Density and growth
Density is a measure of the mass of fish per volume of tank space, usually in the units of (kg/m3). In nature charr can be seen in great shoals and one of the main assets/advantages of charr in farming is its adaptability to great density. Maximum density in charr farming depends on environmental factors such as water flow and temperature, which affect the maximum amount of available oxygen.The type of tanks also seems important, especially in regard of current and water exchange.
As the charr grows it seems to appreciate and thrive in great density.It is not unusual that density at ongrowing is 60-80 kg/m3 and there are many examples of good growth at twice that density.Better growth has actually been measured in farming at 50 kg/m3 than at 15 kg/m3. The explanation is probably change in behaviour, less strife and aggression at greater density as mentioned earlier. It is noteworthy that in spite of the great density, the fish is looking fine, without bite marks or wounds on the skin and fins.
In farming it is very important to make the most efficient use of the farming space and therefore the density of fish per farming unit or tank is of vital importance. This is especially significant, when farming in tanks where the volume unit is expensive when compared to farming in e.g. cages or ponds. The volume often becomes a limiting factor in the production capacity.
Density of charr in tanks can be very great without affecting growth negatively. It is common that the density is kept at 50-100 kg/m3 or more without trouble. Usually smaller fish are kept at less density than larger. It may therefore be convenient to start with fry at 30-50 kg/m3 and then let the density increase with the growth of the fish.If the tank is large, the initial density may be adjusted by setting the water level low at the beginning, slowly increasing it as the fish grows. If the density initially is low (less than 20 kg/m3), the size variability may possibly be kept at bay by feeding in the dark. The fight over feed and territory may be less in the dark then in daylight.
At increased density the oxygen use increases and measures to ensure a suitable content of available oxygen must be taken, e.g. by increasing the water flow. The water requirement can become great, especially if the farming temperature is high. The carrying capacity of water supply piping and outflow ducts must be adequate and should be accounted for already at the designing stage. There is also the possibility of direct oxygenation or tank aeration of the water, maintaining a constant flow.
With the option of increased water flow, it must be seen to that the current is not too great. Probably the current can be decreased a bit, as the fish takes partly care of the cleaning of the tank (hvað er átt við? HÞ). At a very high density, the strain on the farming system and the fish is increased and the risk of the operation with it. The water quality may not be limiting for the fish's growth. When the density is very high, the water requirements may reach a level beyond the limits of the tank space. If the carrying capacity of the outlet system is limiting to the flow, the water amount in the tank becomes irregular or fluctuating and may start to flow over the sides. If the flow has to be reduced or if the flow is limiting, it is necessary to be able to add oxygen to the system to satisfy the needs of the biomass in the tanks.
In the production plans, one should aim for the water flow and oxygen supply to be fully utilized and the density at maximum when the fish is reaching slaughter size. That way the production capacity of the farm is brought to full use. In a stressful environment, the risks of disease outbreaks in the herd are increased. It is hard to keep track of losses and the keeping of the fish at great density, especially in large and deep tanks.
--------------------------------------------------------------------------------
2006-08-25 05:14:57
·
answer #1
·
answered by kmday1130 3
·
0⤊
0⤋
Well you divide the mass of the fish by the volume.
m= mass of fish
v= volume of fish
m/v = density of fish
Now why you need this I'm not sure. Maybe you are asking how many you can put in a tank;-) In which case we'd need to know what sort of fish we are talking about.
2006-08-25 06:12:04
·
answer #2
·
answered by Sabersquirrel 6
·
0⤊
0⤋
Fish density should be one inch of small thin fish per gallon of water. The bigger and fatter the fish, the more water it needs to stay healthy.
2006-08-25 07:54:22
·
answer #3
·
answered by 8 In the corner 6
·
0⤊
0⤋
Most fish have the same density as water. That's why they can swim at any level in water...they intake less or more air into their bodies to lift them to different levels of the ocean/sea/lake/etc.
2006-08-25 05:15:06
·
answer #4
·
answered by Claire 3
·
0⤊
0⤋