RASTECH Magazine

Fresh Tips: So many strains, so little time

October 26, 2021  By From the experts at the Freshwater Institute

Eyed eggs beginning to hatch. Photo: The Conservation Fund Freshwater Institute

Maintaining broodstock to vertically integrate the source of fish eggs is not always feasible for new or smaller-scale recirculating aquaculture system (RAS) farms. As a result, these RAS farms are reliant on egg or fingerling suppliers to keep facilities stocked and production plans on schedule. RAS producers should familiarize themselves with suppliers and potential strains when evaluating fish stock selection, as there are many strains available with a wide range of attributes.

RAS operators should always opt for specific pathogen free (SPF) certified producers when choosing an egg of fingerling supplier. Suppliers should be able to provide SPF certification documents for review. Consider suppliers with a strong reputation and history of successfully supplying the industry. If the supplier is relatively new, ask for customer contact information and follow-up to complete due diligence. Suppliers should be able to answer your questions about available fish strains and growth potential, as well as general questions about their on-farm biosecurity practices and general egg incubation or initial fish acclimation recommendations.

Location of the supplier in relation to the RAS facility can also be an important factor when selecting a fingerling supplier. RAS facilities planning to rely on fingerling fish may need to identify suppliers within range where fish can be delivered or picked-up and hauled safely in a single day. Location is less important when selecting an egg supplier. Eyed eggs are easily shipped in insulated boxes around the world. However, selecting a domestic egg supplier may alleviate some of the extra challenges associated with importation, such as paperwork and inspection by customs agencies, which is required with international shipping.


RAS facility bioplanning provides an estimate of how many eggs or fingerlings will be needed to meet production goals. Operators should select a supplier or combination of suppliers to create the egg or fingerling supply to meet the farm bioplan. RAS facilities must also identify suppliers whose availability is compatible with the bioplan. Those RAS facilities receiving eggs or fish more frequently may grow smaller cohorts of fish, while those receiving only seasonal shipments may need to ‘cold bank’ portions of larger cohorts to stagger harvest schedules and provide consistent product to customers. RAS facilities with multi-phase construction or expansion plans should communicate future plans to suppliers to allow them to increase their capacity to meet the needs of future growth.

Farm goals and strain attributes
Fish strains with faster growth rates will generally be more profitable for RAS facilities. As a result, growth rate is a primary trait for selective breeding programs. However, there is variation in the growth rate of commercially available strains, making strain selection important for producers. In addition to growth rate, several secondary attributes with genetic components may be of importance to RAS producers. For example, strains with better genetics for disease resistance, improved fillet yield, or low rates of early maturation may be preferred when growth potential is similar. In some cases, sacrificing some growth potential for preferred secondary attributes may be advantageous.

Monosex and ploidy
Manipulations to produce monosex or triploid fish can also provide advantages for RAS producers. Many tilapia farmers grow all-male populations of fish for improved growth rate while all-female salmon populations are becoming popular to eliminate early male maturation. Additionally, sterile triploid salmon further protect against or eliminate early maturation. However, triploid fish can require specific husbandry conditions and dietary requirements that are not well defined, resulting in reduced growth rates compared to diploid counterparts at larger sizes.

RAS operators should maintain detailed records of supplier and fish strain growth, survival, deformity and downgrade rates, and other important performance metrics. Past data can be used to track performance through the years, identify trends in fish performance by breeding season, or compare strains to inform future selections. Thoughtful, data-based decision making will ensure an adequate supply of fish that perform well and meet the unique end goals of each RAS producer. Developing a good relationship with egg and fingerling suppliers will keep you engaged in the latest improvements through selective breeding, availability of new offerings, and open a discussion for feedback and optimal selection of strains.  

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