If you are looking to take photos of aquatic animals, a small glass aquarium gives the best results. However you run the risk of breaking it, particularly if you're hiking with it. Plastic always suffers from scratches so you can use it but you have to accept that the photos might not be as nice as behind glass. I've been using narrow rubbermaid containers for observation and transportation of aquatic animals (filled about 1/3 of the way). For photos I have been using a small glass aquarium (in the car) and a "critter corral" or some such from walmart when I can't carry glass.
Addition: I should add that I'm new to this so I'm not an expert on field work. I will however claim some skill and knowledge of how to get good photos so the glass versus plastic comment stands.