1. Introduction
Steelhead salmon (Oncorhynchus mykiss) is a pacific salmon species, distributed in the northeastern part of the Pacific. Oncorhynchus mykiss is commonly known to the general public also as Rainbow trout, even though it is a salmon.
In the wild, spawning and hatching occur in freshwater, and when Steelhead parr reached 1-3 years, they may migrate into seawater. Later, after maturation has been completed, they will then return into freshwater to spawn. Mature fish will spawn up to 3 times if they survive long enough. They can reach sizes, up to 14kg or more, however 8-9 kg is more common.
Steelhead is an anadromous fish whose life cycle is similar to Atlantic salmon. But while the Atlantic salmon normally migrates to marine water during the first or second year, and later migrates back to freshwater to spawn, Steelhead salmon, can either stay in freshwater through its entire lifecycle, or, such as Atlantic salmon, can migrate to brackish water or seawater, and later migrate back into freshwater to spawn like Atlantic salmon.
The name steelhead comes from the colors that the fish develops when migrating to seawater and the name rainbow trout comes from the colors it has while still in freshwater.
The Steelhead species thrives at higher temperatures compared to Atlantic salmon and does not tolerate high salinities at low temperatures.
Steelhead has been farmed for more than 200 years and therefore is now well domesticated. By genetic selection, it has become a fast-growing robust fish, resistant to many of the diseases encountered in salmonid farming.
The fish performs well at temperatures up to 20°C, as long as water exchange and water chemical conditions in general are optimal. It can survive temperatures up to 27°C. Optimal farming temperature in open systems is in the range of 15°C, while in RAS systems, where all parameters can be maintained more consistently, the fish will thrive at an optimal production temperature of 17-18°C.
The end-product from Steelhead farmed in seawater is very different compared to the end-product coming from Rainbow trout farmed in freshwater. This is reflected in the selling price where Steelhead reaches prices 2-4 times higher than Rainbow trout, which is close to the selling price of Atlantic salmon.
2. Key notes for when considering farming Steelhead Salmon
- In general:
i. The quality of the meat from the fish raised in seawater is potentially the best of any of the salmon species. It has a firmer and more delicate texture compared to Atlantic Salmon. Only the seawater farmed fish sells at a high price.
ii. The yield of Steelhead, both head-on-gutted (HOG) and fillet with skin on, is slightly higher compared to Atlantic Salmon. (More product to sell per kg fish produced).
iii. Due to the lack of tolerance to salinity at low temperatures, offshore sites for cage farming are limited. Most fish farmed in seawater are in fact farmed in estuaries with salinities between 10 and 20 ppt. and / or only left in the cages during the summer season.
iv. The fish coming from seawater can substitute Atlantic salmon, as the filet is very similar, the products from Steelhead can tap into this large and well-established market with a premium product. In addition, it can have its own premium market, as some countries prefer Steelhead over Atlantic salmon. Steelhead salmon is especially favored for the Sushi market.
v. In Japan the market has been developed more than any other farmed species. And it is possible to tap into this large and well-established market. This is largely made possible by the extensive experience and knowledge in producing this species; and that demand still exceeds production.
vi. The supply chain of eggs is well developed, and supplies are available year-round from a number of suppliers. (In-house production is not very complicated either).
vii. The technology used in all phases of the trout farming process is well-proven, both in open flow through installations as well as in RAS.
viii. Steelhead Salmon has a high resistance to diseases. This species has been domesticated over the past two centuries and has become a fast-growing robust fish immune to several of the diseases which commonly threaten fish farm production.
ix. Steelhead's skin and scales are less sensitive, making it easier to handle and more resistant to scratches than Atlantic salmon.
x. The early life cycle of Steelhead salmon is simpler than Atlantic salmon. Steelhead salmon does not require the same stages. For instance, the time required for smoltification is almost as low as half that of Atlantic salmon. In addition, Steelhead salmon is more flexible on how and when it is introduced to seawater. However, Steelhead salmon should preferably have a minimum size of 200 grams before transfer to seawater.
xi. Eco-pollution from farmed salmon and issues related to sea lice are major concerns in cage farming. In some cases, sea lice are dealt with by introducing fish into the cages that prey on them. However, chemical treatments are still used in many places, which have considerable impact on marine life around the cages.
xii. Steelhead is a very aggressive feeder, making feeding practices easier and allowing high assimilation of feed to saturation on all individuals. On the contrary, Atlantic salmon is a very shy fish, which hardly allows people around the tank while feeding, thus making it harder to monitor feed assimilation of each individual.
xiii. Due to the shape of the fish, it is possible to make more expensive cuts out of a smaller Steelhead salmon. This means that from a 3-4kg Steelhead salmon, similar cuts can be made as from a 4-5kg Atlantic salmon.
