Black tiger shrimps (Penaeus monodon) are able to survive and can be reared under various salinities, possibly by the cellular adaptation of their excretory system, particularly the antennal gland, which is known to regulate body fluid in crustaceans. We have investigated the morphological and biochemical alterations of the antennal glands in shrimp reared in 7, 15, or 30 ppt seawater. Drastic changes occur in animals reared under 7 ppt conditions. Ultrastructural studies of the antennal gland in shrimps reared in 7 ppt seawater have revealed that podocytic cells in the coelomosacs ramify with more cytoplasmic processes forming the filtration slits, and that the tubular labyrinth cells possess more mitochondria in their basal striation and a wider tubular lumen than those found in the other groups. Many apical cytoplasmic blebs from labyrinth cells have also been seen in the lumen of the labyrinths under 7 ppt conditions, a feature that is not as prominent under the other conditions. The expression and activity of the Na(+)/K(+)-ATPase in the antennal gland are also correlated with the surrounding environment: the lower the salinity, the higher the expression and activity of the enzyme. Immunohistochemistry results have demonstrated the highest staining intensity in the labyrinth cells of shrimps reared under 7 ppt conditions. Our findings thus suggest that one of the adaptation mechanisms of this shrimp to the surrounding salinity is the regulation of Na(+)/K(+)-ATPase expression in the antennal gland, in conjunction with subcellular changes in its excretory cells.

Marine invertebrates respond to fluctuations in their environment throughout development and growth. Homeostatic adaptation is mediated in part through the regulation of Na+‐K+ ATPase enzymes and members of this class of enzymes are localized to the antennal gland of many crustaceans. In this study, we investigated the morphological and biochemical changes of the antennal glands in eight families of cross‐breed post‐larval shrimp subjected to hypotonic (10 ppt) and isotonic (20 ppt) conditions. The greatest changes in the antennal glands were detected in the hypotonic condition with families two and five cross‐breed shrimp exhibiting the highest tolerance to this diluted salinity. The changes detected in hypotonic tolerant shrimp included enlargement of coelomosac and labyrinth spaces, the presence of many dense cytoplasmic globules in podocytes as well as highly wavy apical architecture of labyrinth cells. Several alterations were also observed at the subcellular level such as widening of the intercellular spaces between podocytes, organelle destruction, and decreased basal membrane in‐folding in labyrinth cells. In addition, shrimp exposed to hypotonic conditions displayed decreased expression of both α and β subunits of Na+‐K+ ATPase and decreased enzymatic activity. The changes observed in animals upon exposure to hypotonic stress are discussed.