The basic components of a life support system are a vessel that houses the animals, and if water is to be recirculated, the filtration components, and a sump or reservoir (area to collect water before and/or after treatment). Understanding these component parts can help the veterinarian determine how it may impact animal health and disease management. Additional study will be required for veterinarians who need to develop greater knowledge and skills for aquatic practice.
There are three basic types of filtration: biologic, mechanical, and chemical. All recirculating systems have biologic and mechanical components, and most also include a chemical component. Some types of filters provide more than one of these functions. Veterinarians should familiarize themselves first with basic filtration and later, with more complex system designs.
Biologic Filtration for Aquatic Life Support Systems
Biologic filters remove nitrogenous waste from the system. Fish excrete ammonia directly from the bloodstream via passive diffusion across the gill epithelium. Biologic filters provide substrate and massive surface area for nitrifying bacteria to live. These bacteria are ubiquitous in the environment and grow well when nitrogenous compounds (ammonia and nitrite) are present in the water column; they also require both oxygen and a carbonate source, which must be provided by the water and filter design. Examples of biologic filters are plastic plenums placed in the bottom of home aquaria, fluidized bed filters common in commercially designed systems, and an array of bead and sand filters sold for use in ornamental pond and aquaculture units.
Mechanical Filtration for Aquatic Life Support Systems
Mechanical filters are always placed before biologic filters in the system design. Mechanical filters typically receive water leaving the vessel housing animals and remove large particulate matter (ie, uneaten food, fecal material, debris) before water comes into contact with the biofilter. Large particles can clog a biofilter, resulting in channeling and development of anoxic areas that greatly compromise function of the unit. Mechanical filters can be as simple as floss or foam pads receiving a stream of water, or much more complex. Sand and bead filters are commonly used and have dual functions of mechanical and biologic filtration.
Chemical Filtration for Aquatic Life Support Systems
Chemical filters provide a way to treat the water. Activated carbon is very commonly used to remove toxins and colored compounds from aquarium water, which helps maintain clarity. Activated carbon filters may also be placed on inflowing water to remove chlorine and/or chloramine from municipal water. Activated carbon filters can also be used to remove treatment chemicals from water before discharge to municipal sewers. Other examples of chemical filters include protein skimmers and foam fractionators, which are commonly used in marine systems to remove proteinaceous waste (decreasing the load on the biofilter); ultraviolet light sterilizers, which, if sized appropriately, remove potentially pathogenic organisms from the water column; and ozone, which clarifies water and kills microbes. Ozone is common in large commercial aquaria and requires a de-gassing area before the treated water comes back into contact with fish. Malfunction of ozone units can be hazardous to humans as well as animals housed in aquarium systems.