Fin condition of fish kept in aquacultural systems

Abstract

Fish fi ns seem to be a suitable indicator of welfare state. In natural conditions there is no worsenig of fi n condition. Damaged fi ns occur in aquacultural systems only. They are characterized by shortening size, frayed rays, disturbing of fi n tissue, lesions and necrosis creation. Possible causes are aggressive behaviour of fi sh, inapropriately chosen size of stocking density, feeding management, diet composition, rearing system, water quality, thoughtless manipulation with fi sh and bacterial infections. Mostly, dorsal and pectoral fi ns are damaged in salmonids (not in percids). For evaluation there are all fi ns except adipose fi n used. Lenght of fi ns is measured and the visual aspect is assessed. Mostly used method is "Relative fi n length". Adjustment of rearing conditions, feeding ratio increasing, propriate diet composition (amino acids and minerals), rearing fi sh in duoculture, preventive baths in chloramine-T, prefering of ground canals and fi shponds can conduce to improving of fi n condition. Bad fi sh condition worsens swimming and it can rule the saleability of fi sh. Aquacultural systems do not allow natural fi sh farming. That is why it is necessary to assess welfare of kept fi sh. The fi n appearance informs about condition of rearing environment.