Mineral Bioavailability and Its Role in Aquatic Animal Nutrition
By Dr.Wiphada Mitbumrung, Ph.D. Applied Marine Biosciences — Wed Feb 18 2026
Mineral bioavailability in shrimp culture is fundamentally a water-chemistry issue. A mineral you add is only useful if it remains bioavailable, meaning it stays dissolved in the water as free or readily available forms, not locked up in particles or precipitates, so shrimp can absorb it efficiently through the gills or other membranes. In ponds, the same element can exist simultaneously as free ions, inorganic complexes, organic complexes, colloids, adsorbed forms on clays and biofloc, or as precipitated solids. For this reason, the total mineral concentration measured in pond water does not necessarily represent the fraction that is truly free and ready for uptake by the shrimp. In commercial mixed-mineral products for shrimp ponds, the choice of mineral salt form matters as much as the element itself, because bioavailability in water treatment is largely driven by how fast a compound dissolves and how easily it precipitates under pond pH and alkalinity conditions. For calcium as the primary macro-mineral for molting and shell formation, the ideal source is one that becomes immediately available upon contact with water and remains stable long enough to be absorbed. The table below shows common calcium and magnesium compounds used in aquaculture and their relative solubility in water.
Example of calcium chloride, commonly present in the form of CaCl2・2H2O which dissociates rapidly. CaCl2・2H2O → Ca2+ + 2 Cl- + 2H2O This increase bioavailable Ca2+ without raising pH
Water-chemistry parameters that control mineral bioavailability
Once a mineral compound dissolves, whether it stays dissolved and therefore available for uptake is controlled by pond water chemistry. The most important parameters are:
pH: pH controls the balance between dissolved ions and insoluble solids. As pH rises, many metals and alkaline-earth minerals are more likely to form hydroxides or carbonates and precipitate. High afternoon pH can quickly reduce the free/bioavailable fraction even if total calcium/magnesium looks adequate.
Alkalinity: Alkalinity provides carbonate species (HCO₃⁻/CO₃²⁻) that can react with Ca²⁺ to form CaCO₃. In high-alkalinity ponds, especially when pH spikes, calcium added in a highly soluble form can still be pulled out of the water column by carbonate precipitation.
Hardness and ionic balance: Hardness reflects the pool of Ca²⁺ and Mg²⁺ already present. Very imbalanced Ca:Mg or sudden large additions can push the water toward supersaturation, increasing the risk of precipitation or adsorption onto particles rather than remaining available.
Salinity: In brackish or seawater, ions form inorganic complexes (e.g., CaSO₄, MgSO₄). These complexes reduce the free ion activity even when the mineral is dissolved, changing what shrimp can physiologically take up.
Phosphate: Phosphate can bind calcium strongly and form calcium phosphate precipitates, one common reason calcium additions disappear from the water. In reduced (low-oxygen) sludge zones, sulfide can also bind certain trace metals and reduce their availability.
Dissolved organic matter: Organics can complex minerals, sometimes stabilizing them in solution, sometimes reducing the free-ion fraction. Biofloc, clay, and fine particles provide surfaces for adsorption/ion exchange, which can shift minerals from dissolved forms into particle-bound forms.
TSS/turbidity and clay content: The higher the suspended solids and reactive clays, the more likely minerals, especially trace elements, are to become adsorbed or incorporated into floc, lowering immediate bioavailability.
Temperature: Solubility and reaction rates change with temperature. Warmer water often accelerates precipitation/adsorption kinetics and can intensify daily pH swings via phytoplankton activity.
Application method: Local hot spots from dumping concentrated minerals can cause instant precipitation. Pre-dissolving, applying in smaller split doses, and ensuring good distribution help keep ions in solution longer.