Here's a couple of pics of the Long-spine AKA Thread fin Cardinalfish.
From WetWebMedia:
"Apogon leptacanthus Bleeker 1856-57, Threadfin Cardinalfish. Indo-Pacific including the Red Sea. To a little over two inches in length. Found in dense school in the wild. This group in a friends aquarium."
And from MarineDepotLive:
"The Apogon leptacanthus grows up to 3 inches. The Longspine prefers a tank of at least 20 gallons with plenty of places to hide & swim. The Apogon leptacanthus is a carnivore and likes to eat variety of zooplankton, and meat based seafoods. The Longspine is a low maintenance fish and will be peaceful towards their tank mates. "
