Fish Facts » Blackfin Tuna
As one of the smaller tuna species, the blackfin tuna has a robust, fusiform body, with small, compact scales completely covering the body. The mouth is oblique and the maxillary jaw terminates prior to the vertical from the center of the large eye. The corselet, a band of larger scales forming a circle around the body behind the head, is small and inconspicuous. Pectoral fins are moderately long, reaching below the origin of the second dorsal fin. There are separate finlets located behind the anal and dorsal fins. The lunate caudal fin has short keels at its base. Blackfin tuna swim primarily through movements of the caudal fin and body. The second spine on the dorsal fin is the highest with the first spine almost as high. The anal fin is similar in appearance to the soft, low dorsal fin. Anteriorly, the lateral line has a distinctive dip, descending posteriorly to the pectoral fin origin, then ascending to a point below the 3rd or 4th dorsal spine, then continuing straight to the caudal keel. The blackfin tuna has a bluish-black back with gray to silver sides and a white belly. A broad, brown stripe is located along the upper portion of the eye. There is a prominent yellow to golden-colored lateral band present on the sides, usually fading upon death. Small iridescent areas located on the sides of the abdomen are silvery. This area is sometimes marked with vertical rows of pale dots along with slightly elongate spots between these rows. The dorsal finlets are dusky with bronzy reflections and white edges while the ventral finlets are usually gray. The absense of yellow on these finlets distiguishes the blackfin tuna from all other tunas. However, the dorsal finlets sometimes fade to yellow upon death.
Occurring in oceanic waters in close proximity to the coastline, the blackfin tuna prefers clean water and warm temperatures, usually seaward from the continental shelf. It is a strongly schooling, migratory fish, often forming large mixed schools with skipjack tuna (Katsuwonus pelamis). During the summer months, the blackfin tuna migrates to temperate waters remaining above 70°F (21°C). It is most abundant off the Florida coast during autumn, winter, and spring.
Various fish, squid, amphipods, shrimp, crabs, and stomatopods constitute the diet of the blackfin tuna. It often feeds in surface waters where they form large mixed schools with skipjack tuna (Euthynnus pelamis). It directly competes with the skipjack tuna for prey, and is occasionally even preyed upon by it. Blackfin tuna feed by straining prey from the water as well as chasing and capturing prey which is then engulfed.
There is a major fishery off the coast of Cuba and throughout the Caribbean where it is common. Around south Florida and the Bahamas, the sport fishery is also important due to the proximity to deep water. This tuna is highly regarded for its fighting ability. The flesh is of excellent food quality and is marketed fresh, dried and salted, canned, and frozen. Off Cuba it is caught with poles and live bait, while elsewhere it is caught by trolling and drift fishing.
Blackfin tuna reach a maximum size of 39 inches (100 cm) in length and 46 pounds (21 kg) in weight. They are most frequently taken at an average size of approximately 19.75 inches (50 cm), corresponding to a weight of about 7 pounds (3.2 kg). Maturity is reached at lengths of 16-20 inches (40-50 cm).
The blackfin tuna is one of the few tuna with a limited range. It occurs only in the western Atlantic Ocean from Massachusetts (US) south to Rio de Janeiro (Brazil), including the Gulf of Mexico and Caribbean Sea. It is abundant in tropical regions, however in the northern Gulf of Mexico the yellowfin tuna (Thunnus albacares) is more common than the blackfin tuna. The blackfin tuna is a highly migratory species, moving into more temperate waters during the summer months.
Florida Museum of Natural History
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