Values of haematological indices of wels (Silurus glanis L.) in relationship to the level of nutrition during the pre-spawning period

The goal of this paper was to evaluate the effect of different nutrition le vels on condition and health expressed by means of selected haematological indices of both males and females of wels (Silurus glanis L.) during the pr e-spawning period. For 2 months of the pre-spawning period, brood wels were separated into groups reared similarly but with different level of nutriti on. The ratio of fodder fish biomass : wels biomass in 1995 was 3.2:1 in ma le group A; 1.1:1 in male group B; 2.6:1 in female group C and 0.9:1 in fem ale group D; while in 1997 this ratio was kept 2.3:1, 0.7:1 and 0.2:1 in fe male groups A, B and C, respectively. Prior to the anticipated reproduction, haematological examination considere d red blood count indices (red blood count - RBC, haematocrit - PCV, haemog lobin - Hb, mean corpuscular volume - MCV, mean corpuscular haemoglobin - M CH, mean corpuscular haemoglobin concentration MCHC, erythrocyte sedimentat ion rate) and white blood count indices (leukocyte count - Leuko, leukogram me), along with concentration of total protein in blood plasma (TP). Altoge ther, 15 males and females were checked in 1995 while 18 females were check ed in 1997. Both males and females which had been reared during the 1995 and/or 1997 pr e-spawning period with higher level of nutrition reached expressively highe r relative weight gain and significantly higher total protein (TP) in blood plasma (P < 0.05; P < 0.01) compared to those with lower level of nutritio n. Moreover, significantly higher PCV, Hb and MCH (P < 0.05) were found in group of females with higher nutrition level in 1995, compared to those wit h a lower one. A significantly higher percentage of lymphocytes (P < 0.05), as well as a lower percentage of granulocytes and their developmental form s (P < 0.05) were found in a group of females with higher nutrition level i n 1997 compared to those with lower nutrition levels. No significant differ ences were found in other haematological indices among the respective group s of brood wels. Results gained report for a more favourable condition of b rood wels reared at higher nutrition level (ratio of fodder fish biomass : wels biomass 2.3:1 - 3.2:1) during the pre-spawning period and a higher non -specific disease resistance may be anticipated also. Relationships between nutrition level and values of production, haematological and reproductive characters of the fish under study were discussed.