| A series of indoor experiments were conducted to investigate the effects of light fluctuations on the molting and growth and of Litopenaeus vannamei. Based on the results and the resrarches of temperature flucyuations, the mechanism for the different characters of L. vannamei under fluctuating light and temperature treatments was discussed. The main results were presented as the followings:1. The effects of light fluctuations on the molting, growth of Litopenaeus vannamei and preliminary researches on its mechanisms1.1 The effect of rhythmic light intensity fluctuation on the molting and growth of Litopenaeus vannamei and its mechanismsThe method of experimental ecology was used to investigate the effect of rhythmic light intensity fluctuation on the molting and growth of Litopenaeus vannamei. Molting, growth performance, feeding and body composition of the shrimps were tested in one constant light intensity (2700 lx) treatment and four rhythmic fluctuating light intensity treatments (2700±600 lx; 2700±1200 lx; 2700±1800 lx; 2700±2400 lx). The initial wet body weight of shrimp was 2.736±0.002 g (mean±S.E.), the period of this experiment was 48 days. The main results were as follows:(1) The weight gain (WG) and the specific growth rate (SGRd) of shrimps in 2700±600 lx,2700±1200 lx and 2700±1800 lx treatments were significantly higher than those in 2700 lx treatment (P< 0.05); the WG in 2700±2400 lx treatment was significantly higher than those in 2700 lx treatment (P<0.05), but SGRd was not (P>0.05). (2) The feed intake (FId) in 2700 ±600 lx,2700±1200 lx and 2700±1800 lx treatments were significantly higher than those in 2700 lx treatment (P<0.05), but 2700±2400 lx treatment was not (P>0.05). The food conversion efficiency (FCEd) in 2700±600 lx treatment was significantly lower than those in 2700 lx treatment (P<0.05), but the other three rhythmic fluctuating light intensity treatments were not (P>0.05). (3) The energy allocation to growth in 2700±1200 lx and 2700±1800 lx were significantly higher than those in 2700 lx treatment (P<0.05) and the energy allocation in respiration in 2700±1200 lx and 2700±1800 lx were significantly lower than those in 2700 lx treatment (P<0.05). (4) There was no significantly difference of molting rate (MF) and energy allocation in exuviate between constant light intensity and four rhythmic fluctuating light intensity treatments (P>0.05). (5) The body composition of the shrimps was significantly affected by the different light treatments (P<0.05). Compared to the constant light intensity treatment, the value of crude lipid decreased because of the effect of the fluctuating light intensity.1.2 The effect of periodic abrupt change in light intensity on the molting and growth of Litopenaeus vannamei and its mechanismsThe molting and growth of Litopenaeus vannamei were tested in one constant light intensity (60 lx) treatment and four periodic abrupt changing light intensity treatments (600-60 lx; 1500-60 lx; 3000-60 lx; 6000-60 lx). The initial body weight of shrimp was 2.733±0.017 g (mean±S.E.), the period of this experiment was 48 days. The main results were as follows:(1) The weight gain (WG) and the specific growth rate (SGRd) in 1500-60 lx and 3000-60 lx treatments were significant higher than those in 60 lx treatment (P<0.05); the WG in 600-60 lx treatment was significantly higher than those in 60 lx treatment (P<0.05), but the SGRd was not (P>0.05). Opposite to what was observed in the 600-60 lx treatment, the WG in 6000-60 lx had no difference from those in 60 lx treatment (P>0.05), but the SGRd in 6000-60 lx treatment was significantly higher than those in 60 lx treatment (P<0.05). (2) There is no significant difference in FId for all regimes (P>0.05), but the FId of shrimps in 1500 -60 lx,3000-60 lx and 6000-60 lx treatments were significant higher than those in 60 lx treatment (P<0.05). (3) The energy allocation in respiration and excretion of shrimps in 1500-60 lx,3000-60 lx and 6000-60 lx treatments were significantly lower than those in 60 lx treatment (P<0.05), the energy allocation in the growth were significantly higher than those in 60 lx treatment (P<0.05). (4) The MF and energy allocation in exuviate in 6000-60 lx treatment were lowest, and significantly lower than those in other treatments (P<0.05), but the MF and energy allocation in exuviate in 1500-60 lx or 3000-60 lx treatment was not significantly different from those in 60 lx treatment (P>0.05). (5) The ash had a positive correlation with the body weight, but the crude protein did not, and the abrupt changing light enhanced the content of crude lipid of shrimps.1.3 The effect of rhythmic light color fluctuation on the growth and molting of Litopenaeus vannamei and its mechanismsThe molting and growth of Litopenaeus vannamei were tested under two kinds of color treatments:three constant light color treatments (yellow light, Y; green light, G; blue light, B) and three rhythmic fluctuating light color treatments (blue light was changed to yellow light, BY; blue light was changed to green light, BG; green light was changed to yellow light, GY). The initial body weight of shrimp was 1.212±0.010 g, the