Steelheads salmon

1. Introduction

Steelhead salmon (Oncorhynchus mykiss) is a pacific salmon species, distributed in the northern east part of the Pacific. Its culture is not new and has long been favored, both in north America and in Europe.

In the wild, spawning and hatching occur in freshwater, and when Steelhead parr reached 1-3 years, they will migrate into seawater. Later, after maturation has been completed, they will return into freshwater to spawn. Mature fish will spawn up to 3 times if they survive long enough and can reach pretty big sizes, up to 14kg or more, however 8-9 kg is more common. (For more info: Biology section)

Oncorhynchus mykiss is commonly known to the general public whether as Rainbow trout, whose life cycle is in freshwater or Steelhead salmon, an anadromous fish whose life cycle is similar to Atlantic salmon.

2. Culture Systems

  • Advantages of Steelhead salmon VS Atlantic salmon

i. The quality of the meat from the fish raised in seawater, is potentially the best of any of the salmon species. With a firmer and more delicate texture than the Atlantic Salmon.

ii. Higher resistance towards diseases 

iii. High density culture: up to +200 kg/m3 (as long as the water quality is within the optimal range throughout the tank).

iv. Growth performance in RAS: optimal at temperatures of 17-18°C, still good at 20°C, and will survive up to 27°C, whereas the temperature for Atlantic salmon should not exceed 14°C.

v. Skin/scales are less sensitive and therefor takes handling better than Atlantic salmon.

vii. Steelhead is a very aggressive feeder, making feeding practices easier and allowing high assimilation of feed to saturation on all individuals. On the contrary, the Atlantic salmon is a very shy fish, which hardly allows people around the tank while feeding making it harder to monitor feed assimilation of each individual.

viii. Product quality will generally be considered above the one of Atlantic Salmon.

ix. The yield (HOG and Filet skin on) is slightly higher compared to Atlantic Salmon.

x. Due to the shape of the fish, it is possible to make more expensive cuttings out of a smaller fish, meaning that from a 3-4kg Steelhead salmon you can make similar cuttings as from a 4-5kg Atlantic salmon.

  • Disadvantages of Steelhead salmon VS Atlantic salmon

Today, the Atlantic Salmon advantage on the Steelhead salmon is mainly due to the marketing of the Norwegian salmon industry, making it, in general, a more recognized product on the market. Except in a few markets, like in Japan and in the UK, where the quality of the Steelhead salmon has been recognized, especially for the sushi industry as the firmer texture is more attractive. In addition, the layman consumer will find it difficult to observe the difference between the two products, except in a blind testing.

Aqua-Partners verdict is that over time the Atlantic salmon producer will swap into the production of Steelhead salmon, due to consumer recognition and because this fish is more suitable for farming in RAS systems.

3. Biology

  •  Family

Steelhead salmon, also known by rainbow trout and its scientific name Oncorhinchus mykiss, is a pacific salmon species found in the family Salmonidae. It is found in the Pacific basin, more precisely, from the latitude of northern Mexico to Alaska, as well as southwards on the Asian shore.

  • Life cycle of the species

Just like the Atlantic salmon, the life cycle of a Steelhead salmon depends on two different aquatic environments, mature fish spend most of their lives at sea to return every twelve months in freshwater to spawn, making them anadromous.

i. Fertilization
Fertilization occur between autumn and spring, with for first step, the creation of a series of nests called ‘redds’ (in riffles) by the female. Using body movement allow her to dig a depression in the fine gravel which varies between 50 and 150 cm2 and can receive a stream velocity of around 0.5 m/s. When the redd is ready to host the eggs, the female will lay her eggs (2000 eggs/kg body weigh) that are fertilized by the release of milt from the mature male into the water column. Finally, to protect the ova, the female will bury them to a depth than can reach 40cm.

ii. Hatching
Hatching occurs around 300-480 degree-days after fertilization (cooler the water temperature is, longer hatching will occur) and alevin will remain in the redd using their yolk reserve as resources. The main energy spent by the alevin is focused on the maximization of growth and a few is spent to maintain their position in the redd (negative phototaxis). The Hatching success rate range from 4% to 80% and depends on the water quality, temperature, and gravel. At higher temperature (15°C) it has been reported high egg mortality rate.

iii. Fry stage
At around 700 degree-days, the fry begins to expose themselves to the environment leaving the protection of the redd. They are carnivorous and territorial and must find food such as tiny insect as their yolk resource is almost gone (buttoned up). Fry will fill their swim bladder with air to float through water.

iv. Parr stage
Through the growth of the fry into a parr, lateral marking start to appear (like fingerprint), making it easier to identify and acting as camouflage during the parr stage. The duration of this stage varies between 1 to 3 years before undergoing significant changes. An Atlantic salmon and steelhead salmon parr are very lookalike and difficult to differentiate, the best clue you can get is the habitat as Atlantic salmon tend to prefer faster riffles.

v. Smolt stage
Oncorhinchus mykiss species can be a little confusing as it contains different strains, such as the Rainbow trou, for which, their entire life cycle is spent in freshwater, and the steelhead salmon, an anadromous fish that undertake extensive migration. However, this ability is likely due to an opportunistic behaviour (based on genetic predisposition). Therefore, The par-smolt transformation, also known as smoltification is faster than the Atlantic salmon. This metamorphose include a change in body shape, loosing lateral mark and a change of color.

vi. Kelt
In the wild, Survival rate after spawning is low. Usually, a mature female will spawn around 1-2 times but go up to 3 times, if they can make it that long, and after the first spawning she is known as a ‘kelt’. On the contrary, mature male will not live to spawn more than once. Adult Steellhead commonly reach 8-9kg but can also reach pretty big size, up to 14 kg or more.

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