Aquaculture Feeding Practices for Recirculating Aquaculture Selecting the proper feeds and feeding methods is an important aspect of fish growth. Feed considerations are therefore a fundamental part of indoor recirculating aquaculture. Unlike pond culture, the only source of nutrition for aquaculture fish is in the feed they are given. Complete fish feed pellets, which contain all necessary nutrition, are essential. Feed ingredients are chosen for their digestibility of protein, fat, and carbohydrate components, as well as their buoyancy characteristics and price and accessibility for feed mills. Most of these complete feeds Hand feeding tilapia contain fish meal, which provides the proper amino acid profile and healthy omega-3 fatty acids needed for fish nutrition. Sustainability of aquaculture, however, will require feeds that reduce the fish meal needed, decreasing ocean of the water. Shellfish species like which is particularly useful in species fishing pressure in the name of aqua- shrimp and crayfish need a sinking like bluegill. culture. Replacing fish meal with other feed because they spend the majority proteins can negatively change the of their time on the bottom. It is much Carnivorous v. Omnivorous fatty acid profile from heart-healthy more difficult to gauge whether or Diets – Fish that are carnivorous omega-3 fatty acids to saturated fats not the shellfish are consuming the require more fish meal and a higher and trans fats, making fish products feed rationed to them, and over- or percentage of protein in their diets less healthy for human consumption. under-feeding is common. For sinking than herbivorous fish that can directly Thus feed ingredients must be careful- feeds, feeding behavior can be mon- feed on vegetative matter. Omnivo- ly selected. itored to some extent by designating rous fish, such as tilapia and channel a feeding area in the tank and netting catfish, can grow well on both animal FEED OPTIONS the bottom in that area approximately and plant protein. Floating v. Sinking Feeds – 15 minutes after feeding to gauge the Floating feed is commonly used in amount of uneaten feed. Semi-floating Medicated Feed – When fish get a the production of finfish in order to or slow-sinking feeds can be used bacterial infection, one of the most ef- monitor feeding behavior. The un- for finfish that are shy feeders, or fective treatment options is to provide eaten pellets can be easily netted out fish that won’t feed from the surface, medicated feed so that antibiotics get FA 0002A December 2014 Aquaculture inside the fish’s body. Because sick fish not contain all the nutrition fish need toms such as skin lesions or erratic do not eat, it can be difficult to ad- to grow optimally. Complete feeds are swimming behavior, will not eat feed. minister medicated feeds. Garlic oil is those that contain all the vitamins, Withholding feed will help avoid a commonly used feed attractant that minerals, amino acids, fatty acids, water quality issues and mortalities. can be used to topcoat the feed and and other components required by improve fish uptake. Medicated feed the fish to grow. Complete feeds may Feeding Response – The feeding should be stored in a separate location be used exclusively, but these feeds response is the amount of vigor that from other feeds, and it is typically are typically more expensive. fish display in consuming feed. If fish refrigerated to prolong its life. are slow to eat and leave feed floating The feed production process and on the surface of the water, feeding Medications for food fish are strictly ingredients used determine the struc- should cease and the uneaten feed controlled and a farmer must work tural stability and nutritional quality should be removed from the water. with an aquatic veterinarian to obtain of the feed. Pellet mills compress feeds If the fish are feeding very aggressively a prescription to purchase and use into a dense pellet that will sink and and consume the feed quickly, more medicated feed. The prescription will may be more prone to crumbling, feed should be added. Feeding should include an application rate, amount which creates more fine particles that continue until the fish cease eating and to be fed, and duration to be fed. The the fish cannot eat. This could cause leave a small amount of feed floating. prescription should be strictly adhered water quality issues. Extruded feeds Excess feed should still be removed. to, preventing further harm to the fish can be produced under heat and or the biofilter. Approved aquaculture steam that cause starches to expand, Feeding to Satiation – Satiation is drug additives for feed include Terra- creating a structurally sound feed the point at which fish are full and do mycin, Romet, Aquaflor, and others. that will float. Feeds that are small in not desire to eat anything