Environmental impacts of brass mesh nets on open ocean aquaculture pens in tropical marine environments

Abstract

Aquaculture pens with brass mesh were installed at commercial fish farms in two locations, Panama and Mexico. Measurements of copper and zinc levels in the water and sediments were monitored over 468 and 435 days for the Panama and Mexico sites respectively. Additional chemical parameters were also measured including dissolved organic carbon in the water column and total solids, total organic carbon, total sulfides, redox potential and acid volatile sulfides and simultaneously extracted metals in the sediments. Measurements were taken at a reference site 1000 m away from the pens perpendicular to the dominant current direction, as well as 50 m upstream, 50 m downstream and adjacent to the pens. Muscle, skin and liver samples were taken from cobia (Rachycentron canadum) produced at the Panama site and analyzed for copper content.The dissolved copper levels at both farms stayed below 1 μg/L at all times. There was no significant difference in the dissolved copper levels between the reference site and other measurement sites at either location. There was also no observable increase in dissolved copper levels over time at the Mexico location although there was a significant difference in dissolved copper levels between the sampling days at the Panama location. Zinc concentrations also remained within safe levels, never exceeding 0.82 μg/L at any point. Copper and zinc levels in the sediments did not show a significant increase over time. The copper levels in tissue samples from the muscle tissue of the cobia raised in a brass mesh pen at the Panama site were 19% higher than those raised in the plastic mesh pen. The elevated copper levels are well below recommended daily intake levels and do not pose a risk to human health. There was no significant difference in copper levels of the skin or liver tissue samples. The absence of any increase in liver copper levels suggests that the fish's physiology and welfare are not impacted by brass mesh.The findings suggest that brass mesh is environmentally compatible with high energy marine environments and a commercially viable product for open ocean aquaculture farms.