You are here

Sustainable Fisheries

Aquaculture System Overview:Tilapia Recirculating System (RAS)


Like any agriculture production system, tilapia recirculating systems require inputs including capital, land, and water resources.  They also require development of output markets that have been thoroughly sourced and researched.  Identifying and evaluating output market demand with respect to product quantity and product characteristics is a critical element of aquaculture financial planning.  A “MARKET FIRST” approach can help investors maximize aquaculture business opportunities by developing an integrated business plan that matches production resources, species, and systems with output market requirements.

Organism: Tilapia

Tilapia is a fast-growing species. Optimum temperature is 80℉ and lethal maximum and minimum temperatures are 107℉ and 53℉, respectively. Growth and reproduction will generally start at temperatures above 75℉ although some reports indicate growth above 60℉. Tilapia typically tolerate a relatively wide range of water quality in terms of hardness, alkalinity and pH as well as low levels of salinity. The fish will endure dissolved oxygen levels below 2 ppm. Fish will be severely stressed at levels below 1 ppm with mortality ultimately occurring. Oxygen levels of 4-5 ppm are best for growth.

Harvest size is generally at an individual weight of 1-2 pounds (450-900 g). However, some markets may seek small individuals. Frequently larger sizes are filleted while smaller sizes are either sold in the round or gilled and gutted. Production cycle (growing time) will vary greatly according to temperature but, at acceptable temperatures, it often takes eight months or more to produce a 1.5-1.7-pound (700-800 g) fish.

Tilapia do not have a true stomach and therefore need to be fed several times a day or the unit needs to use demand feeders. Grow-out units are often fed with feed with a protein content ranging from 32-36%. Fish in nursery units and other juvenile life stages require higher protein content (e.g., 40-55%). Feeds will generally be floating or slow sinking. Pellet size will depend on the age of the fish being fed. Juvenile diets range in size from #0 to #4 crumbles. Pellets for grow-out range from ⅛ to ¼ inch. Feed efficiency will also vary with temperature, water quality and the age of the fish, but for grow-out, a feed conversion ratio (FCR) of 1.6 can be considered as suitable--some operations getting even better conversion rates. Density for grow-out in recirculating tanks typically range from 0.5-1.0 pounds/gallon.

Production Methods: Recirculating Systems (RAS)

RAS reuse the same water to grow the crop of fish. The water is circulated through filters to remove wastes. Oxygen may also be added to ensure satisfactory dissolved oxygen levels. As the water circulates new, or “make up” water will be added to replace water lost by evaporation as well as to dilute any dissolved wastes not removed by filtration. In extreme cases, more than 50% of the system’s water volume may be replaced daily with systems with low-level filtration replacing roughly 30% per day. However, most modern units with efficient filtration replace 5-15% per day.

Recirculating systems are often enclosed in a building with a concrete slab or a gravel floor; gravel allowing more flexibility to move tanks and other structures as the operation evolves. Tanks may be fiberglass, plastic, stainless-steel, concrete or concrete block, or even wood with impermeable liners. Ideally, the size of grow-out tank needs to be linked to the marketing strategy such that one tank is harvested over a relatively brief period to satisfy market demand. If much of the fish handling is to be done manually, the tanks need to be constructed/installed so that nets and other tools can be conveniently used. Space is important and it is necessary to be able to have easy access to all the facilities.

While there are many variations, a typical production strategy would be to start with a 0.04 ounce fry (1-2 g) and grow these in a nursery tank for 60 days at a density of 6 fish per gallon, harvesting when the fish are 0.7 ounces (20 g) and then transferring these fish into grow-out tanks at a rate of 0.4 fish per gallon and growing them for roughly 180 days to an average weight of 1.8 pounds (800 g) at a total density of 0.75 pounds per gallon.

Unique to Oregon

For tilapia, temperature is a crucial factor. Seasonal temperatures at the farm site are important.  Tilapia nearly always require temperatures above normal ambient external conditions and tank water must be heated, necessitating energy costs. One option could be to use a site with access to geothermal energy. There may be other shuttered industrial sites that could provide other resources for developing into an aquaculture enterprise.

For land use, aquaculture is a conditional use, and it is necessary to check with local and state authorities. Similar homework is necessary regarding water use. The interface for land and water is the watershed; both at the local and basin levels.

For operators purchasing tilapia seed, hatcheries are available both in- and out-of-state (seed suppliers). For out-of-state purchases, there will likely be additional regulations.

Tilapia feeds can be purchased from several mills (feed mills). In the event specific tilapia diets are not available, tilapia’s broad dietary habits would allow a producer to use other fish feeds, although these might not yield optimal results as they could cost more or result in slightly slower growth since not tailored specifically for tilapia.

Selected references:

Authored by John Moehl (2021)