Turbot charged
Turbot attracts renewed interest as aquaculture candidate in Kaliningrad
TURBOT ( Scophthalmus ma mus) is considered a valuable nutritional species in Europe and is successfully cultivated by many European companies located primarily in Spain and Portugal. Over the past ten years, China has become a world leader in turbot aquaculture, with a volume of about 55,000 tonnes per year, according to the FAO.
On the other hand, cultivation of turbot is not yet widespread, although there is a certain potential for this in other countries, such as Russia.
In this respect, the Kaliningrad region can be considered a promising area for turbot aquaculture in this country.
Today, the region is a Russian semi-exclave located on the coast of the Baltic Sea and sharing borders with Lithuania and Poland. The fish farming industry is so far only represented by freshwater species produced by small-holder farmer enterprises; these include common carp, rainbow trout, sterlet and African catfish. There are as yet no marine aquaculture species present.
It should be pointed out that farming of Atlantic (North Sea) turbot was introduced in the UK in the 1970s and, moreover, initial attempts at cultivation of Black Sea turbot ( Scophthalmus maeoticus), a species closely related to Scophthalmus ma mus were even conducted during the Soviet era.
Until recently, however, there was only little interest in the region in aquaculture with turbot from the Baltic Sea.
The Baltic Sea has very low salinity, ranging from almost freshwater level (3-8 ppt in the surface water) to 10 ppt in the deep basins. Adaptation to such environmental conditions has resulted in the turbot eggs in the sea developing in a demersal way, while all other populations of this species have pelagic eggs (Kuhlmann et al., 1980; Bagge, 1981; Florin, Höglund, 2006; Nissling et al., 2006; Martinsson, Nissling, 2011).
The effectiveness of natural turbot spawning at salinity levels below 6 ppt is low, and only a small number of newly hatched larvae survive (Kuhlmann, Quantz, 1980, Nissling et al., 2006).
This is consistent with the data on turbot distribution in the Baltic Sea. Thus, the abundance of species is higher in the southern part of the sea and by the island of Gotland, where the salinity level is about 7-8 ppt, compared with that in the Northern Baltic area, where it is about 5-6.5 ppt.
The species is completely absent in the waters of the Gulf of Bothnia, where the salinity level is 3 ppt (Nissling et al., 2006). In this case, the success of the natural reproduction of turbot is partly dependent on local upwelling events and salty currents from the North Sea, which lead to a short-term increase in the salinity level of the water surface layer.
Since the middle of the 1990s, turbot catches have been steadily decreasing in commercial fisheries over the whole Baltic Sea, where average total landings have been between 800 and 1,200 tonnes.
In 2018, the total catch did not exceed 370 tonnes, while the Russian catch was only seven tonnes (ICES, 2019).
In Russian waters, turbot are usually caught from April-May and September-November using bottom-set gillnets with a mesh size of between 110 and 240 mm, operated from small fishing vessels. This species usually comprises about 0.1-0.4 per cent of the overall fish catch.
Based on the above and taking into account a future increase in fish consumption, as well as the impact of an unstable hydrological regime in the Baltic Sea, not only commercial farming but also the implementation of artificial reproduction for stock enhancement programmes may be promising.
In modern Russia, the focus on turbot cultivation began in the mid-1990s in the facilities of the Atlantic Research Institute of Fisheries and Oceanography (now the Atlantic branch of the Russian Federal Research Institute of Fisheries and Oceanography or AtlantNIRO) in Kaliningrad.
Initial experiments focused on the incubation process and early larval stages of cultivation, but unfortunately the results did not show much promise; the survival rate of the turbot larvae was under one per cent.
Now, in conjunction with the implementation of the Strategy for the Development of the Fisheries Complex until 2030, developed by the Ministry of Agriculture of Russia (Russian Government, 2019), more investment will be made, not only in expanding existing aquatic bioresource production, but also in introducing the cultivation of new fish species. Thus, the turbot has recently attracted interest again as a candidate for aquaculture in the Kaliningrad region, because it is a species that is highly valued by local consumers as a healthy source of nutrition; it has a low body lipid content of about two per cent of fish meat and a highly digestible protein level of 16 per cent.
On the local market, wild turbot are usually sold frozen as gutted whole fish, fillets with skin or skinned fillets.