period of this experiment was 45 days. The main results were as follows:(1) The weight gain (WG) and the specific growth rate (SGRd) of shrimp in BG and BY treatments were significantly higher than those in B treatment (P>0.05). The WG in GY treatment was significantly higher than those in B treatment (P>0.05), but the SGRd was not (P>0.05). (2) There is no significant difference in FId for all regimes (P>0.05), the FCEd of shrimps in GY treatment was no significantly different from those in B treatment (P>0.05), but the FCEd of shrimps in BY and BG treatments were significantly higher than those in B treatment (P<0.05). (3) However, the energy allocation in respiration of shrimps in all treatment did not have significant difference (P >0.05), but the energy allocation to excretion of shrimps in BG and BY treatments were significantly lower than those in B treatment (P<0.05), the energy allocation to growth were significantly higher than those in B treatment (P<0.05). (4) The molting rate (MF) and energy allocation in exuviate of shrimps in three rhythmic fluctuating light color treatments were generally higher than that in three constant light color treatments (P<0.05), there was a clear correlation between MF and growth in every regime. (5) The ash of shrimps had a positive correlation with the body weight, but the crude protein did not, and the abrupt changing light enhanced the content of crude lipid of shrimps. The lipid level of shrimps increased with the decrease of moisture level.1.4 The effect of periodic light color fluctuation on the molting and growth of Litopenaeus vannamei and its mechanismsThe method of experimental ecology was used to investigate the effect of periodic light color fluctuation on the molting and growth of Litopenaeus vannamei. Molting and growth performance of the shrimps were tested under two kinds of color treatments: three constant light color treatments (yellow light, Y; green light, G; blue light, B) and three periodic fluctuating light color treatments (blue light was changed to yellow light, BY; blue light was changed to green light, BG; green light was changed to yellow light, GY). The initial body weight of shrimp was 1.212±0.018 g (mean±S.E.), the period of this experiment was 48 days. The main results were as follows:(1) the weight gain (WG) and the specific growth rate (SGRd) of shrimp in BG treatments were highest and significantly higher than those in Y or B treatment (P>0.05). The WG in GY treatment was significantly higher than those in Y or B treatment (P>0.05), but the SGRd was not (P>0.05). (2) There is no significant difference in FId for all regimes (P>0.05), the FCEd of shrimps in GY treatment was no significantly different from those in Y or B treatment (P>0.05), but the FCEd of shrimps in BY and BG treatments were significantly higher than those in Y or B treatment (P<0.05). (3) Although there was no significant difference in energy allocation in respiration under different light color regimes (P>0.05); but the energy allocation in respiration in BG treatment was lower about 4% than those in B treatment, so the energy allocation to growth of shrimps in BG treatment was significantly higher than those in Y or B treatment (P<0.05). (4) The molting rate in GY treatment was highest, but there was no correlation between MF and growth. (5) The ash had a positive correlation with the body weight, but the crude protein did not, and the periodic light color fluctuation decreased the content of crude lipid of shrimps.2. Effects and mechanism of light fluctuations on growth of Litopenaeus vannamei2.1 The variation of LD, PK and LDH of Litopenaeus vannamei in periodic abrupt change in light intensity and constant light intensityFour periodic fluctuation light intensity treatments (600-60 lx,1500-60 lx,3000-60 lx and 6000-60 lx) and five constant light intensity treatments (60 lx,600 lx,1500 lx,3000 lx,6000 lx) were arranged to investigate the effect of periodic abrupt change in light intensity and constant light intensity on the enzymes relating to respiratory metabolism. An alternation of six days high light intensity and two days low light intensity was adopted in the periodic fluctuation light intensity treatment. After two cycles of light intensity periodic fluctuation, sampling five inter-molt stage shrimps in the five constant light intensity treatments to assay the PK activities, the LDH activities and the lactic-acid at 0 h,0.5 h,1 h,3 h,6 h,9 h,12 h,14 h after the light on, respectively; and doing that in four periodic fluctuation light intensity treatments at 0.5 h,1 h,3 h,6 h,12 h,24 h,48 h,72 h,144 h,144.5 h,145 h,147 h,150 h,156 h,168 h, 192 h of the third cycle of light intensity periodic fluctuation, respectively. The main results were as follow:(1) A decrease of total PK and LDH activities was found in periodic fluctuation light intensity treatments, but LD been not; the reason for the phenomenon might be that the efficacy of some enzymes was enhanced in periodic fluctuation light intensity treatments. (2) The fluctuations of enzymes in 600 lx and 1500-60 lx treatments were stable, but those in 6000 lx and 6000-60 lx treatments were