Ichthyological terms, not general ones.
Subdominant male individual of certain fish species that attempts to sneak into the nest of a spawning pair and fertilise deposited eggs. Typically smaller in size and/or possessing reduced colouration compared with a normal male. Also known as a sneaky male.
See sneaker male.
Behavioural strategy seen in certain nest-building fishes in which one or more males that are not an accepted part of a spawning event fertilise some eggs. Such individuals are commonly referred to as sneaker, sneaky or satellite males.