Bullet tunaBLT

BLT
37.5 cm TL

Characteristic features:

  • Large median keel with 2 smaller keels on either side of caudal peduncle
  • Tongue with 2 longitudinal ridges
  • Dorsal fins widely separated
  • 10–12 dorsal-fin spines
  • 8 dorsal finlets, 7 anal finlets
  • Teeth small and conical in single series
  • Interpelvic process single, large
  • 43–48 gill rakers on first gill arch

Colour:

Bluish black to purple above, silver below. Scaleless corselet area containing ~15 vertical dark bars behind first dorsal fin.

Size:

Up to 50 cm TL (smaller than Auxis thazard) and up to 1.84 kg in weight.1

Distribution:

Circumglobal in warm waters.

View FAO distribution map

Habitat:

Inshore pelagic, found at depths from the surface to 200 m.

Biology:

Mostly eats small fishes, particularly clupeids, and also squid, crustaceans and zooplankton such as crab and stomatopod larvae. Highly migratory forming same and multi-species schools. Maturity varies by region, length at 50% maturity for both sexes is estimated to be 24 cm FL in India and 18.8 cm FL in the Philippines.23 Age of first maturity in Japan is 1.25 years.4 Auxis rochei is a multiple spawner producing between 31,000–162,800 eggs per spawning depending on the size of the fish. Eggs are pelagic and considered an important part of the food web due to their high abundance. Maximum age is estimated at 5 years.5

Indonesian fisheries:

No dedicated fishery for Auxis rochei exists. Auxis rochei are caught with other species using lift nets, purse seines, shore seines, pole-and-line and by trolling.

Similar species:

Auxis thazard
Frigate tuna
FRI
Auxis thazard differs in having a wider posterior end of corselet of 10–15 scales wide under origin of second dorsal fin (vs. 1–5 scales); bars on dorsal scaleless area oblique to nearly horizontal (vs. more vertical); dorsal scaleless area longer, extends anterior of pectoral-fin tip (vs. shorter, extending posterior of pectoral-fin tip) and 36–42 gill rakers on first gill arch (vs. 43–48).

 

Euthynnus affinis
Mackerel tuna
Euthynnus affinis
Euthynnus affinis differs in usually having ~3 black spots present between pectoral- and pelvic-fin bases (vs. none); a narrow inter-dorsal space (vs. wide) and 29–34 gill rakers on the first gill arch (vs. 43–48).

 

Katsuwonus pelamis
Skipjack tuna
Katsuwonus pelamis
Katsuwonus pelamis differs in having 4–6 dark, longitudinal stripes on belly (vs. none); a narrow inter-dorsal space (vs. wide); interpelvic process 2 flaps (vs. single, large) and 53–63 gill rakers on the first gill arch (vs. 43–48).

 

Sarda orientalis
Striped bonito
BIP
Sarda orientalis differs in having a tongue without ridges or teeth (vs. 2 longitudinal ridges); a narrow interdorsal space (vs. wide); 5–11 narrow dark stripes on upper sides (vs. ~15 vertical dark bars in scaleless corselet area) and 8–13 gill rakers on the first gill arch (vs. 43–48).

 

Thunnus spp.
True tunas
Thunnus albacares
Thunnus spp. differ in having an interpelvic process of 2 short flaps (vs. single, large); a body covered in small scales behind corselet (vs. a dorsal scaleless area) and a narrow interdorsal space (vs. wide).

References

1.
IGFA. IGFA world record game fishes. International Game Fish Association Dania Beach, Florida. 2011;
2.
Collette BB, Cole K. Reproduction and development in epipelagic fishes. Reproduction and sexuality in marine fishes: patterns and processes University of California Press, Berkeley. 2010;21–63.
3.
Muthiah C. Maturation and spawning of Euthynnus affinis, Auxis thazard and Auxis rochei in the Mangalore inshore area during 1979-82. CMFRI Bulletin. 1985;36:71–85.
4.
Niiya Y. Age, growth, maturation and life of bullet tuna Auxis rochei in the Pacific waters off Kochi prefecture [Japan]. Bulletin of the Japanese Society of Scientific Fisheries (Japan). 2001;
5.
Jasmine S, Rohit P, Abdussamad EM, Koya KP, Joshi KK, Kemparaju S, et al. Biology and fishery of the bullet tuna, Auxis rochei (Risso, 1810) in Indian waters. Indian Journal of Fisheries. 2013;60(2):13–20.