Last time, we proposed a quizz, with five possible answers. Which one did you pick up ? Well, it almost does not matter since all possibilities but the D one have been observed in brown trout.
In this precise observation though, the individual is a male, and he's darting towards the egg to take a good meal. Eggs are indeed a good meal, full of energy, in a period of the year where food is scarce for many organisms.
This is the kind of interesting behaviour that you may discover, when you spend some time observing the reproduction in natural rivers. In my lab, we have been doing so for several years, using hand cam recorders or subaquatic cams too. Females use to digg a nest in the gravel for several hours, a time during which competition between males can escalate. At the precise time where female lay eggs, fertilization is very quick, often achieved by the closest male, but other males can participate too (multiple mating, as in the picture below).