White blood cells number is correlated to parasitic charge in the small spotted catshark Scyliorhinus canicula.

Hematology is now a useful diagnostic tool in human and domestic mammalian medicine and is becoming such also in the clinical evaluation of fish. Most of the current knowledge of fish hematology derives from research carried out on agnate organisms like missine and lampreys, on a few species of elasmobranchs and on some species of teleosts, although standardized hematological methods and reference intervals for elasmobranchs have not yet been established. The goal of this research was to compare the number of white blood cells present in the specimens of a population of lesser spotted dogfish (Scyliorhinus canicula) from central Mediterranean Sea with the parasitic charge. 75 sharks were collected in the Tyrrhenian Sea, 12 miles off of Rocchette Punta Ala, in Tuscany. Helminth communities were analyzed in the stomach, spiral valve, liver, gills, mouth and nostrils of all the sharks collected, while hematological analysis has been performed taking blood samples from venous sinus of the cardiac cavity of 32 sharks. Complete blood analysis has been performed for 10 samples, while for the remaining 22 only the leukocyte count was carried out using the fluorescence flow cytometry method. All the hematological parameters were correlated with each other, but just the correlation between the number of white blood cells and parasitic charge for the 32 sharks considered was extremely significant and inversely proportional, as the parasitized sharks showed fewer white blood cells than the not parasitized ones. The possible explanation of this result can be found in the immunosoppression from accumulation of trace elements (Hg, Pb, Cd, Cu, As, Zn) in the tissues of lesser spotted dogfish, as already demonstrated in some studies carried out on green frogs and bony fish.