It is indeed a fish, but they look and act a bit more like a lengthy frog or ribbon-like salamander. They're found in swampy areas in a number of Southeast Asian countries and, once you've seen one, they're pretty hard to mistake for anything else!
Here's one I spotted on the banks of the Mekong, just west of Ho Chi Minh.
![Mudskipper on the banks of the Mekong River in Vietnam, just west of Ho Chi Minh](https://static.wixstatic.com/media/a27d24_60c24fbb82eb482999f3b12e8e12825d~mv2.jpg/v1/fill/w_147,h_83,al_c,q_80,usm_0.66_1.00_0.01,blur_2,enc_auto/a27d24_60c24fbb82eb482999f3b12e8e12825d~mv2.jpg)