| The food resources obtained by fish from the environment are converted into available energy after digestion and absorption.It is generally believed that energy is prioritized for maintenance demand.The energy demand of nervous system and sensory organs occupies a high proportion in the energy consumption of fish.In the case of limited available energy,the energy consumption of sensory organs is limited by the proportion of energy distribution of the nervous system to the total energy supply of animals,and there may exist an energy trade-off among sensory organs.Vision function consumes more energy than non-visual functions,and an energy trade-off may exist between the visual and non-visual functions.Studies have found that the cavefish Triplophysa rosa has smaller brain and highly degraded eyes,and then saved visual energy consumption.The energy saved by visual degradation can further alleviate the energy limitation of olfactory function.In addition,the olfactory function is more contribute to behavioral activities related to resource acquisition in dark cave environment,which affectes the limitation of energy distribution for growth,reproduction,and storage.Therefore,the study raised the following questions:How is the olfactory sensitivity of cavefish?How is the interspecies relationship between olfactory sensitivity and metabolic level?How is the relationship between olfactory activity and metabolic energy consumption?This study took T.rosa,Triplophysa bleekeri,Paracobitis variegatus,and Discogobio yunnanensis as the research objects,and the following three experiments were carried out.1.The body mass and individual resting metabolic rate of those fishes were measured to compare the metabolic energy consumption between cavefish and surface fish.2.The activity,exploration,and preference behavioral activities were observed after injecting 0,1.2×10-11,1.2×10-9,1.2×10-7,1.2×10-5,1.2×10-3,and 1.2×10-1 M mixed L-amino acids to test the difference of olfactory sensitivity between cavefish and surface fish and to analyze the interspecific relationship between olfactory sensitivity and metabolic level.3.The individual metabolic rate of the four species of fish was measured after injecting 0,1.2×10-3 and 1.2×10-1 M amino acids.The resting metabolic rate of T.bleekeri was measured before and after plugging nostrils and the behavioral activities were observed after injecting mixed L-amino acids to determine the relationship between olfactory activity and metabolic energy consumption.The main results were as follows:（1）The resting metabolic rates were different among species（F=163.72,p<0.001）.The resting metabolic rate of the T.rosa was lower than that of the T.bleekeri（p<0.001）,H.variegata（p<0.001）,and D.yunnanensis（p<0.001）.The resting metabolic rate of T.rosa,T.bleekeri,H.variegata,and D.yunnanensis were 0.090,0.341,0.282,and 0.378mg O2·h-1,respectively,after correcting body mass.（2）The basic activity,exploration,and preference of T.rosa were higher than those of T.bleekeri,H.variegata,and D.yunnanensis.The active concentration thresholds of T.rosa,T.bleekeri,and H.variegata were 1.2×10-9,1.2×10-1,and 1.2×10-5M;the exploration concentration thresholds were 1.2×10-7,1.2×10-3,and 1.2×10-5M.The concentration designed in this study did not cover the activity and exploration concentration threshold of D.yunnanensis.（3）The olfactory bulb masses were different among species（F=37.149,p<0.001）.The olfactory bulb mass of the T.rosa was significantly samller than that of the T.bleekeri（p<0.001）and D.yunnanensis（p<0.001）,but not H.variegata（p=0.92）.The olfactory bulb mass of T.rosa,T.bleekeri,H.variegata,and D.yunnanensis were 0.42,0.83,0.56,and 1.34 mg,olfactory bulb indexs were 0.01%,0.03%,0.02%,and 0.05%,respectively,after correcting mass.There were significant differences in the brain masses among species（F=112.259,p<0.001）.The brain mass of the T.rosa was significantly samller than that of the T.bleekeri（p=0.001）,H.variegata（p<0.001）,and D.yunnanensis（p<0.001）.The brain masses of T.rosa,T.bleekeri,H.variegata,and D.yunnanensis were18.59,21.86,25.87,and 38.38 mg,brain indexs were 0.67%,0.78%,0.93%,and 1.38%,respectively,when correcting body mass.（4）Plugging the nostril had no significant effects on the resting metabolic rate of T.bleekeri（t=0.062,p=0.95）.The threshold values of activity and exploration concentration of the false-plugged T.bleekeri were 1.2×10-1M;there was no obvious threshold in true-plugged T.bleekeri,there were no significant differences in activity,exploration,and preference parameters after injecting mixed L-amino acids（p>0.05）.There was no significant difference among the individual metabolic rate of the four species of fish after injecting mixed L-amino acids（p>0.05）.We can conclude that the metabolic level of T.rosa was only 69.3%-76.5%of other three surface species,but olfactory sensitivity of T.rosa was 104-106times higher than those of the other three species.It indicates that the metabolic rate of species with stronger olfactory sensitivity is not necessarily high.This may be due to an energy trade-off exists between the visual and olfactory functions of the fish in interspecies.Compared with the visual function,the olfactory function consumes a lower level of energy.In addition,factors such as like sleep time,the size of the nostrils and hypothalamus lead to the strong olfactory function of cave fish,which is conducive to the search for food,spouse,and other behaviors in cave habitats. |
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