Effects Of Temperature And Diel Fluctuation Temperature On The Growth And Energy Budget Of Sea Cucumber Apostichopus Japonicus Selenka

Temperature is one of the most important envriomental factors for aquatic animals and temperature in natural aquatic ecosystem fluctuates diurnally and seasonally. However,the influence of temperature on growth of aquatic animals usually has been conducted under constant temperature regimes and some previous studies showed that the growth of some aquatic animals at fluctuating temperature was different from that under constant temperature.A series of indoor experiments were conducted to investigate the effects of temperature and diel fluctuation temperature on the growth, energy budget and oxygen consumption of the sea cucumber Apostichopus japonicus Selenka.In the present study,we studied the effects of diel fluctuation pattern and the combination effects of ration levels and fluctuating temperature.Based on the results of oxygen consumption and energy budgets of sea cucumber at diel fluctuating temperature,the bioenergetic mechanism for the enhancements in growth of sea cucumber A.japonicus under fluctuating temperature was discussed.The main results were presented as the followings:1.We studied the effects of temperature(16,18,20 and 22℃) and ration(0%, 0.3%,0.6%and 1.4%body weight day^-1) on the growth of juvenile sea cucumber Apostichopus japonicus(mean body weight 5.4±0.1 g) over 35 days.For any given ration,food intake(FI),specific growth rate(SGR) and food conversion efficiency (FCE) decreased with increasing temperature.The relationship among SGR_w(in terms of weight),SGR_e(in terms of energy),temperature(T),and ration(%body weight) could be described by the regression equations:SGR_w= 0.132 - 0.024 T + 0.284 R(r² = 0.724,n = 64),and SGR_e = - 0.014 - 0.030 T + 0.312 R(r² = 0.654,n = 64).These equations show that the minimum and maximum amount of energy required for maintenance occurred at 16℃and at 22℃,respectively.Furthermore,the energy requirements for maintenance at high temperatures exceeded the energy intake.The patterns of energy allocation revealed that energy required for respiration increased with increasing temperature.The aestivation of sea cucumbers in summer might be in response to a shortfall in energy intake with respect to an increase of energy consumed in respiration at high temperature.2.We studied the effects of four patterns of diel temperature fluctuation(A,B,C and D) with different temperatures regimes(15±3℃and 18±3℃) and three constant temperatures(15,18 and 21℃) on growth and energy budget of the juvenile sea cucumber Apostichopus japonicus(with a mean wet body weight of 8.01±1.17 g). Modes of A,B,C and D were designated to simulate the temperature changes of the open ponds in which ground water was used to raise sea cucumbers,indoor aqurium. intertidal pool,and extreme temperature changes in the nature water at some special time in summer,repsectively.Each treatment had five replications and the experiment lasted for 38 days.At the constant temperature treatments,specific growth rate(SGR) and food conversion efficiency(FCE) decreased with temperatures increase(P＜0.05).Among the four patterns of temperature fluctuation,the maximum of values of SGR occurred at pattern C,and the SGR in pattern C sea cucumbers was significantly higher than that of sea cucumbers reared in the corresponding constant temperatures. The enhancement of growth rate in pattern C might be attributed to a higher FCE,and less energy lost in respiration and faces.Therefore,the pattern C might be a good choice to control the temperature of ponds in the large-scale aquaculture of sea cucumber.3.The growth of some aquatic animals at fluctuating temperature was different from that under constant temperature.The sea cucumber Apostichopus japonicus can adapt to some temperature fluctuation mode which is simulating nature temperature cycle. So we studied the effects of five rations(0%,0.3%,0.6%,0.9%and 1.4%body weight day^-1) under diel temperature fluctuation mode with two mean temperatures (15±3℃,18±3℃) on growth and energy budget of juvenile sea cucumber A. japonicus.Three constant temperatures(15℃,18℃and 21℃) were designed as controls.Sea cucumbers,with a mean wet body weight of 8.4±0.1 g(mean±S.D.) were allocated into aquaria randomly.Each treatment had five replications and the experiment lasted for 40 days.At the same ration and constant temperature treatments, specific growth rate(SGR) and food conversion efficiency(FCE) decreased with the increasing of temperatures(P＜0.05).Among the station ration treatment under the fluctuation temperature treatment(15±3℃),SGRw of the sea cucumbers reared was significantly higher than that of sea cucumbers reared in the corresponding constant temperatures(15℃)(P＜0.05).This enhancement of growth rate might be attributed to a higher FCE in the temperature fluctuation mode.The insignificant difference of SGRe between 15±3℃and 15℃may due to the change of the fat content of the sea cucumbers reared under the fluctuation temperature treatments.So in the large-scale culture,a proper temperature fluctuation mode may be a wise choice.4.We studied the effect of temperature fluctuations on the growth and energy budget of three sizes of Apostichopus japonicus Selenka[small size(5.1±0.4) g; medium size(15.7±2.2) g;big size(45.6±4.1) g].One fluctuating temperature(15±3℃) and three constant temperatures(12℃,15℃and 18℃) were designated in the present study.The special growth rates(SGR) of small-sized sea cucumbers were significantly higher than the medium- and large-sized sea cucumbers(p＜0.01).The SGR of small- and medium-sized sea cucumbers raised under the fluctuation temperature 15±3℃were significantly higher than the sea cucumbers raised under the constant temperature of 15℃.This result suggested that the small-size sea cucumbers could well adapt to the fluctuation temperature.The highest food conversion efficiency(FCE) occurred at small-sized under fluctuation temperature 15±3℃and it significantly higher than the same size sea cucumbers under the constant temperature(P＜0.05).With temperature rising,the energy used in respiration of the three sizes of sea cucumber increases steadily and the small-sized sea cucumbers allocated more energy to respiration than the other sizes.5.To investigate the effects of diel temperature fluctuation on metabolism of sea cucumber Apostichopus Japonicus Selenka,oxygen consumption rate(OCR) and ammonia excretion rate(AER) of the sea cucumber were measured at 15±3℃and 15℃.The fluctuation temperature had significant effects on oxygen consumption rate(P＜0.05),and OCR of sea cucumber Apostichopus japonicus increased significantly(P＜0.05) as temperature rose in the first day.In the second day,there was no significant differenet in the daily average OCR among the fluctuation temperature(15±3℃) and the constant temperature(15℃).The ARE of the sea cucumbers shows insignificant difference between the sea cucumbers under the constant temperature(15℃) and the fluctuation temperature(15±3℃).The daily averages of oxygen/nitrogen ratio is decreasing with the treating-time(day) the water fluctuation temperature conducted and the high oxygen/nitrogen ratio(over 10) suggested that fat or saccharide were used as major energy sources.