Studies On Respiratory Metabolism Of Large Size Derbio(trachinotus Ovatus L.)

Respiratory metabolism of fishes,affected by water quality parameters,is the important characterization of physiological activity and metabolism,such as ingestion,activity,growth and development and so on.It's very important to study the relationship between respiratory metabolism and water quality parameters for guiding the actual aquaculture.Derbio?Trachinotus ovatus,L.?is a rare edible fish with delicious meat and high nutritional value.It has become one of the main marine aquaculture species in South China,with a fast growth speed and ever-increasing culture areas and production in recent years.This study aimed to elucidate the effects of temperature,salinity,feeding,and acute ammonia and nitrite exposure on the respiratory metabolism and some physiological and biochemical responses in large size derbio?average body mass,74.73⁹6.35g?by AQUARE·SP computerized intermittent flow respirometry under laboratory conditions.Main directly detected indicators were asphyxia point,consumption oxygen rate?MO₂?,ammonia excretion rate?R_N?,liver glycogen?LG?,liver lactic acid?LD?,plasma ammonia?PA?,hemoglobin?Hb?and methaemoglobin?MetHb?.The changes of respiratory metabolism in derbio were discussed.The adaptation and the adapted mechanism to the above factors in derbio were preliminary stated.The major results are as follows:1.Effect of temperature on the respiratory metabolism in derbio The MO₂,R_N,metabolic rate(R_EO),excretion rate(R_EN)and O:N ratio of derbio all increased significantly as temperature increasing from 19 ^oC to 33 ^oC,while ammonia quotient?AQ?and protein energy proportion?PEP?declined as temperature increasing from 19 ^oC to 28 ^oC and kept steady at 28 ^oC and 33 ^oC.The temperature quotient(Q₁₀)reached minimum at 1.59 as temperature increasing from 28 ^oC to 33 ^oC.LG declined significantly and LD decreased as temperature increasing.2.Effect of salinity on the respiratory metabolism in derbio In the range of salinity from 15‰to 30‰,MO₂,R_N,R_EO,R_EN,AQ and PEP of derbio all changed as a concave parabola as the salinity increasing,and all reached its minimum in the salinity range between 20‰to 25‰,but the value of O:N ratio was changed opposite the above parameters.And LG and LD changed not obviously.3.Effects of temperature and salinity on asphyxia point in derbio The suffocation time and asphyxia point of derbio were measured at three temperatures?23,27,31??over a range of salinities?20,25,30‰?.Results showed:at the same salinity level,with increasing temperature,suffocation time declined,while the asphyxia point changed opposite;at the same temperature level,except for the suffocation time and asphyxia point between group?23?,25‰?and group?23?,30‰?and the asphyxia point between group?31?,25‰?and group?31?,30‰?were significantly different,there was no significant difference of suffocation time and asphyxia point between the other groups.4.Effect of temperature on the specific dynamic action?SDA?in post-feeding derbio At 3 temperatures?19,23,27??,postprandial MO₂,R_N,AQ and PEP of derbio were significantly higher than pre-feeding,and the PEP of energy expenditure for SDA in postprandial metabolism(PEP_SDA)accounted for 74.64%,71.34%and 68.83%respectively,with a significantly decline at 27?.With increasing temperature,the standard metabolic rate?SMR?,the standard ammonia excretion rate?STR?,the peak of MO₂ and R_N(P_MO2,P_RN)were significantly increased,while the peak time of MO₂ and R_N?M_T,R_T?,the duration of MO₂ and R_N(D_MO2,D_RN)shortened significantly and all obtained minimum at 27?.At the above temperatures,MO₂ and R_N rose to peak at 8.12,6.42,4.49 h and 5.10,3.80,2.69 h,and recovered to SMR or STR plus 1 S.E.M.at 39.05,29.81,21.12 h and 20.25,19.18,15.66 h post-feeding respectively.Both factorial postprandial MO₂ or R_N scope(F_MO2,F_RN)and the total MO₂ or R_N SDA magnitude(M_MO2,M_RN)changed not obviously.The average F_MO2,F_RN,M_MO2and M_RNwere 2.18,7.19,84.82 mgO₂/g and 8.71 mg TAN/g respectively.5.Effect of ammonia exposure on respiratory metabolism in derbio The total ammonia-nitrogen?TAN?concentration in T₀?control?,T₁,T₂ and T₃treatments were 0.08,1.07,1.98 and 3.07 mg/L?0.00,0.05,0.09 and 0.15mg/L un-ionized ammonia-nitrogen?NH₃-N??,respectively.After acute ammonia exposed for 24 h,the parameters of respiratory physiology and metabolism were measured.The results indicated that,with the increase of TAN concentration,MO₂ and R_EOimproved to a steady level,while PA and O:N ratio kept rising.All of the above respiratory metabolism parameters of T₂ and T₃ treatments were significantly exceeding T₀ treatment.LG significantly declined in three ammonia exposure treatment.R_N,AQ and PEP showed a downtrend when TAN concentration exceeding 1.07mg/L,and reduced significantly in T₂ and T₃ treatments.No significant change was found in LD.Correlation and regression analysis showed a high correlation between NH₃-N concentration and all of the above parameters but not for LD.6.Effect of nitrite exposure on respiratory metabolism in derbio Derbio were immersed in the four groups N₀?control?,N₁,N₂ and N₃ for 24 h,whose average nitrite nitrogen?NO₂^--N?concentration were 0.03,1.47,3.62 and 5.99mg/L,respectively.Acute nitrite exposure significantly reduced Hb and LG than control,but opposite performance placed on MetHb.MO₂,R_EO,R_N,AQ and PEP of N₂ and N₃treatments significantly decreased than control,while LD and O:N ratio increased significantly.