processed routinely for histology, sectioned at 5 lm and stained
with haemotoxylin and eosin (H&E), Giemsa, and Chromotrope
2R modified trichrome (Weber et al., 1992). For TEM, small pieces
(2 mm3) of hepatopancreatic tissue from the same shrimp specimens
were fixed in 2.5% glutaraldehyde and 4% paraformaldehyde,
or 6% glutaraldehyde, in Millonig buffer followed by washing in
three changes of 0.1 M sodium cacodylate buffer and stained en
bloc in 0.5% aqueous uranyl acetate for 1 h. The fixed tissues were
embedded in epoxy resin 812 (Agar Scientific-pre-mix kit 812) following
dehydration through a graded acetone series. Thick sections
were stained with Toluidine Blue for viewing with a light microscope
to identify sections with suitable target areas. Ultra thin sections
(70–90 nm) of these samples were mounted on uncoated
copper grids and stained with uranyl acetate and Reynolds’ lead
citrate. Sections were examined using a JEOL 1210 transmission
electron microscope.