Effect of Vitamin D3 Supplementary Shrimp Diet on Cuticle Formation of the Pacific White Shrimp (Litopenaeus vannamei)

Abstract

Background and Objectives : The requirement of vit D₃ in form of 1,25-Dihydroxy-Vitamin D₃ (Calcitriol) for white shrimp (Litopenaeus vannamei) is still rather lacking  in term of cuticular formation and mineralization due to the direct and indirect affect the success of molting, and subsequently affects the growth opportunity and survival rate. The study on effectiveness of vitamin D₃ in form of calcitriol to promote the shrimp exoskeleton in terms of ions content in cuticle and cuticular structure of L. vannamei were investigated to further decide the optimal level of vit D₃ in a practical diet be part of effectiveness to increase the shrimp production of Thailand.  

Methodology : The three treatments followed by the concentrations of vitamin D₃ (AcD) at 100 mg (AcD100), 150 mg (AcD150) and 200 mg (AcD200) vit D₃ kg^-1 diet and without AcD (Control) were designed with three replications using completely randomized design (CRD). Three replications were used in the study. The healthy L. vannamei juvenile aged 45 days with 12.50 ± 0.65 g in body weight and 9.90 ± 0.50 cm in total length from intensive pond of private sector were previously acclimated during 10 days in laboratory before sampling to the 500L experimental circular fiberglass tank with 1.05 m in diameter. The experimental shrimps were held in 25 ppt medium at 70 ind./m². Water was exchanged with debris every week and exchanged by 50% of cleaned water. Experimental shrimps were fed the experimental diets which was formulated to satisfy the nutritional requirement of L. vannamei with the isonitrogenous (38.15% crude protein) and isolipidic (7.6% crude lipid which stored in individual bag at 4°C in refrigerator for the whole trial duration. The ration of 5% in total wet weight and four times daily (08.00 am, 01.00 pm, 05.00 pm and 09.00 pm) were operated for 30 cultured days. Water quality parameters as salinity, temperature, dissolved oxygen (DO), alkalinity, nitrite and ammonia were monitored every week at 09.00 am and 03.00 pm. To controlled sunlight and temperature, blue coloured plastic covered the tank. At termination, the experimental shrimps at B (Postmolt) and Do (Early Premolt) stages (10 samples/replication) were individually sampled for examining ions and cuticular structure as cuticle thickness and number of layers within cuticle using carapace near the posterior rostral ridge using scanning electron microscopy (SEM) coupled with energy dispersive x-ray spectroscopy. The combination of SEM and EDS allows for the analysis of both the quantity of X-rays emitted and their energy, enabling the identification and quantification of chemical elements present at detectable concentrations in percentage by weight. Analysis of variance with one-way ANOVA and Duncan’s New multiple range test using SPSS software were used for statistically different the results among treatments. The level of significant difference was set at p< 0.05.

Main Results : The results found that cuticle thickness and number of layers of shrimp cuticle at B (45.2 ± 2.9 m and 25.5 ± 1.9 layers) and Do stage (97.5 ± 8.4 m and 69.4 ± 4.9 layers) of AcD200 group were the most significant highest (p<0.05), followed by AcD150 group with non-significant difference (p>0.05) for Do stage, which corresponded with higher percentage of Ca (11.23 ± 0.42%), Mg (0.65 ± 0.09%), Mn (0.71 ± 0.13%)  and P (5.32 ± 0.87%) in cuticle at B molt stage  (p<0.05) and Ca (13.23 ± 0.31%), C (56.13 ± 4.35%) and O (34.34 ± 2.15%) in cuticle at Do molt stage (p<0.05). The thickness and number of layers of cuticle at B and Do stages of AcD 150 and AcD100 groups were not significant different (p>0.05) but their values of both groups were significantly higher than that of control (p<0.05). The percentages of Cu, K, Na, O, C and Cl of shrimp cuticle at B molt stage and the percentages of Cu, K, Na, Mg, Mn and Cl of shrimp cuticle at Do molt stage were not significantly different (p>0.05) among groups respectively. All parameters of water quality as salinity, temperature, DO, alkalinity, nitrite and ammonia among the treatments were not significantly different (p> 0.05) and their values were acceptable for shrimp throughout the experimental period.

Conclusions : Finally, the research results demonstrate the supplementation of at levels of 150-200 mg kg^-1 in diet for raising L. vannamei shrimp is the most suitable to contributes the higher mineralization rate of Ca, Mg and Mn in form of phosphate for post molt stage and carbonate form for intermolt stage to faster process of cuticle formation. It is high possibility that vit D₃ can improve the regulation of Ca and P metabolism and absorption to promote the early mineralization of postmolt cuticle led to the suprior nucleation of  Ca and CO₃^-to better formation of the intermolt cuticle. These results highlight the benefits of supplementing the suitable concentration of vit D₃ in term of precision nutrition to support the cuticle formation in L. vannamei shrimp results in the higher growth performance and survival rate.