by Cláudia Figueiredo-Silva, Zinpro, USA
Zinc (Zn) was identified as an essential human micronutrient in 1961. Zn deficiency symptoms include growth retardation, immune insufficiency, chronic inflammation, skin abnormalities, impairment of wound healing, persistent diarrhea, loss of appetite and brain dysfunctions, among others, in both humans and animals. In addition, Zn is a structural constituent of ∼750 Zn-finger transcription factors enabling gene transcription and is a catalytic component of approximately 2,000 enzymes, encompassing all six classes (hydrolase, transferase, oxido-reductase, ligase, lyase, and isomerase). Hence, Zn is essential for cellular processes, including growth and development, as well as DNA synthesis and RNA transcription.
Although information on Zn functions in aquatic species is limited, the basic metabolic functions of trace minerals (TMs) and particularly Zn are recognised to be similar across species (NRC, 2011). Zn is known to exert beneficial effects beyond growth performance, such as bone and nervous system development, improvements in reproduction, reductions in oxidative stress and increased resistance to disease in fish and shrimp.
A common cause of Zn deficiency is malnutrition. Illness and/or infection and high phytate-containing diets reduce Zn bioavailability by inhibiting uptake. The replacement of fish meal (FM) in aquaculture diets may significantly reduce the Zn content while increasing levels of anti-nutritional factors, e.g. phytic acid. Phytic acid may bind TMs and make them less available for absorption, with direct effects on performance. As supplements, mineral amino acid (AA) complexes have an absorption advantage over inorganic minerals, because they are minimally antagonised by dietary components like phytic acid and use AA-transporters instead of common metal ion transporters (Gao et al. 2014; Sauer et al. 2017).
Paripatananont and Lovell (1995) were the first to demonstrate that the Zn-methionine complex was three to five times more bioavailable than inorganic Zn (ZnSO4) in meeting growth requirements of channel catfish fed purified and practical diets containing phytic acid, respectively. Davis et al. (1993) reported that L. vanammei required 33 ppm of Zn to maintain normal growth and maximise Zn concentrations in hepatopancreas. In the same study, supplementation with 200 ppm Zn (inorganic source) was required to overcome depressed Zn bioavailability caused by phytates and return Zn levels in hepatopancreas back to that observed in semi-purified diets without phytate.
Below, are two recent studies that demonstrate how adjusting Zn level and source in practical L. vannamei diets can influence growth, health and quality.
Study I, conducted by Yuan et al. (2020),
Comparing growth performance, immune status and meat quality response to partial or complete replacement of inorganic Zn with Zn-AA complex (ZnAA at 0.5x rate).
Study II, conducted by Jintasataporn et al. (2015)
Comparing growth performance, immune status and meat quality response to partial or complete replacement of inorganic mineral sources of Zn, Mn, Cu, Fe and Se with mineral-AA complexes, (ZPM, Zinpro Performance Minerals at 0.5x rate).
Benefits of adjusting Zn level and source on growth performance
Zn supplementation in practical shrimp diets has positively and significantly affected growth and feed conversion ratio (FCR), despite high FM inclusion level. Importantly, supplementation with a ZnAA complex at 0.5x rate (60 ppm Zn as ZnAA) compared to an inorganic source at full rate (120ppm as zinc sulfate) maintained shrimp growth and FCR, showing that ZnAA complex is a more effective Zn source. The most efficient (lowest) FCR was seen when combining 60 ppm Zn as ZnSO4 + 60 ppm Zn as ZnAA. This indicated higher Zn supplementation levels may be required to maximise shrimp performance and FCR.
Replacement of inorganic mineral premix (sulfates) with mineral-AA complexes at a half-rate of inorganic (ZPM at 0.5x) resulted in a numerically higher final body weight and 8.3 percent reduced FCR. Return on investment (ROI), measured by additional income over feed cost, was 16 percent more for shrimp fed ZPM at 0.5x rate vs inorganic minerals.
