Subject: Having the shape and size of a twig, the very cryptic Shortnose Pipefish (Micrognathus andersonii) is quite difficult to spot. With hundreds of different species a correct identification of these Seahorse relatives (the Syngnathidae family) is not always easy. Many books and identification guides only mention a handful of species.
Technique: Keeping small subjects in focus can be tricky. If they go a bit back or forward they tend to go out of focus very quickly. The easiest way to counter this is to change your aperture. A smaller aperture (high f-stop) will give a bigger depth of field and put more things in focus. Because a smaller aperture will also reduce the amount of light entering the camera it is necessary to increase the light intensity by for example repositioning your video lights. Later in post production you can always mask parts of your image by adding a gaussian blur so that the focus remains on your subject.