Bluefin Trevally: a two-minute wildlife lesson

Coral Reef · day 6 of 7

Five facts

1. Each adult bluefin trevally swallows about 45 kg of fish a year, making it one of the most efficient predators on coral reefs.
2. Adult bluefin trevallies eat almost only fish, over 95 % of stomach contents by weight. Juveniles in Hawaiian estuaries eat almost only crustaceans.
3. Adult bluefin trevallies mostly live alone, but they gather to spawn or hunt. Lab tests suggest a reef chemical, DMSP, helps them group up.
4. In captivity, a bluefin trevally can spawn up to eight times a year, releasing up to six million eggs in that year.
5. Bluefin trevallies grow fast: 194 mm in year one, 340 mm in year two, 456 mm by year three.

The quiz

1. About how much fish does an adult bluefin trevally swallow per year?

• About 4 kg
• About 45 kg (correct)
• About 14 kg
• About 450 kg

Each adult swallows about 45 kg of fish per year.

2. What do juvenile bluefin trevallies in Hawaiian estuaries eat almost exclusively?

• Crustaceans (correct)
• Fish
• Seaweed
• Jellyfish

Juveniles in Hawaiian estuaries eat crustaceans almost exclusively.

3. According to lab tests, what may help bluefin trevallies gather over reefs?

• Loud clicking sounds
• Flashing colours
• A reef chemical called DMSP (correct)
• Body heat

Lab tests suggest that DMSP released by the reef helps them gather.

4. How many times a year can a bluefin trevally spawn in captivity?

• Only once
• Up to three
• Up to twenty
• Up to eight (correct)

In captivity they can spawn up to eight times a year.

5. How long is a bluefin trevally by the end of its third year?

• 456 mm (correct)
• 194 mm
• 340 mm
• 117 mm

It reaches 456 mm by the third year.

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