Effects And Mechanism Of Light And Artificial Shelter On Behavior And Growth Of Sea Cucumber, Apostichopus Japonicus

1. Eight light-intensity treatments (natural light, continuous darkness, and 15 lx, 30 lx, 60 lx, 125 lx, 250 lx, and 500 lx under LD 12:12 cycle) were used to investigate the effects of light intensity on the daily activity of 30.27±3.08 g sea cucumber Apostichopus japonicus. Cyclic nocturnal activity patterns of behaviour were observed under natural light cycles (with 73.85% kept hidden at day and 58.64% became active at night under the equivalent LD 13:11 cycle), which were also observed at different light intensities in the range 15 lx to 500 lx under LD 12:12 cycle. And an ongoing nocturnal cycle persisted in DD cycle for up to 8 days, but longer feeding time and less marked rhythm occurred at continuous darkness. A. japonicus moved to shelter around sunrise (5:00-6:00 h) and emerged close to sunset (19:00-20:00 h). The relationship between light intensity (I) and the distribution rate (DR) of A. japonicus exposed to light under different light intensity treatments could be described by the cubic equation as follow: lgDR=0.351[lg(I+6)]3-1.922[lg(I+6)]2+ 2.751lg(I+6)+0.557 (0≤I≤500 lx) (F=804.05, P=0.000, R2=0.993). The equation showed that under poor light conditions (I<5.18 lx), the daily activity rhythm of A. japonicus was governed by an innate biological clock and the effect of light intensity was not significant among different treatments. And more individuals tended to retreat to shelters (from 56.04% to 91.83%) with the increase of light intensity within the weak light condition (from 5.18 lx to 278 lx). However, the daily behaviors of A. japonicus were influenced under strong light conditions (>278 lx). Less than 8.17% individuals kept actively feeding and the proportion was not decreased with the increase of light intensity.2. Ten photoperiod treatments (LD 0:24 cycle (DD cycle), LD 3:21 cycle, LD 6:18 cycle, LD 9:15 cycle, LD 12:12 cycle, LD 15:9 cycle, LD 18:6 cycle, LD 21:3 cycle and LD 24:0 cycle under 500 lx) were used to investigate the effects of photoperiod on the daily activity of 29.77±0.21 g sea cucumber Apostichopus japonicus. Cyclic nocturnal activity patterns of A. japonicus were observed under all photoperiods. But the juveniles spent more or less time moving and feeding with the less marked ongoing nocturnal activity cycle under continuous darkness (DD cycle) or continuous light (LD 24:0 cycle) than natural light cycle, respectively. And there were shorter sheltering time and longer feeding time under them. There were a sheltering behavior transition and two emerging behavior trasitions of juvenile A. japonicus under 6~12 h L photoperiods in the experiments. The behavior transitions were governed by innate biological clock and induced by the signal of daily light variation.The behaviors of juvenile A. japonicus at"daytime"increased significangtly with the lengthening of"light time"(P<0.05) except LD 3:21 cycle. But there was not significant difference among the mean DR of juvenile A. japonicus per day under LD 6:18 cycle, LD 9:15 cycle, LD 15:9 cycle and LD 12:12 cycle.3. In the present study, the effect of various artificial shelters on shelter selection of juvenile sea cucumber Apostichopus japonicus, was evaluated. The preference of juveniles in the experiments with eight different material artificial shelters was compared and showed that the stone, cement duct, polywoven bag, ceramic tile and PVC (polyvinylchloride) duct attracted significantly more juveniles than low-pressure polyethylene duct, wood block and corrugated board (P<0.05). In addition, the influence of biofilmed shelters which were pre-cultured for 0.5 M (month), 1 M, 1.5 M and 2 M were compared with non-filmed shelters (0 M). The number of juveniles attracted by biofilmed shelters was significantly higher than that without biofilm, as follows: 1.5 M>2 M>1 M>0.5 M>0 M. And the number of juveniles of 1.5 M was significantly higher than the other treatments (P<0.05) except 2 M (P>0.05). The selection of juveniles with six different color shelters was compared, and the green shelters attracted significantly more juveniles than the white shelters (P<0.05).4. Growth performance, energy budget and biochemical composition of juvenile sea cucumber (Apostichopus japonicus) were studied over 56 days under 6 different light intensities, as follows: 0 lx, 100 lx, 500 lx, 1000 lx, 2000 lx and 3000 lx. First, the specific growth rate (SGRw) of juvenile A. japonicus increased with the increase of light intensity and it peaked at light intensity of 2000 lx with 1.50±0.12% (P<0.05), then decreased; SGRw under different light intensities was as follows: 2000 lx>3000 lx>1000 lx>500 lx>0 lx>100 lx. Second, the feed intake (FIw) increased with the increase of light intensity then decreased, and it peaked at 2000 lx (25.10±1.51%, P<0.05). Third, there was not significant difference among the food conversion efficiency (FCEw) under different light intensities (P>0.05). Fourth, the energy budget of A. japonicus was significantly affected by different light intensities (P<0.05). The percentage of energy deposited for growth (G) to energy consumed in food (C) was not significantly affected by light intensity (P>0.05). The percentage of energy lost in feces (F) to C increased and peaked at 2000 lx (56.98±4.25%, P<0.05) then decreased with the increase of light intensity. The percentage of excretion energy and respiration energy to consumption decreased and peaked at 2000 lx (7.49±0.04%, P<0.05; 29.72±4.20%, P<0.05) then increased with the increase of light intensity, respectively. Fifth, the body content of crude protein and crude lipid decreased with the increase of light intensity (P<0.05). In conclusion, the effects of light intensity on FI and energy budget contributed to the differences among growth and proximate body composition of A. japonicus under different light intensities.5. Growth performance, energy budget and biochemical composition of juvenile sea cucumber (Apostichopus japonicus) were studied over 56 days under 5 different photoperiods, as follows: LD 0:24 cycle (DD cycle), LD 10:14 cyele, LD 12:12 cycle, LD 14:10 cycle and LD 24:0 cycle. First, the specific growth rate (SGRw) of juvenile A. japonicus increased with the lengthening of days and it peaked at LD 14:10 cycle with 1.24±0.04% (P<0.05), then decreased; SGRw under different photoperiods was as follows: LD 14:10 cycle>LD 12:12 cycle>LD 10:14 cycle>DD cycle>LD 24:0 cycle. Second, the feed intake (FIw) increased then decreased with the lengthening of days, and FIw under LD 10:14 cycle, LD 12:12 cycle and LD 14:10cycle was significantly more than DD cycle and LD 24:0 cycle (13.83±0.16%) (P<0.05). Third, photoperiod affected the food conversion efficiency (FCEw) significantly (P<0.05) and FCEw under different photoperiods was as follows: LD 14:10 cycle> LD 12:12 cycle> LD 10:14 cycle>DD cycle>LD 24:0 cycle. Fourth, there were not significant differences among effects of different photoperiods on the percentage of excretion energy and respiration energy to consumption (P>0.05). But the percentage of energy deposited for growth (G) and energy lost in feces (F) to energy consumed in food (C) was affected significantly by photoperiod. G/C under LD 10:14 cycle was significantly more than that DD cycle, and F/C under LD 14:10 cycle was significantly more than DD cycle (P<0.05), respectively. Fifth, body content of crude protein and crude lipid decreased with the lengthening of days then increased, and they peaked at LD 14:10 cycle with 41.10±0.16% and 5.37±0.05% (P<0.05), respectively. In conclusion, the effects of photoperiod on FI, FCE and energy budget contributed to the differences among growth and proximate body composition of juvenile sea cucumber A. japonicus under different photoperiods.6. The growth performance, energy budget and biochemical composition of juvenile sea cucumber (Apostichopus japonicus) were studied over 56 days under 4 light intensities (0 lx, 1000 lx, 2000 