University of Zadar contributes to the development of Croatian mariculture

by Eurofish
Harvesting seabass

FARMED MARINE SPECIES INCREASE IN VALUE

Croatian aquaculture production is overwhelmingly dominated by marine species with output from freshwater farms playing a supporting role.

This article was featured in Eurofish Magazine 6 2024

The main marine-farmed species are European seabass, gilthead seabream, and bluefin tuna, followed by Mediterranean mussels and oysters. In addition, farmers produce small volumes of several other species including meagre, toothfish, rainbow trout, Atlantic salmon, goby, scallop, and sea sponge. In 2023, overall production was stable in relation to the year before. Reductions in volumes of tuna, seabass, and mussels were compensated by increases in seabream, oyster and other species. In value terms, however, the total climbed 14% thanks to increases in value of all the individual species and in particular of tuna which showed a 30% hike (Table 1). Seabass and seabream are grown to the larval stage in hatcheries, before being placed in nurseries, and then transferred as juveniles to floating grow-out cages in the sea. The entire process is carefully controlled from the broodstock to the harvest-ready fish. Cultivation takes place in almost all the coastal counties with the bulk of the production coming from Zadar county. Farmed white fish is sold mainly on the domestic market and exported to Italy. Production has grown over the years following growth in demand on the domestic and EU markets, improved technology, and investments in capacity. Another important species is tuna which is caught in the wild at 10-12 kg and carefully brought back to on-growing cages to be fattened to 30 kg and above. Almost the entire production is shipped to Japan, though recently markets have opened in the US, the EU, and other Asian countries.

Increase in value compensates for decline in volumes of freshwater farmed fish

Production of freshwater farmed species in 2023 slipped by more than 10% compared with 2022 to 3,700 tonnes. This was influenced by a 40% reduction in the production of white and grey mullets, the second most widely produced species after common carp. Production of common carp, the species that accounted for 62% of total freshwater aquaculture production in 2023 fell by over 7%. Grass carp and trout both recorded small increases and a group of other species including tench, bream, catfish, African catfish, Siberian sturgeon, grayling, saw almost a doubling in output from one year to the next, but from a low baseline figure of 55 tonnes. As with the marine farmed fish, freshwater aquaculture production too recorded a significant increase in value compared to the previous year. Carp sales by value increased 46% and all other species went up by between 10 and 28 percent. The only group to buck this trend was that of the “other” species whose value declined by 6% (Table 2). Carps are warmwater species and are bred in large earthen ponds that lie along river basins in the continental part of the country. They are farmed in polyculture with other carp species like grass carp, silver carp, and bighead carp as well as European catfish, pike-perch, pike, and tench. Producers supplement the natural feed in the ponds with cereals so that production is classified as semi-intensive. The coldwater salmonids are usually raised in concrete raceways in mountainous regions where the water is the right temperature and available in abundance. Rainbow trout is the most farmed species and production is often fully integrated starting with broodstock and culminating in market-sized fish. Production takes two years and the fish are fed with commercial feeds since the water is devoid of natural fodder and growth rates are critical to commercial success. Freshwater fish is sold mainly on the domestic market though in recent years a small part of the production has been exported to other EU countries. Farmed freshwater production, both warmwater and cold water has been declining over the years. The Croatian National Aquaculture Strategy to 2027 attributes this to disruptions in water supplies, predation, and the lack of systematic monitoring and prevention of diseases on fish farms.

A department for blue and green subjects

Started in 2011 the Department of Ecology, Agronomy, and Aquaculture is one of the newer of the 27 departments at the University of Zadar. It is split into “blue” and “green” parts, the former covering agronomy, while the latter offers an undergraduate programme in underwater science and technologies and a graduate programme in sustainable management of aquatic ecosystems. The undergraduate programme was developed with Plymouth University in the UK and is interdisciplinary with emphases on marine biology, archaeology, social science, and aquaculture – essentially everything related to the sea both above and below the surface, says Ivan Zupan, the deputy head of the department. That said, the programme also covers freshwater aquaculture, though to a lesser extent. Students can choose the direction in which they want to go, aquaculture, production, or management of aquatic resources, for example. The university is also part of Conexus, a network of coastal universities in the EU, which offer a joint master’s programme in marine biotechnology. Students spend semesters at universities in France and Spain, and in Zadar they can participate in an aquaculture and seafood processing track. Scholarships are available but the rules stipulate that only one or two from the same country can be granted aid which results in a very international group of students. Students from outside the EU are also eligible to apply and the possibility of winning a scholarship makes it particularly attractive for students from Asia and Africa; last year some 450 applications came in for 20 seats. The participating universities also benefit from the networks created by hosting foreign students.

