The mentioned cell in above blood cell smear of Nile tilapia should be Monocytes.
Also, other cells are nucleated Erythrocytes(RBC).
Monocytes are large leukocytes with an abundant blue-gray cytoplasm that lacks granules and are occasionally vacuolated.
As in mammals, monocytes migrate to the tissues and became macrophages. Aggregates of melanin containing macrophages normally occur within the liver, spleen, and kidney of fish and are also found in the liver of reptiles and amphibians.
In fish, Melanomacrophage centers (MMC) have been shown to trap and retain antigens and immune complexes, thus functioning as a primitive analog to the lymphoid germinal center. ( I attached reference article for you)
Thanks for the answer. Do you think they may be young monocytes?
Monocytes (normal, mature) are the largest leukocytes of fish (sometimes twice the size of the erythrocyte). These cells in the images are almost half of the erythrocyte.
In this smear, there are very typical monocytes. I think these cells in the picture may be young cells.
Soon, I will try to send images of the monocytes (very typical) of this same smear.
We have two books in Brazil about. The first is Hematologia de Peixes Teleósteos, the autor are Tavares-Dias and Moraes, 2004. The other is Metodos para análise hematológica em peixes, the autors are Ranzani-Paiva, Padua and Tavares-Dias.