more. The A withdrawal period (i.e., time between diameter or have low carbohydrate typical method for gauging satiation the end of the treatment and harvest (starch) content will tend to sink. in fish is to feed the fish as much feed of the fish), is required for food fish as they will consume in 15 minutes. to ensure that the antibiotics do not FEEDING PRACTICES Feeding should start in small incre- transfer to humans. This period varies Fish should not be fed if the water ments to determine how aggressively depending on the drug used. quality in the system is not adequate the fish are feeding. If they are feeding or if fish are sick and stressed. Fish vigorously, then more feed should Feed Quality – Fish feeds range in will not eat when they are stressed and be added until the feeding behavior terms of their ability to provide ade- extra feed in the water can cause water slows. Cease feeding if feed is left quate nutrition for the fish. Less ex- quality issues. Feeding should be uneaten, and remove excess feed after pensive feeds that may be a byproduct avoided when dissolved oxygen is low the 15-minute feeding period. The of another agricultural process can be or ammonia levels are high. Sick and amount of feed fed and the feeding useful as a supplemental feed but will stressed fish, recognizable by symp- response should be recorded to help predict the amount of feed the fish will require in the future. FEED CALCULATIONS Feeding Schedules – A feeding schedule is a prediction of the amount of feed that should be fed to the fish at any given point during the growth cycle. It is based on a percentage of the total biomass, or the combined weight of all fish in the system. Smaller fish require a higher percentage of their biomass in feed on a daily basis than 2.5 mm floating feed Feed fines larger fish. A typical feed schedule may call for a feed ration 2 Aquaculture benefit to the fish. Small feed particles, the fines, will also not be consumed by fish and will create water quality issues. Fines stain the water dark col- ors and contribute to high biological and chemical oxygen demands. Good quality feed that holds together in the bag and in water will cause fewer issues with water chemistry because the fish can more easily consume the Juvenile tilapia feed and feed particles can more easily be netted or filtered out of the system. It is important to purchase high that equals 40% of the fish biomass Accurate feed records and fish weight quality feed from a reputable supplier. on a daily basis as fry or juveniles, data must be collected to calculate Choosing a high quality, water-stable then 10% of biomass as fingerlings, FCR. These values are important for feed that is free of fines, easily digest- then 2% - 3% of the fish biomass as gauging production efficiency and ible, and nutritious is important. It is adults. A daily growth increment improving production practices over then helpful to feed in small amounts should additionally be considered in time among species, cohorts, and on a frequent basis (3- to 5-times per the biomass estimate between sam- systems. Since feed costs are a consid- day) and utilizing the correct size of plings. Depending on the species, erable portion of production costs feed as well as a feed delivery system fish generally add more weight per (40% - 60%), even a slight improve- that removes fines from the system day as they grow. For example, a fish ment in feeding efficiency can yield before they can enter the water. may grow by 0.1 g (larval) to 2.0 g large changes in profitability. (fingerling) to 10.0 g (adult) per day Effects on Population Growth if optimal water conditions are met. IMPLICATIONS OF FEEDING Rate – Feeding smaller rations and The daily feed ration should be split Feed Effects on Water Quality – feeding more frequently can reduce into multiple feedings per day to avoid Feed contains protein utilized by fish the ammonia and oxygen stress on the water quality issues and to improve to build muscle, but the protein also system. However, providing enough feeding efficiency; 3 to 5 feedings per creates nitrogen waste in the form of feed in a single feeding to ensure day is common. ammonia excreted through fish gills that all the fish have access to feed is + critical for even fish growth. Finding and feces. Ammonia (NH3 or NH4 ) Feed Conversion Ratio – Feed can be extremely toxic to fish and it a balance between these strategies will conversion ratio (FCR) is a common must be removed from the system as optimize feeding efficiency. term in aquaculture that provides quickly as possible. One method to do a standard to compare the feeding this is bacterial processing to nitrite Aggressive fish can consume more - feed and grow at a faster rate than efficiency of different species, feeds, (NO2 ), which also can be toxic, but and systems.