ABSTRACT: Studies on lymphoid organ spheroid (LOS) cells of Penaeus monodon were undertaken. Phenoloxidase and peroxidase assays showed that LOS cells have characteristics similar to semi-granular and, in particular, large granular haemocytes. The mean percentage of LOS cells positive for phenoloxidase and peroxidase was 85 ± 23 and 82 ± 23%, respectively. There was no significant difference between the sites of phenoloxidase and peroxidase activity in LOS cells (t = 1.617, df = 29, p > 0.05). The relative sectional area occupied by LOS cells relative to that of the stromal matrix cells from both laboratory-held and farmed prawns was not correlated to increasing weight or total length of the prawns (p > 0.05). An apoptosis detection assay showed that LOS cells were often apoptotic whilst stromal matrix cells were not. There was a significant difference (t = -5.533, df = 58, p < 0.05) in the mean percentage of apoptotic spheroid cells between laboratory-held prawns (52 ± 24%) and farmed prawns with midcrop mortality syndrome (MCMS) (80 ± 12%). In conclusion, LOS cells have the characteristics of exocytosed, granular haemocytes that have phagocytosed foreign material, particularly viruses, and probably constitute a major mechanism for penaeid antiviral defense.

KEY WORDS: Penaeus monodon · Haemocyte · Lymphoid organ · Spheroid cells · Prophenoloxidase · Peroxidase · Apoptosis · Midcrop mortality syndrome

Published in DAO Vol. 40, No. 2 (2000) on March 14
ISSN: 0177-5103. Copyright © Inter-Research, Oldendorf/Luhe, 2000