Effects And Mechanism Of Ca²⁺ Concentration On The Molting And Growth Of Juvenile Litopenaeus Vannamei

A series of indoor experiments were conducted to investigate the effects of ambient Ca²⁺ concentrations on the molting, growth, energy budget, ion contents and enzyme activity of Litopenaeus vannamei. The primary results were listed below.1 The effects of low Ca²⁺ concentration fluctuation on the molting, growth and energy budget of juvenile Litopenaeus vannameiThe effects of Ca²⁺ concentration fluctuation on the molting, growth and energy budget of juvenile Litopenaeus vannamei with an initial wet body weight of (1.459±0.006)g was investigated. Artificial seawater with salinity of 30 was used in the experiment, and the Ca²⁺ concentration of the control treatment C360 was 360 mg·L^-1 throughout the experiment, while the treatments C300, C240, C180 and C120 were subjected to different Ca²⁺ concentration fluctuations, and the amplitudes are 60 mg·L^-1, 120 mg·L^-1, 180 mg·L^-1 and 240 mg·L^-1, respectively. After a 40-day feeding trial, the results were as follows: 1. The molt frequency (MF) of the shrimp in the treatment C120 was (11.0±0.5) %.d^-1 and significantly higher than the mg·L^-1 other four treatments (P<0.05), and there are no significant differences among the four treatments (P>0.05); 2. The specific growth rates (SGR) of the shrimp in the five treatments were as follows: C360> C300> C240> C180> C120, and the minimal one occurred in the treatment C120 (P<0.05); 3. There are no significant differences in feed intakes (FI) of the shrimp in the five treatments (P>0.05), but the food conversion efficiency (FCE) of the shrimp in the treatment C120 was significantly lower than the other four treatments (P<0.05); 4. In the experiment, the percentages of energy deposited for growth (G), lost for respiration (R), lost in exuvia (E) to the energy consumed in food (C) were affected by the different Ca²⁺ concentration fluctuations significantly (P<0.05). These results showed that the biggest amplitude of Ca²⁺ concentration fluctuation could increase the molt frequency of the juvenile Litopenaeus vannamei, but it had adverse effects on the growth of shrimp.2 The effect of different Ca²⁺ concentration fluctuations on the molting, growth and energy budget of juvenile Litopenaeus vannameiA 40-day experiment was conducted to investigate the effects of different Ca²⁺ concentration fluctuation on the molting, growth and energy budget of juvenile Litopenaeus vannamei with an initial body weight of (1.202±0.006)g. The Ca²⁺ concentration of the control group C385 was 385 mg·L^-1 throughout the experiment, while the Ca²⁺ concentration of the C591, C803, C1155 and C2380 groups periodically fluctuated from 385 mg·L^-1 to 591, 803, 1155 and 2380 mg·L^-1, respectively. The results were as follows: 1. The molting frequency (MF) of the shrimp in the Ca²⁺ concentration fluctuating groups was significantly higher than those in the control group (P<0.05); 2. The specific growth rates (SGR) and feed intake (FI) of the shrimp in the C591 and C803 groups were significantly higher than those in other groups (P<0.05); 3. No significant differences in food conversion efficiency (FCE) were found among all groups (P>0.05); 4. The shrimp in C591 and C803 groups spent significantly less energy in respiration, while depositing significantly more energy for growth than those in other there groups (P<0.05). These results showed that proper Ca²⁺ concentration fluctuations could increase the molting frequency and growth rate of the juvenile L. vannamei, and according to the regression formula made by SGR and range of Ca²⁺ concentration fluctuation, periodically enhanced Ca²⁺ concentration of 295 mg·L^-1 in the seawater was suggested to be used in shrimp culture.3 Effects of constant Ca²⁺ concentration in salinity fluctuations on growth and energy budget of juvenile Litopenaeus vannameiA 50-day experiment was conducted to investigate the effects of constant Ca²⁺ concentration in salinity fluctuations on growth and energy budget of juvenile Litopenaeus vannamei with an initial wet body weight of (0.525±0.002)g was investigated. The salinity and Ca²⁺ concentration of control group S0 were kept 30‰and 385 mg·L^-1 throughout the experiment, respectively, while the ranges of salinity fluctuations of the treatment groups S5 and S5C, S10 and S10C, S15 and S15C, S20 and S20C were 5, 10, 15 and 20‰, respectively. The Ca²⁺ concentration of the treatment groups S5, S10, S15 and S20 (salinity fluctuation groups) changed with salinities, while the Ca²⁺ concentration of the treatment groups S5C, S10C, S15C and S20C (constant Ca²⁺ concentration groups) was kept 385 mg·L^-1 during the experiment. The results were as follows: 1. There were no significant differences in SGR of shrimp in salinity fluctuation groups (P>0.05); But shrimp in the groups S15C and S20C had significantly higher SGR than those in the groups S5C and S0 in constant Ca²⁺ concentration groups (P<0.05); 2. Results of the t-test showed that significant differences in SGR were also found between S15 and S15C (P=0.012), and between S20 and S20C (P=0.013); 3. The shrimp in groups S15C and S20C deposited significantly more energy for growth and spent significantly less energy in respiration than those in groups S15 and S20 (P<0.05), respectively. These results showed that compared with constant salinity and fluctuating