Benefits of adjusting Zn level and source on health status
Zn supplementation in practical shrimp diets significantly enhanced antioxidant capacity and immune-related enzymes as indicated by increased Cu-Zn SOD, AKP, ACP and LZM activities. Activity of hemolymph phenoloxidase, a crucial component of the shrimp immune system, significantly increased when ZnSO4 was partially or completely replaced with a ZnAA complex. In addition, the hepatopancreas antioxidant capacity and immune-related enzyme activity was higher in shrimp fed a combination of ZnSO4 and ZnAA complex or ZnAA complex at 0.5x rate (60 ppm Zn as ZnAA) of inorganic (120 ppm).
Partial or complete replacement of an inorganic mineral premix with mineral-AA complex premix (ZPM Zn, Mn, Cu, Fe and Se) improved shrimp immune status, as indicated by the increased hemocyte count and phenoloxidase activity. Importantly, the cumulative mortality of shrimp challenged with Vibrio harveyi was significantly reduced when the mineral inorganic premix was partially or completed replaced with mineral-AA complex.
Benefits of adjusting Zn level and source on product quality
The role Zn plays in shrimp goes beyond growth performance and immune status. Zn level and source had a significant effect on shrimp quality, namely drip and thaw loss.
Supplementation of the ZnAA complex in combination with ZnSO4 or at half-rate of inorganic, significantly reduced drip loss in muscle and thawing loss in whole shrimp. Supplementation with 120 ppm Zn from ZnSO4 did not affect whole shrimp or muscle drip loss. Moreover, partially (at 0.5x rate) or complete inorganic mineral premix replacement with a mineral-AA complex premix also reduced drip loss of peeled shrimp four days post-refrigeration. Thus, ZnAA complex supplementation proved superior to inorganic zinc supplementation for improved product quality.
Implications
Supplementation of 60 ppm Zn as Zn-AA complex in shrimp diets alone or in combination with other mineral-AA complexes proved an efficient approach in promoting shrimp growth, antioxidant capacity, immune response and product quality.
The high bioavailability of mineral-AA complexes may contribute to a more cost-efficient production of shrimp while decreasing nutrient excretion into the environment, making it a more sustainable choice. Potential additional benefits of Zn supplementation at levels higher than 60 ppm (Zn) in shrimp fed low or FM-free diets and grown in the field and thus under more challenging conditions are predictable and should be investigated.
References
Davis, D. A., A. L. Lawrence, and D. M. Gatlin III. 1993. Evaluation of the dietary zinc requirement of Penaeus vannamei and effects of phytic acid on zinc and phosphorus bioavailability. J. World Aquacult. Soc. 24: 40–47.
Gao, S., T. Yin, B. Xu, Y. Ma, and M. Hu. 2014. Amino acid facilitates absorption of copper in the Caco-2 cell culture model. Life Sci. 109:50–56.
Jintasataporn, O., T. Ward, S. Chumkam, and O. Jintasataporn. 2015. The Efficacy of Mineral-Amino Acid Complex (Zn, Mn, Cu, Fe and Se) in Diets to Growth Performance, Immune Status and Meat Quality of White Shrimp, Litopenaeus vannamei. Aquac. Indones. 16:33-37.
Paripatananont, T. and R. T. Lovell. 1995. Chelated zinc reduces the dietary zinc requirement of channel catfish, Ictalurus punctatus. Aquaculture, 133:73-82.
Sauer, A. K., S. Pfaender, S. Hagmeyer, L. Tarana, A. K. Mattes, F. Briel, S. Küry, T. M. Boeckers, and A. M. Grabrucker. 2017. Characterization of zinc amino acid complexes for zinc delivery in vitro using Caco-2 cells and enterocytes from hiPSC. Biometals, 30(5):643-661.
Yuan, Y., J. Luo, T. Zhu, M. Jin, L. Jiao, P. Sun, T. L. Ward, F. Ji, G. Xu, Q. Zhou. 2020. Alteration of growth performance, meat quality, antioxidant and immune capacity of juvenile (Litopenaeus vannamei) in response to different dietary dosage forms of zinc: Comparative advantages of zinc amino acid complex. Aquaculture 522:735120
