Influence of Environmental Conditions in Ichthyophthiriasis Trigger to the Europeans Catfish Juveniles (Silurus Glanis) Stocked into a Production System with Partially Reused Water

Currently, in Romanian aquaculture, the rearing of the European catfish into intensive production systems raises a growing interest determined by its higher technological performances. In comparison with pond traditional aquaculture, the new farming systems are characterized by modified environmental conditions that may lead, in case of exceeding thresholds of tolerability, to occurrence of stress factors, thus setting the disease conditions. From this perspective, the purpose of this paper is to present the association circumstances of the predisposed environmental conditions that have weakened the fish body resistance promoting the pathological action of Ichthyophthirius multifiliis after the transfer of European catfish juveniles (G=33.6±1.7 g, L=17.5±2.9 cm) from a pond system into a tank culture system with partially reused water. During a 21-day period, some restrictive parameters of water quality have registered values far beyond the optimum interval for wells juveniles growth (t≤16oC, CmaxN-NH4+=3.62mg/l, CmaxNO2-=9.18mg/l, CmaxCl2=0.1mg/l) which caused the appearance of some characteristic symptoms, such as the gills brown coloration, masking the first symptoms of ichthyophthiriasis and contributing to the subclinical evolution of the disease. The concentrations of water chemical parameters were determined by spectrophotometer methods using Merck kits, analogous to standard methods. Subsequently, the “ich” diagnosis was confirmed by microscopic examination of the gills and skin scrapings highlighting the presence of parasites. In order to alleviate methaemoglobinaemia and parasite treatment, sodium chloride was gradually added in water till 1 ppt concentration. Maintaining the salinity of the system led to a reduction of gills parasitic intensity, while mature trophonts encapsulated in the skin were protected by mucus hypersecretion. Finally, the destruction of gill epithelium seriously affected the osmoregulation, resulting in fish death by asphyxia which led to a loss of 90% of the population