Do fish thrombocytes play an immunological role? Their cytoenzymatic profiles and function during an accidental piscine candidiasis in aquarium

Fish (F) thrombocytes (THRs) from healthy trouts were studied in terms of cytoenzyme expression. FTHRs were positive to acid periodic of shiff (PAS) and acid phosphatase (ac. phos.) without tartaric acid (-TA) stainings, as well to alkaline phosphatase. However, when compared with autologous macrophages (MOs), they were negative to naphthol cloroacetate esterase (AS-D), alpha-naphthyl acetate esterase (Anae), peroxidase (perox) and control ac. phos. with tartaric acid (+TA) stainings, thus indicating a lack of typical lysosomial enzymes. This evidence supports the notion that FTHRs are not true digesting cells. Quite interestingly, trouts and human MOs were positive for PAS, AS-D, Anae, and perox stainings, thus confirming that cellular cytochemistries are maintained across evolution as their phagocytic functions. Additionally, blood films from trouts, accidentally infected with Candida albicans in aquarium, were morphologically analyzed. Actually, FTHRs interact with erythrocytes, potentiating the formation of rosettes around a central MO. Polymorph nuclear cells and lymphocytes are present in these cellular aggregates, thus suggesting that FTHRs may represent a link between innate and adaptive immunity