lx and 4000 lx) and 4 photoperiods (LD 0:24 cycle (DD cycle), LD 10:14 cycle, LD 14:10 cycle and LD 24:0 cycle). First, the specific growth rate (SGRw) of juvenile A. japonicus was significantly affected by light intensity, photoperiod and the relationship between them (FP=35.019, FLI=11.429, F=3.100; P<0.05), and the juveniles grew faster under LD 14:10 cycle and 2000 lx. Second, the feed intake (FIw) was also affected by light intensity, photoperiod and the relationship between them (FP=15.411, FLI=15.501, F=21.866; P<0.05), and the FIw increased with the lengthening of days and increased of light intensity then decreased, respectively. Third, the food conversion efficiency (FCEw) was affected significantly by photoperiod and the relationship between light intensity and photoperiod, but it wasn't affected by light intensity (FP =18.416, F=8.845; P<0.05; FLI =2.549, P>0.05). Fourth, the body crude lipid content and energy content decreased with the water content being increased with the increase in final body weight. The juveniles gained the higher FIw under 2000 lx and LD 14:10 cycle and the higher FCEw under LD 14:10 cycle, so LD 14:10 cycle-2000 lx maybe the better illumination condition of the intensive A. japonicus culture industry.7. The effects of light intensity on the oxygen consumption rate and ammonia-N excretion rate of 11.43±0.68 g sea cucumber Apostichopus japonicus were examined at 16℃, and six light intensities were 0 lx, 100 lx, 500 lx, 1000 lx, 2000 lx and 3000 lx, respectively. The results were as follows: Light intensity had significant effect on the oxygen consumption rate (OCR) and ammonia-N excretion rate (AER) of juvenile A. japonicus. First, the OCR of A. japonicus decreased with the increase of light intensity then increased. And the OCR under 2000 lx was significantly lower than the other light intensities (P<0.05), and 3000lx was significantly higher than the other light intensities (P<0.05) except 0lx (P>0.05). Second, the AER also decreased with the increase of light intensity then increased. And the AER under 2000 lx was significantly lower than the other light intensities (P<0.05), and 0 lx was significantly higher than the other light intensities (P<0.05) except 3000 lx (P>0.05) with 3000 lx being higher than 500 lx and 1000 lx (P<0.05). Third, light intensity also had significant effect on the O:N rate (P<0.05), and the O:N rate increased with the increase of light intensity then decreased. The O:N ratios indicating that A. japonicus mainly utilized lipid and carbohydrate as its energy sources, while the percentage of lipid and carbohydrate increased with the increase of light intensity then decreased.8. The effects of photoperiod on the diel rhythm of the oxygen consumption rate and ammonia-N excretion rate of 13.71±1.71 g sea cucumber Apostichopus japonicus were examined at 16℃and 2000 lx, and five photoperiods were LD 0:24 cycle (DD cycle), LD 10:14 cycle, LD 12:12 cycle, LD 14:10 cycle and LD 24:0 cycle, respectively. The results were as follows: There were diel rhythm of oxygen consumption rate and ammonia-N excretion rate under different photoperiods with the positive peak of A. japonicus mostly appeared at dark while the negative peak appeared at light, and it was more definite under DD cycle and LD 24:0 cycle. There were significant differences among the mean oxygen consumption rates of A. japonicus under different photoperiods (P<0.05), and they were significantly larger under DD cycle and LD 24:0 cycle than the other photoperiods (P<0.05). There were also significant differences among the mean ammonia-N excretion rates of A. japonicus under different photoperiods (P<0.05), and they were significantly larger under DD cycle and LD 24:0 cycle than the other photoperiods (P<0.05). The O:N ratios of A. japonicus were also affected significantly by different photoperiods and they were between 12.16~27.45, and the O:N ratios of A. japonicus under LD 24:0 cycle and DD cycle were significantly lower than the other treatments (P<0.05).