| Fish need allocate the obtained energy to maintenance,growth,reproduction,and storage,ensuring the normal progress of multiple physiological processes and behavioral activities.The energy balance between the various demand components is one of the important issues of fish physiology and ecology.When available energy is limited,more energy will be allocated to the demand components other than maintenance demand.Generally,energy is allocated to maintenance firstly,and then to growth,reproduction,and storage in turn when maintenance demand is met.In the maintenance,the energy consumption of nervous system and sensory function are high.Among the sensory function,the energy consumption of vision is the highest.The energy demand of sensory function is limited by the energy distribution within the nervous system,which may comform an energy trade-off between visual and non-visual sensations.Triplophysa rosa is a typical cavefish with degenerated eyes and midbrain,extremely low metabolism,living in a dark cave,potentially limited food resources,and limited available energy.The T.bleekeri,Homatula variegata,Discogobio yunnanensis,and Belligobio nummifer are surface species,living in rivers with relatively abundant resources.This study selected the above five fish species as the research objects.And the following two experiments were carried out.The first experiment was that the metabolic rate of the individual and active organs(brain,heart,liver,eye,and olfactory bulb)of these five species were measured to exam whether there was a trade-off between visual and olfactory energy consumption intra-and inter-species.The second experiment was that the chemical composition of the fish and the energy content of T.rosa and T.bleekeri were determined to exam whether there was a trade-off between the metabolic cosumption and energy storage intra-and inter-species.The above work provides basic data for the study of evolutionary physiology and energetics of fish in special environment.The main results are as follows:1.There were significant differences in the resting metabolic rate among species(F = 82.056,p < 0.001).The resting metabolic rate of T.rosa was significantly lower than that of T.bleekeri(p < 0.001),H.variegata(p < 0.001),D.yunnanensis(p < 0.001),and B.nummifer(p < 0.001).Correcting to the average body mass of 3.28 g,the resting metabolic rate of T.rosa,T.bleekeri,H.variegata,D.yunnanensis and B.nummifer were 0.110,0.393,0.328,0.430 and 0.404 mg O2·h-1,respectively.2.There were significant differences in total organ metabolic rate among species(F = 8.496,p < 0.001).The total organ metabolic rate of T.rosa was lower than that of D.yunnanensis(p = 0.002)and B.nummifer(p = 0.003),but higher than T.bleekeri(p = 0.029).There was no difference between T.rosa and H.variegata(p = 0.770).The metabolic rate of brain of T.rosa was lower than that of B.nummifer(p = 0.017),but not in the metabolic rate of brain among T.bleekeri,H.variegata,and D.yunnanensis(p > 0.05).The brain mass of T.rosa was lower than that of H.variegata(p < 0.001),D.yunnanensis(p < 0.001),and B.nummifer(p < 0.001),but not between T.rosa with T.bleekeri(p = 0.059).The liver mass of T.rosa was lower than that of T.bleekeri(p < 0.001),and there was no significant difference among H.variegata,D.yunnanensis,B.nummifer,and T.rosa(p > 0.05).The heart mass of T.rosa was lower than that of T.bleekeri(p < 0.001),H.variegata(p < 0.001),D.yunnanensis(p < 0.001),and B.nummifer(p < 0.001).The olfactory bulb mass of T.rosa was lower than that of T.bleekeri(p < 0.001),H.variegata(p < 0.001),D.yunnanensis(p < 0.001),and B.nummifer(p < 0.001).3.Percentages of the olfactory bulb metabolic rate to the resting metabolic rate of T.rosa,T.bleekeri,H.variegata,D.yunnanensis,and B.nummifer were 0.24%,0.07%,0.09%,0.10%,and 0.08%,respectively,while percentages of the eye metabolic rate to the resting metabolic rate of T.rosa,T.bleekeri,H.variegata,D.yunnanensis,and B.nummifer were 0,0.30%,0.41%,0.88%,and 0.91%,respectively.There was no significant correlation between the eye metabolic rate and the olfactory bulb metabolic rate within species in T.bleekeri(r = 0.242,p = 0.501),H.variegata(r = 0.132,p = 0.716),D.yunnanensis(r =-0.588,p = 0.057),and B.nummifer(r = 0.146,p = 0.707).The T.rosa has degenerated eyes and higher percentages of the olfactory bulb metabolic rate to the resting metabolic rate than those of surface fishes(p < 0.05).4.The total nerve metabolic rate negatively correlated with the liver metabolic rate of T.rosa(r2 = 0.415,p = 0.003).There was no correlation between the total nerve metabolic rate and the liver metabolic rate of the other four species(p > 0.05).The total nerve metabolic rate positively correlated with the heart metabolic rate of T.rosa(r2 = 0.226,p = 0.046)and D.yunnanensis(r2 = 0.465,p = 0.015).There was no correlation between the total nerve metabolic rate and the heart metabolic rate of the other three species(p > 0.05).5.Body water content was negatively correlated with fat content(r2 = 0.873,p < 0.001)and energy content(r2 = 0.949,p < 0.001),with no significant correlation with protein content(r2 = 0.020,p = 0.660)and ash content(r2 = 0.106,p = 0.302)of T.rosa.5.Body water content was negatively correlated with fat content(r2 = 0.675,p < 0.001),protein content(r2 = 0.410,p = 0.001)and energy content(r2 = 0.844,p < 0.001),while positively with ash content(r2 = 0.213,p = 0.023)of T.bleekeri.6.Body protein content(F = 135.298,p < 0.001)and ash content(F = 22.311,p < 0.001)of T.rosa were lower than that of T.bleekeri.The body fat content of T.rosa was higher than that of T.bleekeri(F = 59.149,p < 0.001).The body water content of T.rosa was not different with that of T.bleekeri(F = 3.576,p = 0.067).The body energy content of T.rosa was higher than that of T.bleekeri(F = 30.486,p < 0.001).The conclusions of this study were as follows:1.Compared to surface fishes,the cavefish T.rosa has lower resting metabolic rate and smaller active organs,but similar active organs metabolic rate.Therefore,the difference of active organs cannot explain the difference of metabolism between cavefish and surface fishes.In addition,although the brain of T.rosa was small,its brain metabolic rate of was not low.Therefoer,the low resting metabolic rate of T.rosa should not be related to the degeneration of visual center.2.Compared to surface fishes,the cavefish T.rosa has degenerated vision and stronger olfactory function,but smaller olfactory bulb and higher percentage of olfactory bulb metabolic rate to resting metabolic rate.It indicates that the difference in olfactory function among species does not depend on the olfactory bulb size and there is a tradeoff between visual energy consumption and olfactory energy consumption.3.There was a negative correlation between the total nerve metabolic rate and the liver metabolic rate in T.rosa,but not in the other four surface fishes.There was a positive correlation between the total nerve metabolic rate and the heart metabolic rate of T.rosa and D.yunnanensis,but not in the other three surface fishes.In this study,energy trade-off between the nerve tissue and the liver appears only in T.rosa.4.Compared to the surface fish T.bleekeri,the cavefish T.rosa has lower metabolic level,higher fat content and energy content,which may be beneficial to improve the adaptability of T.rosa to cave environment.It also indicates that there is a trade-off between metabolic consumption and energy storage among species. |
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