There have already been other animals in space, but the idea of a dolphin floating with humans in a water-filled spacesuit is an amazing concept.
It looks like the title is (surprise!) "Dolphins in Space" by Richard J. Bartrop.
If we are to become a spacefaring species, we will have to create ways to bring other life (plant, animal, & fungal) along for the journey. Humanity cannot exist in a vacuum, both literally & figuratively.
I just noticed that the dolphin's suit has mechanical arms, which it's using to grasp the cable/tether. Perhaps we will find similarly outlandish solutions to enable other creatures to help us in various ways, instead of just being along for the ride. Then we can have a truly cooperative interspecies exploration of our Universe.