Potential applications of exposure to magnetic field in changing water properties and improving growth performance of selected aquaculture organisms
Abstract
This study intends to understand the effect of magnetic field on water properties and on aquaculture organisms. Magnetic water is produced when water is passed through a magnetic field which alters the state of the macromolecules of the water. Changes to the physico-chemical properties of magnetised water affect the biological properties of the organisms that consume or are exposed to it. This study is based on previous works reporting the positive effects of exposure to magnetic field on water properties, plant growth, plant germination, livestock-drinking water, fish fertilisation and against the backdrop of issues pertaining to water quality in recirculating aquaculture systems (RAS), which negatively impacted fish growth and hatchability rate of aquaculture species. First, this work evaluated the effect of exposure to magnetic field intensities of 0.10, 0.15, 0.20, 0.10+0.15, 0.10+0.20, 0.15+0.20, and 0.10+0.15+0.20 T on water qualities. The results showed significant (p < 0.05) increase in dissolved oxygen, pH, and conductivity by 17.3, 1.6, 3.0%, respectively, and a significant decrease of the ammonium level, specific conductivity, total dissolved solids, oxygen reduction potential, and chlorides by 25.3, 1.1, 1.4, 1.0, 16.9, 3.4%, respectively. A study on the effect of magnetically charged water on Artemia (Artemia salina) showed an increase of hatchability rate, from 49.3% for the normal water to 89.1, 88.4, and 69.5% for magnetised water of 0.10, 0.15, and 0.20 T, respectively. However, a decline in Artemia hatchability rate to 48.6, 42.3, 43.7, and 42.0% occurred when water was magnetised to 0.10+0.15, 0.10+0.20, 0.15+0.20, and 0.10+0.15+0.20T respectively. An increase of 64.7% in Artemia hatchability (H%) was attained in the water exposed to a magnetic field of 0.15 T for 20 hours compared with the control treatment at 41.7%. The increase of 86.3, 86.7 and 86.3% in red hybrid tilapia’s (Oreochromis sp.) hatchability rate (H%) were attained in water exposed to magnetic field intensities of 0.10, 0.15, and 0.20 T for 5 hours, compared to the control treatment at 78.8%. Increases of 55.0, 59.2, and 66.8% in catfish’s (Clarius gariepinus) hatchability rate (H%) were attained in water exposed to magnetic fields of 0.10, 0.15 and 0.20 T, compared to the control treatment at 51.7%. Significant decrease (p < 0.05) in feed conversion ratio by 14.9% and increase in body weight by 5.2% for jade perch (Scortum barcoo) and significant decrease in FCR by 30.7% and increased weight gain by 17.0% for red hybrid tilapia juveniles in RAS. The best results were obtained when using water exposed to magnetic field intensities of 0.10 and 0.15 T, respectively. The liver cells of the fishes grown in the control treatment and those in 0.10 T magnetic water exhibited a normal sinusoid organisation with no indications of lesions or abnormalities of the hepatocytes. In summary, the study demonstrated the benefits of using magnetically charged water for aquaculture due to increased hatchability of artemia, red tilapia, and catfish, and a better growth performance for jade perch and red hybrid tilapia culture in waters exposed to magnetic fields demonstrated significantly lower FCR, hence improve in fish productivity in RAS. Since the installation of the device is simple, low cost, and can be retro-fitted into existing systems, fish farmers can increase their aquaculture productivity.