Skipjack tunaSKJ

Katsuwonus pelamis
32.7 cm TL

Characteristic features:

  • Large median keel with 2 smaller keels on either side of caudal peduncle
  • 53–63 gill rakers on the first gill arch
  • Interpelvic process with 2 flaps
  • Teeth small and conical in single series
  • Tongue with 2 longitudinal ridges
  • Narrow interdorsal space
  • Body scaleless behind a scaled corselet

Colour:

Purplish black above, sides and belly silvery with 4–6 distinct dark longitudinal stripes.

Size:

Up to 110 cm TL, and up to 34.5 kg in weight.1

Distribution:

Circumglobal in tropical and warm temperate waters.

View FAO distribution map

Habitat:

Inshore pelagic to oceanic. Found in waters warmer than 15°C and at depths from the surface to 260 m.

Biology:

Feeds on fish, crustacean and cephalopods, preyed upon by larger pelagic fish. Occurs in large numbers and forms large schools. Size at first maturity of females is estimated to be between 39.9–50 cm FL,2,3 with nearly all females considered mature at 59 cm FL.3 In the eastern Pacific Ocean all females aged 16 months or older are assumed to be mature.4 In the west Indian Ocean Katsuwonus pelamis spawn year round with 2 peaks of active spawning during the north and south monsoons.5 Periods of active spawning become shorter as distance from the equator increases. Fecundity increases with size of fish the number of eggs produced per season by a female of 41–87 cm FL ranges between 80,000–2,000,000. This is a productive species being fast growing, highly fecund and short lived, with an estimated maximum age between 6–8 years.6

Indonesian fisheries:

Caught mainly by purse seining and by pole-and-line.

Similar species:

Auxis spp.
Bullet & Frigate tuna
Auxis rochei
Auxis spp. differ in having a wide interdorsal space (vs. narrow); no stripes on the belly (vs. 4–6 dark, longitudinal stripes); a series of oblique dark stripes on dorsal scaleless area (vs. no markings) and 36–48 gill rakers on the first gill arch (vs. 53–63).
Euthynnus affinis
Mackerel tuna
Euthynnus affinis
Euthynnus affinis differs in having no stripes on the belly, but usually 3 spots between pectoral- and pelvic-fin bases (vs. 4–6 dark, longitudinal stripes on the belly); a series of oblique dark stripes on dorsal scaleless area (vs. no markings) and 43–48 gill rakers on the first gill arch (vs. 53–63).
Sarda orientalis
Striped bonito
BIP
Sarda orientalis differs in having 5–11 narrow dark stripes on upper sides (vs. 4–6 distinct dark longitudinal stripes on lower sides); tongue with 2 longitudinal ridges (vs. without ridges or teeth); body covered in minute scales behind a corselet of well-developed scales (vs. body scaleless behind a scaled corselet) and 8–13 gill rakers on the first gill arch (vs. 53–63).
Thunnus spp.
True tuna
Thunnus albacares
Thunnus spp. differ in having vertical bars/stripes and/or rows of spots on belly (vs. horizontal stripes).

References

1.
Collette BB, Nauen CE. FAO species catalogue. Volume 2. Scombrids of the world. An annotated and illustrated catalogue of tunas, mackerels, bonitos and related species known to date. 1983.
2.
Batts BS. Sexual Maturity, Fecundity, and Sex Ratios of the Skipjack Tuna, Katsuwonus pelamis (Linnaeus), in North Carolina Waters. Transactions of the American Fisheries Society. 1972;101(4):626–37.
3.
Grande M, Murua H, Zudaire I, Goni N, Bodin N. Reproductive timing and reproductive capacity of the Skipjack Tuna (Katsuwonus pelamis) in the western Indian Ocean. Fisheries Research. 2014;156:14–22.
4.
Maunder MN, Harley SJ. Status of skipjack tuna in the eastern Pacific Ocean in 2003 and outlook for 2004. Inter-Amer Trop Tuna Comm, Stock Assessment Report. 2005;5:109–67.
5.
Stéquert B, Rodriguez JN, Cuisset B, Le Menn F. Gonadosomatic index and seasonal variations of plasma sex steroids in skipjack tuna (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) from the western Indian ocean. Aquatic Living Resources. 2001;14(5):313–8.
6.
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.