Salinity tolerance of cross-breed shrimp families: morphological and biochemical approaches

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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.