Читать книгу Fundamentals of Aquatic Veterinary Medicine - Группа авторов - Страница 16

Aquaculture is the farming of aquatic organisms including fish, mollusks, crustaceans and aquatic plants, with some sort of intervention in the rearing process to enhance production, such as regular stocking, feeding, and protection from predators. Farming also implies individual or corporate ownership of the stock being cultivated. Aquatic ecosystems provide the basis for aquatic production. The worldwide practice of aquaculture runs the gamut from low‐technology extensive methods to highly intensive systems. Although used for housing and maintaining ornamental fish, similar aquasystems are found in large public aquaria and private homes and are discussed in this chapter. The term ‘life‐support system’ is understood as a complete system that satisfies the physiological needs of an aquatic organism in question. Diagrams and photographs of examples of life‐support systems can be found in Chapter 3.

Managed ecosystems form the basis for aquaculture production, which has been widely offered as a means of complementing and ultimately supplementing traditional fisheries. Here, unlike fisheries, inputs, production processes and quality of output can be at least partially controlled, and ownership, care and environmental responsibility might be more easily established. By removing natural constraints to survival and productivity, and by husbandry and management, production need be limited only by availability of simple inputs such as land, water, seed (hatchling, spawn, fry or fingerling), fertilizers and feeds. The design of a life‐support system is dependent on the type of aquatic system in question, being either a flow‐through system or a closed system. In a flow‐through system, the main elements include a spigot or waterfall that is adjustable for the amount of water flow necessary, a drain that is usually positioned at the opposite end of the system, potential for increased aeration, and, possibly, temperature controls.

A closed system may be a pond, tank or aquarium. In a pond, the most important elements are circulation and aeration, and it may also include a filtration system. Tanks and aquaria usually require a filtration system, aeration, and often temperature control. The source of the water is important when deciding on the type of aquatic system and the type of life‐support system. A large well, river or lake is necessary for a flow‐through system because of the high volume of water that is needed to maintain proper water quality. If city water is being used in a system, it is important to have a reservoir to dechlorinate any new water entering the system. In recirculating systems, water circulation and purification is accomplished with the use of powered pumps and filtration systems. The type of equipment used will depend on the type of fish, number of fish and the expected growth rate of those fish.

In aquaculture, high‐intensity growth of fish leads to higher ammonia levels and waste production. The output of the pump should allow for a flow of the full volume of water in the system to pass through the filter every two to three hours. This is referred to as the “turnover time”. It is calculated by dividing the water volume in the system by the volume per time rating of the circulation, measured at the return (the volume/time is variously described in gallons/minute or hour as GPM, GPH or metric m³/hour). In tanks and ponds, flow rates are very variable, from less than five minutes in the smallest aquaria to more than 10 hours in larger ponds. Submersible pumps with low maintenance sealed impellors may be used in small ponds and aquaria, but larger aquasystems typically use external pumps. The filtration system should contain biological media with an appropriate surface area to allow for detoxification of ammonia based on the number of fish. On average, 1 m² of active surface area can process 1 gram of ammonia every 24 hours (Wildgoose, 2001).

Monitoring of the system may be fully automated or may be performed by individuals. The benefits of automated monitoring equipment include the ability to set alarms for power outages, changes in dissolved oxygen and large changes in ammonia. Some systems are able to calculate flow rates and water usage, which is beneficial for production calculations. Monitoring should include ammonia, nitrite, nitrate, dissolved oxygen, temperature, total alkalinity and pH to assure proper water quality parameters.