Hi 'jandjandlemur'..... Wildebeest is already accepted for Gnu but the Gar is a sea fish and the Pike is freshwater and not related to the Gar. Likewise the Blackbird is from the thrush family whereas the Mynah is of the starling family and different birds altogether, although there are resemblances to be found in these animals.
Actually, the majority of fish in the Gar family are not sea-dwelling, according to Wikipedia. You may be thinking of the "garfish", a sea-dweller also known as a "garpike" despite not being closely related to gars or pikes. Just FYI. Anyway, fun quiz!
You should accept gar, but not pike. You're correct that gar and pikes are not at all closely related, but gar are freshwater animals; and the picture you have is definitely a gar, not a pike. They do look superficially similar, but the tail is a dead giveaway.