It is against this background that, over the past three years, from 2018 to 2020, the branch’s aquaculture department was tasked to develop proper cultivation protocols for turbot juveniles and adapt them to the region’s conditions.
Consequently, the main aims of this project were to investigate the feasibility and features of the cultivation of Baltic turbot juveniles.
Efforts have also focused on providing robust documentation concerning the methods of the most crucial technical procedures, such as the catch and transportation of wild turbot, broodstock management, artificial insemination and gamete management, egg incubation and further larval culture until 1g. The latter is considered one of the most difficult stages of turbot cultivation: it is the period lasting from the beginning of exogenous feeding until the complete metamorphosis of the larval body (turbot larvae are symmetrical after hatching), where mortality rates may be as high as 98 per cent. But after
Not only commercial farming but also stock promising” enhancement programmes may be
European white fish ( or onus la ar us .) as well as studies of its artificial reproduction. For the turbot trial, parts of the premises and RAS modules were redesigned and modernised.
Eggs and larvae were obtained from wild turbot breeders. The broodstock was captured in the Baltic Sea along the coast of the Curonian Spit in early June.
After transportation, the individual adults were put in experimental RAS, while males and females were kept separate, and early sexual maturation through temperature stimulation was conducted.
Artificial fertilisation was carried out using the semidry method, in which female eggs were collected by stripping and then put to soak in glass beakers, while male testes samples were homogenised and the resulting suspension with sperm introduced to the eggs through a gauze.
The fertilised eggs were incubated in 20 litre hatching jars using a water flow system with an increased salinity of 15ppt.
It was found that within the egg, a large proportion of abnormalities occurred in the embryo development of Baltic turbot under natural Baltic Sea salinity conditions. And since this local species has demersal eggs, the natural salinity of the sea water was adjusted with synthetic salt, to create a negative buoyancy. The average water temperature was maintained at 13.5oC and the incubation process lasted for 137 hours.
Newly hatched larvae were placed into tanks with microalgae cultures ( annochloropsis ocula a and unali lla salina) using the ‘green water’ technique.
The enriched rotifers ( Brachionus plicatilis) were introduced in a two-day post hatch (DPH) and maintained until 15 DPH, when r ia salina nauplii were offered at 8 DPH until 20 DPH.
Artemia metanauplii hatched from cysts were enriched with fat-soluble vitamins before being fed
Large scale farming will require reliable marketing and economic research”
to the larvae, and then offered in the period from 20 to 35 DPH. Starting from 30 DPH, in parallel with live feed, turbot larvae were fed an artificial diet until the end of the experiment.
From the first days after incubation, the water temperature was increased gradually from 13.5oC to 17.0oC by 0.5oC every day; it was maintained at this level until 15 DPH and then increased to 22.0oC on the final day of the experiment.
Over the course of the rearing process, a number of different shaped tanks were employed. In the early stages of larviculture, cylindroconical tanks were used. Then, from 20 DPH to 40 DPH, the turbot larvae grew in round, flat-bottomed fiberglass tanks with a water level of 20cm. From 40 DPH, the fish were placed into rectangular raceways. The light regime was 16 hours of light alternating with eight hours of darkness.
This research found that, by comparison with Atlantic turbot as well as Black Sea turbot, the highest mortality peaks were observed in the first three weeks of growth at 7-10 DPH, when the larvae fully opened their mouths and consumed rotifers in the water column. It was also at 18 DPH, during the transition from rotifers to artemia nauplii.
In the past year, over a period of 70 days post hatch, AtlantNIRO specialists managed to achieve a larval survival rate of ten per cent on rotifers, artemia and artificial diet feeding, which is considered a good result for this species, but still requires improvement.
A higher survival rate can be attained with copepods as the initial feed along with advanced hygiene and bacterial load control.
All the data obtained and results found over three years will be processed by the institute branch’s aquaculture department and will subsequently form the basis of a handbook on techniques of artificial cultivation of turbot, which local fish farmers can adopt and use themselves within the region.
So far, taking into account the existing worldwide turbot farming techniques and recent successful Russian attempts at cultivating this species, it is fair to conclude that the potential of turbot aquaculture in the Kaliningrad region looks very promising.
Looking ahead, the issues of possible restocking programmes and large scale farming will require reliable marketing and economic research.
Dmitry Pyanov is lead engineer at AtlantNIRO.