The Roundscale Spearfish, is a species of marlin. It is believed to inhabit open waters. This species can reach a length of 184 centimetres (72 in) FL and the heaviest recorded fish weighed in at 21.5 kilograms (47 lb).
Though Roundscale Spearfish do often have the truncated dorsal and anal fins so can a white marlin. There are more predictable physical differences between the two species. The scales will look different. The individual scales of a white marlin are not very noticeable where those of the Roundscale Spearfish are much more distinct with a stippled look. The most sure way of telling them apart is to look at the anal fin and the anal vent. The front edge of the fin and the vent will be about 2 inches apart on a white marlin and about 5-6 inches (about the width of the anal fin) apart on a Roundscale Spearfish. So if you catch a white marlin that looks a little funny to you, look at the relationship of the fin and vent to see if you have caught a spearfish.
They are pelagic, off shore, deep water fishes. They feed at or near the surface, mainly on small and medium sized fishes and squids, including dolphin, sauries, flying fish, needlefish and pilot fish. They appear to be available all year in small numbers. Fishing methods are the same as for other billfish, but with lighter tackle. Most are taken incidentally.
This species is known from the entire tropical and subtropical Atlantic Ocean and Mediterranean Sea. Originally described from Madeira and reported from several other eastern Atlantic localities but only recently known with certainty from the western Atlantic.