Читать книгу Clinical Guide to Fish Medicine - Группа авторов - Страница 109

Systems are often categorized as open, semi‐open, or closed. Open systems have continuous water input and discharge, usually from a natural body of water. Examples include pens in natural waterways, raceways, and aquariums where water flows through each system. Semi‐open systems also have a mechanism to recirculate some or all of the water. Closed systems do not have continuous water input or discharge. Examples of closed systems include home aquariums, intensive aquaculture systems, ponds, and most transport containers. While closed systems can be managed using a “dump and fill” approach, where some or most of the water is occasionally removed and replaced, it is more common for closed systems to be managed with recirculation through life support equipment. For this reason, the terms closed and recirculating are often used interchangeably.

Closed systems are the most complex as they are completely dependent on equipment and management practices to condition the water and sustain life. In closed systems, predictable changes occur to the water due to natural biological processes. These changes, if not countered by the LSS, will endanger fish. They include:

 Dissolved oxygen is used and carbon dioxide is produced through respiration.

 Nitrogenous wastes such as toxic ammonia, nitrites, and nitrates are produced from animal waste, uneaten food, and detritus.

 pH fluctuates as buffers are used or added and carbon dioxide is produced.

 Particulate and dissolved organic carbon (DOC) build up.

 Anions and cations like carbonates and calcium are used.

 Pathogen load may increase.

The LSS is used to manage and maintain appropriate levels of dissolved gases, nitrogenous wastes, and pathogens. This may involve gas exchange, mechanical, physicochemical, and biological filtration, and ultraviolet (UV) or ozone disinfection.

In all three system types, life support equipment may also be needed to process and manage incoming and discharged water to ensure suitable water condition.

The scale of LSSs varies enormously. For smaller aquariums, there are standard, off‐the‐shelf components readily available. As system size increases, LSSs often require more design and construction effort to help support fish health and system management. For the largest aquarium systems, engineers are often involved in the design and maintenance of the LSS.

Most of the filtration methods currently used for LSSs have their basis in municipal wastewater, drinking water, and swimming pool industries. These have very different goals from living systems, such as high levels of disinfection. Newer approaches are incorporating the natural stabilizing processes of wild aquatic systems. This understanding may provide more efficient and cost‐effective life support for aquatic animals in the future.