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Ulua Species Information

Information Provided by Pacific Islands Fisheries Group

Species in General

Ulua, otherwise known as the Giant Trevally  is a member of the jack family, Carangidae. Uluas are found throughout the tropical waters as far as Africa, through the Pacific Ocean, Hawaii, Japan, and Australia. The species can inhabit a wide range of environments including, bays, reefs, lagoons, rivers, atolls, deep channels, and shorebreaks. Uluas are an apex predator which feed on fish, eels, octopus, crabs, and other live prey.

 

According growth charts 100lb plus size Uluas are said to be approx. 25 years old and some speculate they could even be as old as 100 years. One of the ways to age fish is by collecting and analyzing their otoliths. In the center of each ulua/papio head there is a chamber which houses the inner ear bone called the otolith. Fin fish have 3 sets of otoliths. The first (largest of the three) is called the sagittae, the second is the asterisci and the third (smallest) is the lapilli. “Fish otoliths accrete layers of calcium carbonate and gelatinous matrix throughout their lives. The accretion rate varies with growth of the fish often less growth in winter and more in summer which results in the appearance of rings that resemble tree rings. By counting the rings, it is possible to determine the age of the fish in years.”

 

Red arrow indicates location of where the otolith chamber is located within the White Ulua’s head. Rough cutting is necessary in order to gain access to the otolith.

Left - 95 lb Ulua / Middle - 100.3 lb Ulua / Right - 145 lb Ulua

The three sets of otoliths after being removed from the White Ulua Head. The otoliths will be sectioned and analyzed to

determine age of the ulua.

Gender & Reproduction

Visually there is no way of telling what sex your ulua or papio maybe, but there are some anecdotal information. As noted from samples of eggs collected from ulua/papio by field personal the coloration of males tended to be very dark in coloration in the case of white ulua almost completely black. The white ulua males body tended to appear longer and not as deep as the female. For the omilu the same the traits tended to be similar to the white ulua males in that the males were very dark. More samples will need to be collect to see if these observations run true. Also some fishermen say that the pectoral fin on the female white ulua tend to be longer than the male. In order to prove these observations true or false we will need many samples (photos) and confirmation of sexual orientation of the ulua/papio.

Males

Position of Reproductive Sac within the White Ulua stomach cavity

Females

Male Omilu - Note the white coloration of sac

Female Omilu - Note the red veins surrounding yellow egg sac

Male White Ulua - Note the white coloration of sac

Female White Ulua - Note the red veins surrounding yellow egg sac

Ulua, Omilu, and Papio Travel within the Hawaiian Islands

Age & Growth

Another way of aging fish is called radio carbon or carbon dating. Carbon-14 dating is a way of determining the age of certain archeological artifacts of a biological origin up to about 50,000 years old. It is used in dating things such as bone, cloth, wood and plant fibers that were created in the relatively recent past by human activities. This method is very expensive to perform, but can be used to help validate otolith readings or when otoliths are difficult to read.

Age, growth and maturity studies of fish are important for understanding such things as timing of spawning, recruitment, larval and juvenile duration, and population age structure. Such knowledge is in turn important for designing appropriate fisheries management policies.

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