Abstract:

Haematological parameters of tench (Tinca tinca) infected by Saprolegnia spp. were studied. All parameters, except mean corpuscular volume (MCV), decreased in response to infection. A significant (P < 0.05) decrease was observed in haemoglobin (Hb) (-26.85%), red blood cell count (RBCc) (-20.94%), leucocrit (Lct) (-24.14%), and mean corpuscular haemoglobin concentration (MCHC) (-9.06%). Haematocrit (Hct), white blood cell count (WBCc), and mean corpuscular haemoglobin (MCH) also decreased (-7.66%, -12.44%, and -6.19%, respectively); however, differences between the infected and control groups were not significant. Among the parameters, only MCV had a non-significant increase (+7.84%) in the infected fish. The study results show that saprolegniasis caused anaemia and immunosuppression, followed by mortality in tench. Mortality was attributed to haemodilution caused by haemorrhaging and the breakdown of osmotic balance due to tissue (skin and muscular layer) destruction via the penetration of the hyphae; however, lethargy was another mortality promoting factor. Mortality among the Saprolegnia-infected fish also depended upon the initial site of infection, type of tissue destroyed, growth rate of the fungus, and ability of individual fish to withstand the stress. The present study was conducted to investigate physiological impairment in Saprolegnia-infected Tinca tinca under laboratory conditions; however, further studies at the population level in natural habitats and under similar stress conditions are needed.

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