page_title: Bluefin trevally
section_title: Life history
hierarchical_section_title: Bluefin trevally / Biology and ecology / Life history
caption_attribution_description: English: Flickr tool output Description bluefin trevally Date28 June 2006, 06:50Sourcebluefin trevallyAuthorjon hanson from London Licensing This file is licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license. You are free: to share – to copy, distribute and transmit the work to remix – to adapt the work Under the following conditions: attribution – You must attribute the work in the manner specified by the author or licensor (but not in any way that suggests that they endorse you or your use of the work). share alike – If you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one. This image was originally posted to Flickr by jon hanson at https://www.flickr.com/photos/61952179@N00/193666788. It was reviewed on 12 October 2009 by FlickreviewR and was confirmed to be licensed under the terms of the cc-by-sa-2.0. bluefin trevally
context_page_description: The bluefin trevally, Caranx melampygus, is a species of large, widely distributed marine fish classified in the jack family, Carangidae. The bluefin trevally is distributed throughout the tropical waters of the Indian and Pacific Oceans, ranging from Eastern Africa in the west to Central America in the east, including Japan in the north and Australia in the south. The species grows to a maximum known length of 117 cm and a weight of 43.5 kg, however is rare above 80 cm. Bluefin trevally are easily recognised by their electric blue fins, tapered snout and numerous blue and black spots on their sides. Juveniles lack these obvious colours, and must be identified by more detailed anatomical features such as fin ray and scute counts. The bluefin trevally inhabits both inshore environments such as bays, lagoons and shallow reefs, as well as deeper offshore reefs, atolls and bomboras. Juveniles prefer shallower, protected waters, even entering estuaries for short periods in some locations.
  The bluefin trevally is a strong predatory fish, with a diet dominated by fish and supplemented by cephalopods and crustaceans as an adult.
context_section_description: The bluefin trevally reaches sexual maturity at between 30 and 40 cm in length and around 2 years in age,
  with one study Hawaii suggesting maturation occurs at a length of around 35 cm on average.  There is also a difference in the length at maturation between the two sexes, with females on average reaching maturity at 32.5 cm length, while males attain maturity at 35 cm on average. Sex ratios in the species vary by location with population off east Africa being skewed towards males (M:F = 1.68:1), while in Hawaii the opposite is true with the M:F ratio being 1:1.48. The period of the year over which spawning occurs is also variable by location, with African fish reproducing between September and March while in Hawaii this occurs between April and November, with a peak in May to July. Natural spawning behaviour in the species has never been observed, although large aggregations of bluefin trevally observed in Palau consisting of over 1000 fish are believed to be for the purpose of spawning. Extensive studies on the species in captivity has revealed the species to be a multiple spawner, capable of spawning at least 8 times a year, and up to twice in 5 days. Spawning events are often clustered in a few consecutive or alternate days, usually in the third or fourth lunar phases. Spawning apparently occurs at night to minimise predation on eggs. Fecundity in the natural environment has been reported to range from around 50 000 to  4 270 000, with larger individuals releasing more eggs. Studies in captive fish show females may produce over 6 000 000 eggs per year. These eggs are pelagic and spherical, with diameters between 0.72 and 0.79 mm.
  The development of the bluefin trevally larvae after hatching has been briefly described in a study of changes in the digestive enzymes of the species. The species has depleted its storage of energy from the egg at 3 days old, with a series of transformations including coiling of the gut and fin formation occurring before flexion at 26 days of age. Digestive enzymes active from hatching to 30 days old show an apparent shift from carbohydrate utilisation to protein and lipid utilisation as the larvae grows older. Measurements from juveniles in Hawaii indicate the fish is around 70 mm by 100 days and 130 mm by 200 days. Otolith data fitted to the von Bertalanffy growth curve shows the species grows to 194 mm in its first year, 340 mm in the second and 456 mm in the third year. It reaches 75 cm by 8 years of age and 85 cm by 12 years.  This model also suggests a growth of 0.45 mm/day; while laboratory feeding studies found the fish grow at an average of 0.4 mm/day in these confined conditions. The maximum theoretical size indicated from the growth curves is 89.7 cm,  much less than the 117 cm reported as the known maximum size. Juveniles often enter estuaries, however the species is not estuary dependent as breeding is known to occur where no estuaries are present, suggesting the use of these habitats is facultative. The fish move from these shallower inshore waters to deeper reefs as they grow.
  Two hybridisation events in the species are known from Hawaii; the first with the giant trevally, Caranx ignobilis and the second with the bigeye trevally, Caranx sexfasciatus. Both were initially identified as hybrids by intermediate physical characteristics, and were later confirmed by DNA sequencing. It has been suggested these hybrids resulted from mixed species schooling during spawning periods. It is thought that hybridisation is more likely if one or both parent species is rare in an area, which is the case in much of the Main Hawaiian Islands, where overfishing has severely depleted all trevally species populations.
caption: It takes 12 years for a bluefin trevally to reach 85 cm in length
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