Haematological responses of the Indian major carp Labeo rohita to saprolegniasis

Abstract

Saprolegniasis (cotton wool disease), due to infestation by Saprolegnia parasitica, is a major fungal disease in fish. Present study was conducted in the Indian major carps, rohu, Labeo rohita (Hamilton, 1822). Fingerlings of rohu (10.5±2.2 g) were artificially infected with the fungal parasite S. parasitica via injection (T1), cohabitation (T2) as well as immersion (T3) and compared with a control group (T0) with no infection. Blood samples were collected at 15 days interval over a period of 45 days and analysed for haematological parameters. Haemoglobin level in infected fish was lower (p≤0.05) than non-infected fish on 15, 30 and 45 days post-infection (dpi) except in cohabited fish on 45 dpi. Total erythrocyte count (TEC) in infected fish was lower (p≤0.05) than non-infected fish on 15, 30 and 45 dpi. Total leucocyte count (TLC) was higher (p≤0.05) in infected fish on 15 dpi; however no difference (p≥0.05) was noticed on 30 dpi. TLC in injected group was higher (p≤0.05) than control group on 45 dpi. Haematocrit (Hct), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC) and leucocrit (Lct) values in infected group were lower (p≤0.05) than control group. There was no difference (p≥0.05) in mortality among the groups on 15 dpi; however, on 30 and 45 dpi, the group subjected to immersion exposure recorded highest mortality followed by injected and cohabitated groups. Varying degrees of histological alterations were observed in the tissues due to the fungal infestation. The results indicated that S. parasitica significantly altererd the blood profile of infected rohu leading to 45-50% mortality. Therefore appropriate management measures need to be adopted for preventing infestation by S. parasitica in carp culture systems for realising sustainable fish production.