Adaptations of Crocodylus acutus and Alligator for life in saline water

• 1.1. American crocodiles (C. acutus) weighing less than 200 g are unable to grow when kept in 35 ppt sea water in the laboratory. Yet paradoxically there are some highly saline areas in south Florida where rapid growth occurs. It is possible that these conflicting observations can be reconciled by behavioral osmoregulation of young crocodiles.
• 2.2. Hatching occurs during the rainy season and small crocodiles may drink from the brackish “lens” available during and after rainfall.
• 3.3. Using a weekly regime of alternating exposure to 35 ppt (6 days) and 4 ppt (12–24 hr), it has been demonstrated that growth of small crocodiles occurs. Feeding takes place primarily when brackish water is available. Salinities as high as 18 ppt were drunk when crocodiles were dehydrated by 15–20% of initial mass.
• 4.4. C. acutus and Alligator have a rather low rate of water efflux in sea water (0.2ml/100g-hr).
• 5.5. Sodium influx in sea water of C. acutus is low, but higher than efflux. Thus there is no evidence yet for a significant role of the lingual salt glands in sodium excretion.
• 6.6. The major adaptations to saline water of hatchling C. acutus are a low intake of sodium, an ability to selectively drink water of lower salinities, and to grow very rapidly (within 3–4 months) to a size much more tolerant of immersion in 35 ppt sea water.