Osmoregulatory power influences tissue ionic composition after salinity acclimation in aquatic decapods

Area of Science:

• * Crustacean physiology
• * Comparative osmoregulation
• * Inorganic ion transport

Background:

• * Decapod crustaceans exhibit varied salinity tolerance (euryhalinity) and osmoregulatory capacities.
• * Cell volume regulation involves the exchange of inorganic ions between extracellular fluid and intracellular (tissue) compartments.
• * Understanding these ion exchange mechanisms is crucial for comprehending decapod adaptation to diverse aquatic environments.

Purpose of the Study:

• * To investigate the interplay of inorganic ions between hemolymph and muscle tissues in four decapod species.
• * To compare osmoregulatory responses across species with different habitat preferences and regulatory strategies.
• * To determine how salinity challenges influence hemolymph and muscle ion concentrations, muscle hydration, and ninhydrin-positive substances.

Main Methods:

• * Four decapod species (Litopenaeus vannamei, Callinectes danae, Macrobrachium acanthurus, Aegla schmitti) were subjected to salinity changes (reduced for marine/estuarine, increased for freshwater species).
• * Hemolymph and muscle samples were analyzed for osmolality, sodium, chloride, potassium, and magnesium concentrations.
• * Muscle hydration and ninhydrin-positive substances were quantified to assess cell volume regulation.

Main Results:

• * Species exhibited distinct responses: Litopenaeus vannamei showed minor hemolymph dilution and increased muscle hydration; Callinectes danae displayed hemolymph dilution and reduced muscle sodium chloride.
• * Macrobrachium acanthurus maintained stable muscle ions and hydration, indicating effective hypo-regulation; Aegla schmitti showed altered hemolymph chloride and increased muscle ions and ninhydrin-positive substances.
• * Significant ion exchange between hemolymph and muscle pools was most pronounced in Callinectes danae and Aegla schmitti, correlating strongly with their comparatively lower extracellular regulatory power.

Conclusions:

• * The interplay between extracellular and tissue ionic pools is a key factor in decapod osmoregulation, particularly in euryhaline species.
• * Species with less robust extracellular osmoregulatory mechanisms rely more heavily on intracellular ion adjustments for cell volume regulation.
• * These findings highlight the diverse strategies employed by decapods to maintain osmotic homeostasis across varying salinity conditions.