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ß-Glucane in cultured flatfish in moderate latitudes

This binational research project between IMARE GmbH and East Sea Fisheries and Research Institute – ESFRI and National Fisheries and Research Institute – NFRDI, both South Korea, concentrates on the comparative culture of juvenile Olive Flounder (Paralichthys olivaceus) and Starry Flounder (Platichthys stellatus) in land based culture systems applying ß-1-3-Glucane enriched pellets.
β-Glucane is a polysaccharid gained from yeast cell walls. The immune- stimulating effect of Glucanes has been shown for different fish species. 

The Olive Flounder (Paralichthys olivaceus) is the most important commonly cultured fish in South Korea. The production in 2006 reached 48,852 tons and 48% of the whole finfish production in South Korea. The cultivation of Starry Flounder in intensive aquaculture is not very abundant at the moment. But Starry Flounder is an interesting candidate for aquaculture due to its market value and its high adaptive abilities to varying water conditions like salinity and temperature. In its natural habitat the Starry Flounder stays a part of its life in estuaries and far up into northern latitudes. That makes this species interesting especially for Recirculating Aquaculture Systems (RAS) in temperate zones; the reduction of salinity and reduced heating in winter can minimize costs.

For this project the effect of β-Glucane on the Olive Flounder will be monitored again and the effect will be tested for the Starry Flounder for the first time. Advantages and Disadvantages of the Starry Flounder compared to the Olive Flounder as a major aquaculture species will be monitored.
For this purpose juveniles of both species were chosen to analyze the effect of ß-1-3-Glucane enriched feed on immune system and growth of the fish. All individuals were bought at a commercial hatchery in Gangneung (South Korea). Respectively, half of the fish of each species was fed with β-Glucane enhanced food. The other half was fed with control food twice a day. The amount of consumed food and water quality parameters (T, S, O2, pH) were noted daily. The experiment was carried out for 10 weeks. During the first two weeks of the experiment the feeding behavior of the fish was observed. Every week 5 fish were randomly sampled, anesthetized, measured, weighed and samples of blood, mucus, digestive tract, and liver were taken. The concentrations of total cholesterol, Glutamat-Oxalacetat-Transaminase (GOT), Glucose, Albumin, and total protein in blood serum were measured. Serum lysozyme concentration was quantified. RNA/DNA ratio was measured with spectral scanning multimode reader. Digestive enzymes Amylase, Lipase Trypsin-like Protease for stomach and intestine were analyzed.

First results show a positive trend for the up growth of the fish fed with β-Glucane compared to the control fish. The feeding behaviour also shows interesting differences between the two species.
Further analysis of the data will show how the results can be used in future aquaculture projects and which aspects need further investigation. For now we can say that β-Glucane is a suitable feed additive for juvenile food. Both fish species show high potential for the use in RAS in Germany. 


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