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Fresh Tips: The art of RAS feeding

June 9, 2020  By From the experts at the Freshwater Institute

A malfunctioning feeder damaging pellets and preventing proper feeding rate

Feed is the primary cost of RAS production. Accordingly, proper delivery of high-quality diets is one of the most important aspects of fish culture for maximizing fish growth and overall efficiency.

Selecting feed
Fish feed should be a complete diet providing all necessary nutrients for the species being raised and the corresponding life stage. It should be made up of high-quality digestible ingredients.

Additionally, the RAS environment demands feed that maintains its structural integrity in water and yields intact fecal matter that is easily removed by mechanical filtration unit processes. A slow-sinking feed pellet will be more easily removed through drains and settling structures than floating feeds. Feed should be elevated from the floor and stored in a dark, temperature-controlled (<60 °F) and humidity-controlled (<6 percent) area and used in a first in, first out scheme.


Dispersing strategy
Positioning of stationary, automatic feeders around culture tanks should be carefully considered. Water currents will carry slow-sinking feed pellets a short distance as they sink, so avoid placing feeders adjacent to side wall drains where feed pellets could leave the tank too quickly.

If using multiple feeders, they should be placed at different locations around the tank to expand the area of feeding as much as possible. Observe the rate that feed is dropped into the water by feeders. An excessively fast feeding rate could mean feed sinks to the bottom of the tank too fast for fish to capture all the pellets. In this case, equip feeders with spreaders to broadcast feed over a larger area and provide more opportunity for fish feeding. Position and adjust the spreader so feed is not being thrown outside of the tank or being cracked or damaged.

When hand feeding, be sure to throw feed to all areas of the tank in amounts small enough that each scoop of feed is consumed before reaching the bottom of the tank. Try using smaller scoops or spreading feeding over more time to deliver an appropriate feeding rate as needed.

Setting up feeders
Use manufacturer-specific feeding charts or historic farm data as a starting ration that can be adjusted to reach satiation over time. Reprogram feeder controls any time changes are made to the speed of the feeder delivery or the feed pellet size. Adjust programmed ration whenever additional fish are stocked or removed from the tank. Ration on a percent body weight basis and number of feeding events per day will decrease as fish grow. However, at least eight to 12 evenly spaced feeding events per day are recommended to prevent spikes in ammonia and carbon dioxide production and oxygen consumption in RAS systems. This will smooth the water quality profiles in the RAS over a 24-hour period.

Achieving satiation
Underfed fish will not grow as quickly and can injure other fish and damage fins with aggressive behavior, while overfeeding will result in wasted feed and money.

The first step to achieving satiation is being familiar with the feeding behavior of the fish species and lifestage. Take time each day to observe how the fish behave during a scheduled feeding event and adjust the programmed ration if fish are feeding over-aggressively or passing up feed pellets.

Additionally, monitor for spitting, head shaking, or gill flaring behavior that may indicate feed is unpalatable or pellet size is too large for consumption. Culture tanks with proper hydrodynamics will remove uneaten feed pellets through the bottom center drain.

If the bottom center drain flow is accessible, a collection basket can be placed in the flow during a feeding event and removed a few minutes after to monitor if any feed is being wasted, and if so, exactly how much. Consider increasing or decreasing the programmed ration if there is no or excessive wasted feed in the bottom center drain flow.

A well-placed underwater camera could also be used to observe wasted feed leaving the bottom center drain of the tank.

Items to monitor
During daily checks, confirm feed hoppers are filled and feeding rate appears normal. This can be done by observing a feeding event or comparing the amount of feed left in the feed hopper from the day before.

Confirm that spreader equipment is working and positioned correctly. Regularly check that feeders or spreaders are not damaging feed pellets. This will be apparent if excessive fines are accumulating on or around the feeding equipment.

Damaged feed pellets can create a reservoir for bacteria and mold, create water quality problems, and waste money. Routinely clean feeders, spreaders, and hoppers. Maintain an inventory of critical spare parts or a complete spare feeder, especially if lead times from international suppliers are long, to keep the fish properly fed and on pace for production goals.

Several days of underfeeding will negatively impact growth, fish health, and the farm’s bottom line.

For more information visit, FreshwaterInstitute.org.

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