Livestock

These are the very rare species of fishes and only eat meat. Bettas and jack Dempsey cichlids feed on worms which are live or freeze dried. The Oscars are the type of fish which feed on live fish.

These are the types of fishes which feed on both plants and meat. These include goldfish, catfish etc. These fishes also eat pellets and flakes.

These are the fishes which are complete vegetarians by nature. Plecos, Silver dollars, Pacus are some of the fishes which are herbivores and can be raised in the aquarium. These depend on the flake foods and also the algae, which is present in water. You can also provide these fishes with fresh lettuce, spinach, green peas. The green peas should be made into the size of the flakes or pellets for easy swallowing so that it does not cause constipation issues in the fish.

The young cat fishes eat very less. But the male catfish helps in guarding the eggs and newly hatched fry to make sure that they are strong enough to search for their own food. Before they grow and reach the stage of maturity, they only search and hunt for foods which can be easily caught and consumed. So, they hunt for worms or invertebrates. Moreover, they mostly eat hellgrammites, insect larvae, small cray fish etc.

Accumulated gases in the fish tank should be cleared by providing proper aeration and this method is called stripping. Respiration of fish produces carbon dioxide and bacteria in the biofilter produces nitrogen, both of these are the harmful to the growth of the fish. If it is a saltwater tank, then there is a chance of hydrogen sulphide production, which is equally toxic to the fish. Supplying air into the tanks can drive the gases away through turbulence. A trickling filter system is often used for this process. When water is made to flush down from the top of the filter through the plastic media stacked in a column it increases turbulence and contact which helps in stripping the gases.

Providing oxygen supply to the water in the tanks is called aeration. Warm and cool water recirculating systems need 6 and 8 ppm of oxygen respectively for bacteria and fish to survive. RAS tanks which have high load carrying capacity should be able to replace oxygen every 20 and 30 minutes. There should be proper and regular supply of oxygen otherwise it could lead to loss of fish and also there should be a backup arrangement for large recirculating systems. Blowing air through a submerged air stone is the commonly used method to aerate the tank. For one pound of food supplied to the fish, the amount of air required is around 187 lpm/kg/day approximately. Diffuser hose and airlifts are devices used for the aeration process. When aeration is provided sufficiently then there is no need for a distinct carbon dioxide stripping unit.

The presence of waste in the tank increases the demands for oxygen and decreases the amount of dissolved oxygen content in water, thereby lowering the density of fish in the tank. A sump or a clarifier tank is used to collect the excess waste at a slow rate. The main idea of the sump is to collect and sediment all the solid waste which could otherwise the block the biofilter and use up the oxygen. This is isolated from a fish tank and should be periodically cleared. The shape of the sump should be ‘v’, so as to facilitate for easy cleaning.

The two major categories of biofilters are submerged bed filters, which need aeration before and after the water passes through them. Emerged bed filters which have constant oxygen supply to support the process and these are of two types namely Trickling filters and rotating biological contractors.

This is the most important component of RAS because it helps in removing the fine pollutants from water during waste treatment. The media within the filter is made up of materials like plastic sheets, beads, lava rock, gravel or sand grains. The properties of the media should be such that it should have a high surface area for bacterial growth, pores of movement of water, clog resistant and should be easy to clean.

A simple biofilter can be a wheel, barrel or box filled with media on which nitrifying bacteria grow. It can be made of plastic, wood, glass, metal or concrete. The size of the biofilter defines the fish carrying capacity of the entire system. The surface area of the filter should be large so as to accommodate high- density bacteria to process loads of waste present in the fish tank. While designing biofilters the surface areas, ammonia loading and hydraulic loading should be properly estimated.

A practical way of removing the waste from the fish tank is possible through mechanical filtration. Modern recirculating system have an outlet with a filter called the microscreen of mesh size 40 to 100 microns. The presence of the micro screen has some advantage such as it reduced the load on biofilter, removes the organic impurities, improves and facilitates the biofiltration process. The type of micro screen used is called a drum filter and has the following functions: Filters the elements present in the water. The elements are pushed to the backwash area by the rotation of the drum. The solid waste is removed into the sludge tray by spraying water on the filter. The sludge is removed with water from the tank and is sent to external waste treatment.