acute. (3) The lactic-acid content of 6000-60 lx treatment in the phase of high light was high and this phenomenon was also found in the later stages of high light and the beginning of low light in 600-60 lx. These results might indicate that the shrimp may be in a bad environment. (4) The LDH fluctuation when the light changed from high intensity to low intensity was more acute than those when the light changed from low intensity to high intensity. This may due to the difference types of shrimps acclimate to different light intensities and the longer time of high light intensity in our experiment. The results suggested that the suitable periodic abrupt changing light intensity enhanced the effectiveness of the enzyme in shrimps and its fluctuation of enzyme was stable, so the growth of shrimps was better.2.2 The variations of GLU, LD, HK and PKof Litopenaeus vannamei under a rhythmic fluctuating color light and two constant color lightsA rhythmic fluctuating light color treatment (Blue light was changed to green light, BG) and two constant light color treatments (green light, G; blue light, B) were selected from the last experiment to investigate the effect of rhythmic fluctuations in light color on the enzymes relating to respiratory metabolism. Sampling five inter-molt stage shrimps to assay the hemolymph glucose, lactic-acid, the HK and PK activities of hepatopancreas at 7:00,9:00,13:00,14:00,16:00,20:00 on the following days:the first day, third day, fifths day, tenth day, twentieth day and fortieth day of the experiment, respectively. The main results were as follow:(1) The hemolymph glucose content had a small increase after the light on, but the hemolymph lactic-acid content did not. The HK activities of shrimps in B and G treatments decreased after switching on the light, but those in BG treatment increased. And the PK activities in all treatment did not have an obvious change. (2) A significant effect of rhythmic fluctuating light color on glucose, lactic-acid, HK and PK activities was found in the beginning of the experiment, but this effect disappear gradually when the experiment went on. (3) The fluctuations of HK and PK activities of shrimps in B treatment were acute, and the time of HK and PK activities became stable was late; but those in G treatment was comparatively stable.3. Effects and mechanism of temperature fluctuations on growth of Litopenaeus vannamei 3.1 The effects of cyclical temperature changes on growth and physiological status of Litopenaeus vannameiThe purpose of this study was to investigate the growth and physiological status of Litopenaeus vannamei subjected to one constant temperature (25℃) and four cyclical temperature change regimes (25℃±1℃,25℃±2℃,25℃±3℃and 25℃±4℃). The growth rates of shrimp at 25℃±2℃or 25℃±3℃were significantly higher than that at a constant temperature of 25℃. On the other hand, the growth rate in 25℃±4℃regime was significantly lower than those in other regimes. The daily feed intake rate of shrimp at 25℃±4℃was the lowest and the food conversion efficiency was also significantly lower than those at 25℃±2℃and 25℃±3℃, respectively. The food conversion efficiency at 25℃±2℃or 25℃±3℃was significantly higher than those in other regimes. Thus, it can be inferred that the growth enhancement in the test shrimp at the suitable diel fluctuating temperatures was due to high food conversion efficiency. Studies of the physiological parameters showed that at 25℃±4℃, the hemolymph glucose content of the test shrimp was the lowest, while the activity of PK in hepatopancreas was the highest, which indicated that the test shrimp at 25℃±4℃was in a stressed condition. The hemolymph glucose content of the test shrimp at 25℃±3℃was the highest and the activity of HK in hepatopancreas was the lowest. These results indicated that the test shrimps at 25℃±3℃were not in a stressed condition. Compared with the constant temperature regime, the expression of HSP70 in any of the four cyclical temperature change regimes was not significantly increased. The reason for this might be that the fluctuation amplitude of±4℃did not induce the increased expression of HSP70.3.2. The variations of enzymes involved glycolysis and HSP70 of Litopenaeus vannamei during the temperature cyclical changeThe rhythmic fluctuations of hemolymph glucose content, HK and PK activities in hepatopancreas and HSP70 expression in Litopenaeus vannamei were measured under one constant temperature (25℃) and four cyclical temperature change regimes (25℃±1℃,25℃±2℃,25℃±3℃and 25℃±4℃). The main results were as follows: a day/night rhythmicity was found in the rhythmic fluctuations of hemolymph glucose content and HSP70 expression under 25℃, but the rhythmicity disappeared gradually with the increased fluctuation amplitude of temperature. The PK activities varied gently under 25℃. Due to the increase of temperature fluctuation amplitude, the fluctuation of PK activities became acute, especially in 25℃±4℃regime. Because of the effect of glucose flux and glycolysis, the fluctuation of HK activity became stable with the increased fluctuation amplitude of temperature.
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