p<0.001）,GSA（r²=0.968,p<0.001）,and BSA（r²=0.989,p<0.001）scaled with M by exponents of 0.814(b_TSA),0.867(b_GSA),and 0.677(b_BSA),respectively.In the fish under resting status,TSA（r²=0.986,p<0.001）,GSA（r²=0.979,p<0.001）,and BSA（r²=0.995,p<0.001）scaled with M by exponents of 0.840(b_TSA),0.897(b_GSA),and 0.684(b_BSA),respectively.Using M as the covariable,no significant difference was found between b_GSA and b_R.5.M was positively correlated with VF and OCPV,and scalling exponents were 0.080(b_VF) and 0.771(b_OCPV),respectively.Using M as the covariable,b_R was positively correlated with b_VF（F=490.543,p<0.0001）and b_OCPV（F=5.517,p=0.021）.6.RMR was positively correlated with M and b_R were 0.748 and 0.824,at 10 and 25℃,respectively.There was no significant difference between b_R values between temperatures,while the RMR at 25℃was significantly higher than the RMR at 10℃.7.MR_RBC and MR_SRBC were positively correlated with M,and b_MRRBC and b_MRSRBC values were 0.401,0.358 at 25℃.However,MR_RBC and MR_SRBC did not correlate with M at 10℃.8.The scaling exponent of GSA was 0.802(b_GSA)at both two temperatures.GSA was larger at 10℃than at 25℃（F=35.908,p<0.0001）using M as a covariate.Partial correlation analysis showed that GSA and RMR were positively correlated at both temperatures （10℃:r=0.935,p<0.0001;25℃,r=0.970,p<0.0001）.Gill lamellar area at 10℃,was significantly higher than that 25℃（F=52.463,p<0.0001）using M as the covariate.However,the total number of gill filamentswas significantly larger at 25℃ than at 10℃（F=4.278,p=0.043）.Other parameters showed no significant difference.9.VF decreased with the increasing M,and b_VF was 0.440 at 25℃.However,VF increased with the increasing M,and b_VF was 0.257 at 10℃.OCPV increased with the increasing M at both temperatures.b_OCPV were 1.229 and 0.489 at 25 and 10℃,respectively.Controlling the influence of M,the partial correlation analysis showed that VF correlated with RMR negatively（r=0.715,p<0.0001）at 25℃,but positively（r=0.976,p<0.0001）at 10℃.OCPV and RMR were positively correlated at both temperatures（25℃:r=0.419,p<0.0001;10℃:r=0.649,p<0.0001）.The conclusions were as follows:1.The proportion of inactive organs increases weakly with the increasing M.M_Inactive negatively correlated with RMR with small r²,suggesting that the metabolic allometry of this fish could only be partially explained by the size changes in organ,and may also be involved with changes in other characteristics of organs,such as the metabolic level of organs.2.There was no significant difference between b_R and b_GSA in the black carp,suggesting that mass scaling of RMR might be limited by the GSA,but not the BSA proposed by the surface area theory.The GSA is mainly determined by the area of the secondary lamellaes.3.b_R showed no significant difference between temperatures,different to the prediction of the metabolic-level boundaries hypothesis.S_RBC only increases slightly with the increasing M at 10℃,but keep unchanged at 25℃.However,the b_R shared same value of 0.72 at both temperatures.The results are different to the predictions that b_R should be close to 1,according to the cell metabolism hypothesis.4.The RMR of black carp increased with the increasing temperature,but there was no significant difference between b _GSA and b_R,which is caused by that the VF speeds up and compensates the oxygen demand.Metabolic level was higher,but the S_RBC was smaller at 25℃.The interaction of the two factors could induce no significant difference in b_R between temperatures and is consistanted with the surface area-metabolic demand hypothesis.Acturally,the b_R-S formula derived from this hypothesis can effectively predict the b_R value from S of black carp.