Final answer:
Eating an octopus would likely provide you with the most water without the detrimental salt load, unlike consuming teleost fishes or seawater directly.
Step-by-step explanation:
Lost at sea, you would obtain (and subsequently retain) the most water from a meal of octopus. Consuming seawater is not recommended due to its high osmolarity, which is approximately three times higher than that of body fluids.
Drinking seawater leads to more thirst as the osmotic pressure drives water out of your cells to dilute the ingested salt. This contrasts with how our bodies handle hypotonic solutions, where excess water is excreted by the kidneys.
Marine organisms like sharks have evolved osmoregulatory mechanisms to effectively deal with the hypertonic marine environment by secreting excess salts through their gills and urine, and they also store large concentrations of urea to maintain isotonicity with the surrounding sea. Most marine invertebrates, including cephalopods such as octopuses, are osmoconformers that maintain body fluid concentrations similar to seawater. Therefore, eating octopus would likely provide you with the most water, without the detrimental salt load associated with consuming teleost fishes or seawater directly.