- In relation to RAS farming of Steelhead Salmon:
i. Portion size fish of Steelhead salmon and fish produced in freshwater have relatively little value, too low to justify and support investment in a RAS. Therefore, only production of big fish + 3000 grams in seawater is of relevance for RAS farming of this species.
ii. As listed above, the fillet of Steelhead salmon is thicker than Atlantic Salmon, therefore, attractive cuttings can be made from a 3,5 kg Steelhead salmon. This is even more pronounced in fast growing Steelhead salmon produced in RAS systems which tend to have even thicker fillets than Steelhead salmon produced under less optimal conditions. Harvesting the fish at a smaller size will reduce the production costs.
iii. Steelhead salmon can be raised in high density RAS culture, up to +200 kg/m3, even up to +300 kg/m3 (Portion size fish), as long as water quality is optimal throughout the tank.
iv. The Steelhead salmon species performs well at 17-18 °C, even up to 20 °C in RAS farms. Thereby also the biofilters can perform very well and efficiently for production of Steelhead in RAS.
v. A grow out facility for Atlantic salmon would be roughly 50 % bigger in size and cost compared to a facility for the production of Steelhead salmon. This is due to the higher density at which Steelhead salmon can be farmed, and the higher water temperature which makes the biofilters in a RAS facility for Steelhead salmon work roughly 50% more efficiently.
vi. Production of Steelhead salmon juveniles / smolt is simple and does not require a dark phase like for Atlantic salmon. Furthermore, smoltification time can be reduced by approx. 50%, resulting in quite modest investments on facilities for smolt production compared to the required installations for Atlantic salmon.
vii. Steelhead salmon's skin and scales are less sensitive, making it easier to handle than Atlantic salmon. And Steelhead salmon are in general very robust in comparison to Atlantic salmon and are therefore easier to handle in an industrialized RAS setup.
viii. With advanced RAS technology in combination with wastewater treatment technology, Steelhead salmon can be produced without causing the environmental problems associated with cage farming. This presents an opportunity to expand Steelhead salmon production beyond the limitations set by suitable sites for cage farming.
ix. The flesh quality of Steelhead salmon depends a lot on the swimming activity of the fish. In RAS farms, when considering fish biology/behavior, it is possible to tailor design the system in a way that optimizes the water velocity/swimming activity relationship. The latter will allow the fish to notably increase the buildup of proteins instead of fats, which improves both the taste and the texture of the filet. In this regard, it might be possible to develop a premium market for this species. The water velocity within the tank should be 0,5-1 body length per second.
x. In RAS farms Steelhead salmon can be produced 100 % free of parasites. In this regard, it might be possible to develop a premium fish for the sushi market.
xi. Steelhead's growth performance in a Recirculating Aquaculture System (RAS) is optimal at temperatures of 17-18°C, still good at 20°C, and can survive up to 27°C. In comparison, the temperature for optimal growth in Atlantic salmon should not exceed 14°C. A production temperature of approx. 18°C is fine for RAS technology. Biofilters perform better at higher temperatures. For instance, the overall biofilter capacity would be reduced by 30-40% if the temperature decreases from 18°C to 12°C (Optimal for Atlantic Salmon).
3. Biology
There are two main production phases to produce high value Steelhead salmon: the freshwater phase and the seawater phase.
The production of Steelhead salmon from eggs into a 200 grams smolt in freshwater does, unlike Atlantic Salmon, only require two stages: the hatchery and the nursery stage. However, for optimizing production logistics, the process might well be phased into 4-5 stages. This facilitates the supply of a steady year-round flow of fish into the growout facility.
The production of 200 grams smolt could, for example, be split into the following five stages:
- Egg stage.
- Start Feeding stage.
- Fry stage.
- Juvenile stage.
- Smolt stage.
It all depends on the overall logistical plan specifically designed for the production site and total production volume for an optimal production strategy.
i. Nursery:
Steelhead Salmon juvenile, feeding behavior in Ras tank, (video from Bent Urup)
ii. Harvest:Fast grower Steelhead Salmon, reaching 5kg in the RAS2020 system.
Picture of a fast grower Steelhead Salmon that reached 5kg (picture from Bent Urup).