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Not everything looks rosy for the aquaculture sector

Studying aquaculture may not be the best career option in the future, according to Lav Bavcevic, an associate professor at the department. He feels that the constraints on the raw material needed to produce fish feed as well as the increase in temperature brought on by climate change will inhibit the growth of the industry. The challenge will be to retain what has been created and not lose it. Growing fish deeper in the water column may be an option but it demands complex and expensive technological solutions which will push up the price of the fish beyond the reach of ordinary consumers and reduce the size of the market. The issue of climate change is one that severely affects the Mediterranean. The Atlantic so far is less threatened, but Dr Bavcevic thinks that population density along the coast and the pressure from competing users will prevent the development of aquaculture there. Offshore technology may be an option, but that too is expensive to develop, build, deploy, and run on a day-to-day basis. He cites FAO data that show that global production of carnivorous species has stagnated the last 15 years which he attributes to limitations in the supply of fishmeal, fish oil, and soy for fish feed production. He sees some prospects in alternate sources of fish raw material such as waste streams from the fish processing industry, as well as in greater efficiencies when using fishmeal and fish oil to produce feed, but these, he feels, will not make a material difference to the situation. Growing carnivorous fish on land will face the same constraints and is unlikely to improve the production figures, though from an environmental and technological perspective this development is interesting, he says.

Lav Bavcevic, an associate professor at the department, feels that industrial fish resources and climate change pose a severe threat to the aquaculture sector.

In Croatia, marine-farmed fish production has increased over the last decade to some 20,000 tonnes today and is likely to increase further. The company behind much of the growth has another site where the environmental impact assessment has been concluded and production can begin once they obtain a licence, says Dr Zupan. The site has a capacity of 5,000 tonnes and he expects production to go ahead despite the demanding logistics. Another company is looking at producing offshore in the open sea where they will test a new cage design to produce trout at a depth where the water is cold enough for the fish. This is already being attempted in the Velabit channel by another firm, says Dr Zupan, but there were mortalities because of the temperature. The company switched from trout to salmon and has now tested a submersible cage which reduced mortalities but is more complicated to service. In the Black Sea, Turkish companies are growing trout on land till the fish reach a 500 g or so and then introducing them into cages in the Black Sea for six months in the winter period where they grow to 3-4 kg. In theory, this could be done in the Mediterranean too, says Dr Bavcevic, but the challenge is finding a source of freshwater close to the coast for the initial growth phase. Other species are also being farmed in Croatia though production is still minor. These include species like meagre and common dentex. The latter is a new species and the price on the market is high because production is not yet very efficient, but this will change in the future as knowledge about the fish increases. Seabass and seabream have been on the market for 50 years and there is a large body of research devoted to these two species and the same can be expected of common dentex, Dr Bavcevic expects.

Increasing bivalve production is an important research topic

Bivalve production is also a subject of interest for the department where researchers are working to increase and improve the production. We are looking at some new species of bivalves, Dr Zupan says, and at how to improve the current technology. He has just concluded two projects supported with European money in which researchers worked on oyster feeding trials and with the Mediterranean scallop which is an interesting species from a market perspective. The department has one Ph.D. candidate working on the reproduction of these species, collecting them from the wild and trying to get them to reproduce several times a year rather than one or two times as in the wild. Several types of microalgae are needed for these trials as feed for the bivalves which researchers are trying to produce in a big industrial bioreactor, the only one of its kind in Croatia. Identifying the right algal feeds for the bivalves and the proper sediment are important parameters to encourage them to spawn which could ultimately be the foundation for establishing a  hatchery. Commercial bivalve production in Croatia depends entirely on the collection of spat from the wild rather than from growing it in hatcheries. The Adriatic like the rest of the Mediterranean is quite oligotrophic and the only nutrient-rich parts are those areas near the mouths of rivers. The main production areas are Novigrad and the Lim channel in Istria, at the Krka river near Zadar, and Mali Ston bay near Dubrovnik, where bivalves have been produced for centuries. But production is limited because these areas are often in nature reserves or parks, predation by seabream is a challenge, and there is competition with other industries like tourism.

The high meat quality of the Mediterranean scallop (Pecten jacobaeus) makes it an interesting species to try and farm particularly as the population in the wild is estimated to be declining.

Mussel rafts from Galician rías are tested in the Adriatic

The industry is also highly fragmented with an estimated 200 producers producing an average of 10-20 tonnes, with the odd farmer reaching 100 tonnes. The small volumes preclude the use of technology and most of the work is done manually. There is a lot of scope for greater efficiencies and higher productivity, and researchers at the department brought a mussel raft from Galicia to test it in the production zone near Zadar. The raft allows the farmer to exploit 15 to 20 m of the water column rather than two to three metres they use currently. This would allow them to expand production three or four times from the same area. The researchers also tested longlines as used in New Zealand, which again is a more intensive production, but that did not elicit interest among investors. The imported rafts were not the traditional wooden structures but made with reinforced concrete. They have a much longer life, but are also quite expensive. A new 24 m x 24 m raft made of concrete is about EUR120,000. Dr Zupan says some farmers from Istria showed an interest in the rafts in part because they could use nets to protect the mussels from seabream predation. The different trials that are ongoing with respect to bivalve farming should at some point result in an increase in the production of these molluscs.

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