Roundscale spearfish

What it is

This marine fish belongs to the billfish family. It has a robust body that is not heavily compressed. The upper side is dark blue, while the flanks show a coppery hue and the belly is silver. Iridescent bars may appear on the body. A moderate hump sits on the nape. The rostrum is long and slender, with a round cross section. Two dorsal fins are present, with the first being taller and rounded at the front. The scales on the sides are soft and rounded, which distinguishes it from similar species. The flesh is redder than that of related spearfish.

Where it lives

The species is endemic to the Atlantic Ocean. Specimens are frequently found near Madeira, Sicily, and the Straits of Gibraltar. They also inhabit waters off southern Portugal. Observations span the entire Atlantic basin from north to south. These fish are known to undertake long migrations across the ocean. They live in the epipelagic zone, spending most of their time at depths shallower than ten metres. The specific nursery areas for larvae and juveniles remain unknown to science.

How it lives

Little is known about their social behaviour. They are solitary migratory predators but may gather where prey is dense. They use their speed and rostrum to stun targets. Their diet likely includes schooling bony fish, squid, octopus and cuttlefish, similar to their relatives. They occupy a high trophic level. The fish possesses a swim bladder with small chambers for buoyancy. Parasites such as Capsala laevis may infect them. Research focuses more on individual movement than group dynamics due to the difficulty of studying these elusive animals.

Breeding and life cycle

Reproductive details are scarce. The species is dioecious, meaning individuals are either male or female. They likely lay eggs in batches in tropical waters. Only one juvenile and one egg have been recorded in scientific literature, both found in the Sargasso Sea south of Bermuda in April. The pelagic eggs contain oil droplets. They hatch into planktonic larvae that grow quickly into juveniles. Based on close relatives, the maximum lifespan is estimated to be between eight and fifteen years.

Fish and people

Commercial fisheries do not target this species directly. It is caught as bycatch in longline tuna and swordfish operations. For years, it was misidentified as white marlin, leading to inaccurate stock data. Studies suggest thirty per cent of recorded white marlin landings were actually roundscale spearfish. Recreational fishing generates significant revenue, with over ten thousand catches annually in the US alone. Although many are released alive, stress from capture causes an estimated twenty per cent post-release mortality. Gear changes like circle hooks may help reduce harm.

Status and threats

The species has no formal conservation status due to a lack of data. Historical landings for the combined white marlin group peaked in 1965 and have since declined. Current total allowed catches are often exceeded, risking stock recovery. Uncertainty in mortality rates and discard reporting complicates management. Assessing two species together may hide threats to one population. The situation appears precarious despite the absence of an official evaluation. Improved gear selectivity and strict release protocols are suggested to mitigate human impact.

Relatives and look-alikes

It was long confused with the white marlin, now classified as Kajikia albida. Genetic and morphological evidence in 2006 validated the roundscale spearfish as distinct. Key differences include scale shape and the distance between the anal opening and fin. It shares the genus Tetrapturus with three other species. Its flesh colour is more similar to the white marlin than to Tetrapturus belone.

Questions people ask about Roundscale spearfish

Good reading and sources

• Roundscale spearfish on WikipediaEncyclopedia
• Wikidata recordOpen data