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The ploidy of silver crucian carp Carassius auratus gibelio individuals, originating from nine natural habitats of Hungary, was estimated by erythrocyte nucleus area analysis. On the basis of DNA polymorphism, the genetic homogeneity or heterogeneity and the chromosome number of different offspring derived from the crossing of triploid and diploid populations and of two types of silver crucian carp females with other cyprinid males (Cyprinus carpio, Carassius carassius, Carassius auratus and Barbus conchonius) were determined. The results of chromosome and RAPD analysis demonstrated that diploid females could reproduce sexually with silver crucian carp and other cyprinid males and that the offspring of intra-and interspecific crosses contained the paternal DNA. Triploid females usually reproduced by gynogenesis and their offspring were clones, however, in very rare cases paternal genes were actually transmitted (i.e. paternal leakage) to the offspring and the progeny were triploid interspecific hybrids. RAPD analysis showed that while the paternal DNA appeared in the offspring, the maternal phenotype was strongly expressed. # 2005 The Fisheries Society of the British Isles

In a long-term growth trial, transgenic tilapia Oreochromis niloticus L. showed a 2·5-fold increase in growth compared with non-transgenic siblings. At 7 months, mean mass of transgenic tilapia was 653 g compared with 260 g for non-transgenic siblings. A significant increase (P<0·01) in head : total length ratio, viscera-somatic index and hepato-somatic index was observed in transgenic fish. Female gonado-somatic index (I G ) was found to be lower in transgenics than non-transgenic siblings in both mixed and separate culture conditions. Transgenic male I G values were found to be higher in mixed culture and lower in separate culture than that of their non-transgenic siblings. Food conversion efficiency was more than 20% greater in the transgenic fish. In a second shorter-term growth performance trial, the transgenic fish grew to about four times the size of their non-transgenic siblings. A digestibility trial suggested that transgenic tilapia were more efficient utilizers of protein, dry matter and energy. Apparent digestibility of protein and apparent energy digestibility were higher in the transgenic fish. 2001 The Fisheries Society of the British Isles

At the beginning of early 1990s the Food and Agriculture Organisation (FAO), the Organisation for Economic Cooperation and Development (OECD) and the European Union (EU) Commission effectively focused on multifunctionality, while in Hungary this term has only been highlighted in the last few years. As a consequence of the changes in Hungary in the last 15 years pond fish farms have had to explore their potential to find out how they can diversify their activities in order to be able to produce various fish products and to provide services for which there is demand from the market and the society. The application of the multifunctional approach has proved to be a realistic option for many fish farms for their survival and sustainable development. This paper demonstrates some examples of multifunctional fish farms, which clearly shows the business opportunities lying in the diversification of farm activities.