With lower light, your camera is going to struggle to capture your mandarins moving around. Your camera will try to compensate for the lower light by having a low shutter speed which affects the clarity of your video. Not sure what your skill level is at with a DSLR. Have you tried increasing the ISO to 800 possibly higher? This will make the video a little grainy but you're going to have more clarity. http://cinematography-howto.wonderhowto.com/how-to/film-using-dslr-low-light-0141568/ I feel like there might just not be enough light when your mandarins are spawning but give it a try.