salinities, the growth of shrimp under constant Ca²⁺ concentration in proper salinity fluctuations could be better.4 Effects of Ca²⁺ concentration on survival and growth of juvenile Litopenaeus vannamei, reared in low salinity watersEffects of Ca²⁺ concentration on survival and growth rate of juvenile Litopenaeus vannamei, reared in low salinity waters were investigated,and two trials were conducted in the present study. Low salinity waters were made by adding different chemicals into distilled water, and Ca²⁺ concentrations were adjusted by adding CaCl₂ into the water. Survival trial was conducted in 0.5, 5 and 10 salinity waters. Ca²⁺ concentrations (1, 5, 10 and 15 mg·L^-1), (5, 15, 25 and 35 mg·L^-1) and (5, 20, 35 and 50 mg·L^-1) were made in 0.5, 5 and 10 salinity waters, respectively. Shrimp (initial wet body weight 1.395±0.158 g) molted at least once during the trial. Ca²⁺ concentration was found to significantly increase shrimp survival in low salinity waters; Growth trial was conducted in"freshwater"(S<1), and the Ca²⁺ concentration of treatment C5, C15, C25, C50 and C100 was 5, 15, 25, 50 and 100 mg·L^-1, respectively. The results were as follows: 1. The molting frequency (MF) of the shrimp in the treatments C50 and C100 was significantly higher than those in the control group (P<0.05); 2. The specific growth rate (SGR) and food conversion efficiency (FCE) of the shrimp in the treatment C15 were significantly higher than those in the treatment C5 (P<0.05); 3. No significant differences in feed intake (FI) were found among all groups (P>0.05); 4. The shrimp in treatment C15 spent significantly less energy in respiration, while depositing significantly more energy for growth than those in the treatment C5 (P<0.05). These results suggest that relatively high Ca²⁺ concentration would improve the survival and growth of shrimp in inland shrimp culture.5 Effects of ambient Ca²⁺ concentration on the Ca, Mg, K and P contents in the exoskeleton, hemolymph, hepatopancreas and muscle of the juvenile Litopenaeus vannamei during the molt cycleThe effects of ambient Ca²⁺ concentration on the content of Ca, Mg, K and P in the exoskeleton, hemolymph, hepatopancreas and muscle of the juvenile Litopenaeus vannamei during the molt cycle were investigated. Five molt states (early postmolt, late postmolt, intermolt, early premolt and late premolt) were dissected for analysis of content of Ca, Mg, K and P in the present experiment. Artificial seawater with salinity of 30 was used in the experiment, and the Ca²⁺ concentration of the treatments C360, C300, C240, C180 and C120 were 360, 300, 240, 180 and 120 mg·L^-1, respectively. The fluctuations of Ca, Mg, K and P contents in different stages of the molting cycle: 1. Hemolymph had significantly higher content of Ca during late premolt stages than late postmolt (P<0.05), and content of Mg in hemolymph and hepatopancreas decreased from early molt stage to intermolt stage; 2. The content of Ca in hepatopancreas was highest in the intermolt stage, but P content in hemolymph, P and K content in hepatopancreas did not show significant changes during molt cycle (P>0.05); 3. Muscle had significantly higher content of Ca during early postmolt, late postmolt and late premolt stages than intermolt and late postmolt stages (P<0.05); 4. In exoskeleton the Ca and Mg levels were high in intermolt and early premolt stages and the lowest level was recorded in the early postmolt stage. The content of Ca in hemolymph, hepatopancreas and exoskeleton decreased with the decreasing in the ambient Ca²⁺ concentration, meanwhile, the content of Mg, K and P increased in the exoskeleton. The regression formula made by the content of Ca in exoskeleton (y) and the ambient Ca²⁺ concentration (x) was: y=-0.0014x²+0.836x-49.615(R²=0.8651, P=0.0000).The results showed that Ca, Mg, K and P contents in different tissues of the juvenile Litopenaeus vannamei were significantly affected by molt stage and ambient Ca²⁺ concentration.6 Effects of Ca²⁺ concentrations on the Na⁺-K⁺-ATPase activity, Carbonic anhydrase activity and expression of calreticulin of Litopenaeus vannameiThe effects of different ambient Ca²⁺ concentrations on the Na⁺-K⁺-ATPase activity, Carbonic anhydrase activity and expression of calreticulin of the marine shrimp Litopenaeus vannamei were investigated in the present study. The ambient Ca²⁺ concentrations of groups C120, C240, C300, C600 and C1200 were 120 mg·L^-1, 240 mg·L^-1, 360 mg·L^-1, 600 mg·L^-1and 1200 mg·L^-1, respectively, and C360 was the control group. The results showed that there were no significant differences in the activity of Na⁺-K⁺-ATPase activity among all experimental groups (P>0.05); The activities of Carbonic anhydrase in the gills of the shrimp in groups C120 and C1200 were lower than those in the control group C360 (P>0.05), and significantly lower than those in group C600 (P<0.05); Expressions of calreticulin at RNA level were lowest in hepatopancreas, and were highest in muscle of shrimp. Expressions of calreticulin at RNA level in gill and muscle of the shrimp in group C120 were significantly lower than those in the control group C360 (P<0.05). Expressions of calreticulin at RNA level in gill of shrimp in groups C600 and C1200 were significantly lower than those in the control group C360 (P<0.05), but there were no significant differences in the muscle among the three groups (P>0.05).