Some sites will fix inflows strategically along the length of the raceway with the aim of pushing waste along to the end with the extra current. Self-cleaning of the tank bottom isn’t as thorough as in a circular tank and waste feed and feces can accumulate on the bottom. Flow must be maintained to provide acceptable water quality at the end of the raceway or trough, where the water quality is poorest, not just the head or middle sections.įarmers overcome this shortcoming by injecting oxygenated water at different points along the raceway to boost the water quality, or use air stones to inject oxygen straight into the water. Because of the long nature of the raceways, water quality degrades the further the water travels from the inflow. ![]() Spin rate is not a consideration as the water velocity is determined by the flow rate going through the raceway.ĭead zones are generally non-existent in raceways and troughs but there are water quality considerations regarding flow. Flow rate is still equally important and provides necessary turnover. Though not set up the same as circular tanks, long tanks like raceways and troughs still have the same considerations of flow to maximize water quality. ![]() Horizontal spray bars can also be added to the inflow depending on application. This ensures the entire water column is moving evenly. Inflows should be set up with vertical spray bars to ensure water is injected throughout the water column and to ensure dissolved oxygen in the line is not lost to the atmosphere before it is exposed to the water. If there are two inflows, try to keep their angles even so they are working together. Pointing the inflow towards the center of the tank will create short circuiting.Īiming the inflows at the tank wall at 45 degrees is a good starting place when setting the spin. Inflow should be aimed at the tank wall to ensure the best “push” around the outside of the tank. Generally, short circuiting occurs when the inflow(s) are not angled properly, which is more common in tanks with more than one inflow pipe. The vortex over the drain can be seen to migrate around the center drain instead of being fixed over top. When this happens, usually one will see oxygen decrease drastically in the tank, fish distribution will not be uniform and solid waste begins to accumulate. ![]() No longer is water travelling a nice circle, the water pattern is erratic and not uniform.Ĭertain parts of the tank will develop dead spots where the water doesn’t mix. Tank spin shouldn’t make the fish struggle against the current but allow them to keep station easily.Ī tank is known to short circuit when its spin rate is set poorly, and the whirlpool water pattern breaks down. For trout and salmon, about 1.5 fish lengths per second is a good starting point but fish observation is essential. The overall effect is good distribution of fish within the tank and even conditions throughout.Ĭhoosing the right spin is a matter of observation. The spinning effect provides fish with current and can be adjusted by moving the inflow water angle.įor trout or salmon, fish will point themselves into the current (spin) and, when at rest, each fish will have its own little space in the school. Spin rate does not affect the rate at which water enters or exits the tank, it is only how fast the water is traveling around. The rate at which the water travels in a circle within the tank is known as spin rate. (5,000 liters/60 minutes = 83.3 L/min) Thus, a 5,000-liter tank requires flow rate to be set at 83.3 L/min to provide one turnover each hour. Turnover rate is specific to the species being reared and rearing density, but one turnover per hour is a good place to start for many species.įor example: a 5,000-liter tank of trout requires a turnover rate of one hour. Turnover rate is how long it takes to replace the entire volume of a fish unit. Usually expressed as L/min or ft3/sec, tank flow rate is determined by the desired turnover rate. If the flow rate is too low, fish health will quickly suffer.įlow rate must be high enough to keep ammonia and CO2 levels from accumulating. ![]() Flow rate is the amount of water that flows into a tank over time that is, how fast water is coming into the tank. The most important aspect of water flow to the fish farmer is flow rate. It also distributes oxygen throughout the water column and should provide water conditions specific to the species being reared. Water moving through the tank provides self-cleaning, flushing away solid and dissolved waste products. The way water moves into, within and out of tanks and rearing areas is a subtle but essential consideration for fish husbandry.
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