Seasonal occurrence of diseases in a recirculation system for salmonid fish in the Czech Republic

Abstract

Aquaculture represents the fastest growing animal husbandry in many countries. However, higher intensity of fish farming can pose higher health hazards, too. We monitored the health status of fish from one fish farm in South Bohemia and discovered the main health problems in the breeding. For two years we examined a total of 224 specimens of brook trout (Salvelinus fontinalis), 126 specimens of hybrids (S. fontinalis×S. alpinus), 49 specimens of rainbow trout (Oncorhynchus mykiss) – all clinically healthy, and 100 clinically diseased or freshly dead fish. We registered skin erosions mainly in the caudal peduncle and tail fin. Two parasite species were identified (one protistIchthyophthirius multifiliisand one nematodeRaphidascaris acus) by parasitological examination. The epidemiological indicators ofI. multifiliiswere low. The prevalence of adultR. acuswas 0–86% with a maximum in June. From November, capsules with larval stages ofR. acusappeared in internal organs. Their highest intensity (200 pieces) and prevalence (100%) were detected in October. By microbiological examination of skin and gills, we identified changes in the density of bacterial population and its species composition dependent on water temperature and fish density. The most important problem on the monitored fish farm seems to be furunculosis of salmonid fish in all clinical forms, and the high intensity of larval stages ofR. acus. The originality of this study is based on the fact that the observed breeding employs the first Danish recirculation system in the Czech Republic and no recent information about health problems has been available.