What is "nurseryfish"

n. Any of the family Kurtidae of fish that carry their egg clusters on hooks protruding from the forehead of the males.

Kurtus is a genus of perciform fishes, called the nurseryfishes, forehead brooders, or incubator fish, native to fresh, brackish and coastal marine waters ranging from India, through southeast Asia to New Guinea and northern Australia. Kurtus is currently the only known genus in the family Kurtidae. They are famous for carrying their egg clusters on hooks protruding from the forehead ( supraoccipital) of the males, although this only has been documented in K. gulliveri and available evidence strongly suggests this is not done by K. indicus (where the hook likely also is too small to carry eggs). Females do not have a hook.

In addition to the egg hook, the kurtid gas bladder is enclosed in a tubular bony structure evolved from the ribs. In both species, the back is elevated into a hump shape.

Despite their unusual reproductive habits, little is known about these species. Historically they have proven very difficult to keep alive in aquaria, although recent success with K. gulliveri has been achieved by Tokyo Sea Life Park in Japan.