Fin condition of fish kept in aquacultural systems

Abstract

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

Keywords

• fin erosions
• welfare
• aggressive behaviour
• nutrition
• manipulation
• bacterial infection