No red blood cells? No problem. Icefish, meet the Asian noodlefish https://news.northeastern.edu/2026/01/01/asian-noodlefish-red-blood-cells/

"Antarctic Icefish are famous for living without red blood cells, but they are not alone. A species of needle-shaped, warm-water fish also lacks #hemoglobin and red blood cells. Like #icefish, its veins are filled with translucent white blood... #noodlefish adults retain juvenile features... In many other #fish, juveniles don’t need to make red blood cells because they absorb oxygen through their skin"