Mineral Deficiencies and Aquaculture12 September 2016
Dr Bill McGraw, an Aquaculture and Environmental Scientist in Panama, provides an overview of minerals in aquaculture and human diets.
History of mineral depletion in the human diet
Mineral deficiencies in the human diet started with the invention of commercially available electricity in the 1870s. This advance in technology would result in the reduction of the use of wood fires for cooking, decreasing the need for disposal of wood ashes in gardens soils. Wood ash is an excellent fertilizer as it contains minerals such as calcium helping to balance ph, and trace elements aiding in plant growth, contributing to better human nutrition. Further to this, damming of rivers and streams to provide for the ever increasing demand for electricity led to decreased mineral inputs in much used fertile alluvial soils.
The late 1960s saw the beginning of modern commercial agriculture that brushed aside organic mineral-rich inputs such as manures used as a source of nitrogen, phosphorous, potassium and sulfur in favor of synthetic fertilizers containing no minerals outside of these four necessary major elements. These synthetic nitrate and phosphate fertilizers are water soluble and wash in local streams creating problems with eutrophication. Modern agriculture is the most widespread contributor to mineral deficiencies in humans in industrialized countries with reduced mineral concentrations in foods produced on mineral deficient soils.
Modern diets consisting of store bought, packaged, processed foods and the ubiquitous fast food restaurants remove the little available mineral nutrition from already mineral deficient foods. Diets of healthy traditional peoples such as aborigines of Australia and native Indian tribes of South America have been determined to contain four times the mineral concentrations of the modern processed diet consumed in industrialized countries even as far back as the 1930s.
By 1989, the recommended daily requirements of calcium, magnesium and zinc were not being met by more than 65% of the population of the United States. The Scientific American reported that from 1975 to 1997, calcium in 12 fresh vegetables decreased by 27% with similar findings in the British Food Journal declaring calcium reduction of 19% in 20 vegetables from the years of 1930 to 1980. Deficiencies were further induced with a lesser amount of whole foods being consumed in favor of foods of greater appeal, availability and convenience. The taste of fruits and vegetables has often been correlated with the amount of minerals they contain, in other words, "organic food from mineral rich soils tastes better", which likely contributes to current reduced fruit and vegetable consumption.
Obvious mineral deficiencies in humans can be apparent when considering well known conditions of anemia, osteoporosis, goiter, and stunted growth. However, lesser known correlations have been found between mineral concentrations of diet and water sources, and, increase or decrease in the health of associated populations. More traditional diets of people not exposed to modern agriculture and food processing, are known to result in much better dentition than their industrialized counterparts.
The world health organization stated that there are 2 billion people in the world suffering from mineral and vitamin deficiencies, with the majority found in the third world countries.
Necessary minerals and metabolism in aquaculture
Adding "salt" to prepared diets of fish has been documented to improve the growth of freshwater fish. This success is based on providing the necessary elements for digestion, growth, and excretion of culture animals. Secondarily, minerals or salt can be added to water to reduce osmoregulatory stress as an aid in transport, to reduce opportunistic pathogens in culture water, and to increase growth by reducing the energy required for osmotic balance.
Minerals such as sodium and calcium can be added to the diet or water which result in satisfying the mineral dietary requirements for fish culture. Pertinent to absorption, bioavailability and retention of a single mineral provided in the diet of fish may also be determined by the concentration of a metabolically contingent mineral. For example, such as the relationship is found between calcium and the bioavailability of zinc. Also, it is unknown how much of the mineral addition to the diet would be maintained in the fish and how much would be lost to the environment during normal osmoregulation and excretion as measured in TDS or total dissolved solids.
Excretion of nitrogen waste via the gills is the primary toxic nitrogen removal process in fish which is tightly coupled to sodium loss in order to maintain acid-base regulation in metabolism. This is apparent when examining how the acidity of culture water results in osmoregulatory stress due to decrease in plasma ions of fish in freshwater. Ion transport to maintain salts in the blood of freshwater fish occurs nearly exclusively at the gill surface while fish produce ample volumes of dilute urine.
Minerals, aquaculture and human nutrition
Fish is one of the cheapest sources of protein and minerals available. Mineral concentrations of aquatic animals, whether in excess or deficiency are based on minerals in the environment, as are other important nutritional compounds such as omega-3 fatty acids and beneficial pigments. Most of the common minerals needed for maintenance of every biochemical function in humans can be found in fish while every mineral known can be found in the ocean. Concentrations of minerals in the ocean are near exact proportions found in the blood of all humans, and in general, minerals in aquatic organisms increase with the salinity (TDS) in the water.
Mineral concentrations in fish vary between species and even between sizes within the same species.
Additional variation in mineral content can be found between sections of a fillet. Research conducted in 2002 demonstrated that iron and zinc were two major elements in cultured and wild sea bass with no differences found between the two types in terms of total mineral composition. Zinc has been identified as being deficient in the modern diet in industrialized countries as previously stated.
The understanding of the mineral content of fish would benefit greatly by examining the mineral content of waters in which they are grown, minerals in the diet and the possibility to increase the mineral content of fish by manipulating these two variables or by simply selecting higher mineral content waters for aquaculture.