This question: Can you get enough water by eating only fish? asks if a person could survive on fish alone. Can a person survive on fish and/ or blood alone of any species if stuck at sea or animal blood as a last resort where there is no water or fire? 

Obviously if it was a fresh water fish there is water, but there are fresh water mud skippers that can breathe air and the water to tainted to drink in that case a fresh water fish blood maybe safer than the water. https://chemistry.stackexchange.com/questions/115901/what-can-i-eat-that-will-help-metabolize-blood

Desalination would be the best way to process the blood but this is in emergency situation scenario.

From @PTwr Comment's Link: If you drink blood regularly, over a long period of time the buildup of iron in your system can cause iron overload. This syndrome, which sometimes affects people who have repeated blood transfusions, is one of the few conditions for which the correct treatment is bloodletting. https://what-if.xkcd.com/98/

Blood is not a good source of water.
1 liter of blood contains about 800 mL of water, 170 grams of protein and 2 grams of sodium (calculated from the composition of lamb blood).
When metabolized, 170 grams of protein yields the amount of urea that requires 1,360 mL of water to be excreted in urine (calculated from here); 2 grams of sodium requires about 140 mL of water to be excreted (from here).
This means that drinking 1 liter of blood, which contains 800 mL of water, will result in 1,500 mL of water loss through the kidneys, which will leave you with 700 mL of negative water balance.
Fish blood can contain less protein, for example, trout (check Table 1) contains about 120 g of protein (plasma protein + hemoglobin) per liter of blood. Using the same calculation as above (1 g protein results in the excretion of 8 mL of urine), drinking of 1 liter of trout blood, which contains about 880 mL of water, will result in 960 mL of urine, so in 80 mL of negative water balance.
Turtle blood can contain about 80 g of protein (plasma protein + hemoglobin) and 3.4 g of sodium per liter. Drinking 1 liter of turtle blood, which contains about 920 mL of water, will result in 80 x 8 mL = 640 mL loss of urine due to protein, and ~240 mL due to sodium, which is 880 mL of urine in total. This leaves you with 40 mL of positive water balance (to get 2 liters of water per day you would need to drink 50 liters of turtle blood, which isn't realistic.
In various stories (The Atlantic, The Diplomat, The Telegraph), according to which people have survived by drinking turtle blood, they have also drunk rainwater, so we can't conclude it was turtle blood that helped them. I'm not aware of any story that would provide a convincing evidence that the blood of turtle or any other animal is hydrating.
