Substantial expansion planned

A fine specimen of brook trout Salvelinus fontinalis. Brook trout eggs account for a tenth of the production.

The Polish production of eyed eggs for rainbow trout is set to increase as concerns about biosecurity persuade farmers to establish their own hatcheries.

Rainbow trout is the most widely produced farmed fish in Poland after common carp. The fish is typically grown to a portion size of around 300-400 g, but some farmers also grow it to larger sizes over 1 kg. On-growing the fish in open raceways and, increasingly, in recirculation systems is well established in Poland. Successfully producing these fish calls for the use of high quality disease free eggs and the use of strains that grow rapidly, are disease resistant, and have other desirable traits, such as high stress tolerance. These eggs are often imported from other parts of Europe or the United States, but more and more eggs are being produced and supplied by local companies, either independent hatcheries or by trout farmers looking to backward integrate their operations.

Production set to increase significantly by 2018

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The Dabie Hatchery near Bytow produces top quality eyed eggs of rainbow trout (Oncorhynchus mykiss), brook trout (Salvelinus fontinalis), brown trout (Salmo trutta m. fario), sea trout (Salmo trutta m. trutta) and their hybrids, though rainbow trout eggs make up around 90% of the production. The hatchery was established by Krzysztof Grecki and Jacek Juchniewicz in 2003 with the first production of eggs in 2004. Today annual production has reached 140m eggs of which half is sold on the domestic market, while the other half is exported. The hatchery is growing, adding insulated new buildings that house circular tanks for the broodstock. The new construction will be completed shortly and within two years production will have increased to 200m eggs. Managing a hatchery is a technically demanding job that has to balance the demands of the market with the biology of the fish. For instance, rainbow trout normally spawn from September to May. Customers, however, can ask for eggs around the year. To accommodate this hatcheries maintain broodstock lines that have been selected or/and conditioned using exposure to light to spawn at different times of the year. However, the eggs that are placed on the market are normally only from fish between the ages of four and seven years of age in the case of rainbow trout and from 2.5 years in the case of brook trout. Since they spawn once a year the broodstock are thus typically only used three times.

In nature says Marcin Jesiolowski, the hatchery manager, the mortality of the spawning females is very high, 70-80% of them die after first spawning. In the hatchery, on the other hand, mortality rates are much lower at 20-25% per year, but we have to be prepared to constantly replace the fish that perish or for every 1,000 fish that we start with after seven years we will only have 130 fish left. Therefore, with each batch of eggs a certain number will go to another hatchery also owned by the owners of the Dabie Hatchery, where they will be hatched and grown as potential broodstock. These fish can then be transferred back to the Dabie Hatchery to ensure that it always has the broodstock needed for the production of eyed eggs. Once the fish have reached four years of age and are ready to spawn they are anaesthetised and the eggs massaged out. The fish are then released.

Genetic selection results in eggs with the best traits

A strong focus on genetics allows the Dabie hatchery to produce eggs that have low mortality, are uniform and result in fish with high disease resistance, growth rate, and carcass yield. The hatchery mainly delivers all female eggs to its customers. These are particularly useful for on-growing farms that are producing 300-400 g trout as the fish have not matured at this stage and have put all their effort into producing biomass. All female populations have other advantages too, the flesh tends to be better, they gain weight faster because of the lack of males that mature one year sooner and thus stop growing effectively, and they tend to be healthier. To other farmers that rear fish of 2-4 kg the hatchery can offer triploid eggs. These eggs result in sterile fish and as the fish does not expend any energy developing gametes this energy is instead directed at building biomass. As a result growth among triploids is faster compared with the usual diploid fish. Another advantage of sterile fish is that they cannot breed with wild stocks if they escape and thus have no genetic impact on the environment.

The hatchery is supplied with groundwater
from a source 200 m away that has a flow of some 20 l per second. As the facility uses a recirculation system, the use of new water is limited and this flow is adequate for the hatchery’s current requirements and will also be sufficient when the production is increased, according to Mr Jesiolowski. The existing recirculation system has also evolved over the past years. Originally the core of the system was a static biofilter, but this has now been replaced with a moving bed biofilter that uses Levapor media, a porous foam enriched with active carbon, that makes the biofilter significantly more efficient. The move to Levapor illustrates the continuous effort that goes into improving the efficiency of production by optimising the use of technology. The goal is ultimately to be able to serve the customers better, by offering them a superior product or even by being able to give them useful advice. The hatchery also has a consulting service providing advice to farmers who wish to establish their own hatcheries, a business that is increasing as farmers prefer not to bring fish in from outside for reasons of biosecurity. Another trend is to have facilities indoors rather than outside in order to insulate the production from natural fluctuations in temperature, the key parameter in growing the fish. The Dabie Hatchery illustrates well the evolution in the trout hatchery sector in Poland.