Tuna or Mackerel

Yellowfin tuna (Tom Wang / shutterstock.com)

Tunas and mackerels constitute the family Scombridae. Members of this family have streamlined bodies, 2 dorsal fins, 5 to 12 finlets, and deeply forked caudal fins with at least two keels. The pelvic fins are located below the pectoral fins. Tunas are excellent swimmers, reaching a top speed of about 75 kilometers (47 miles) per hour. Size varies greatly among the different species, ranging from 35 centimeters (14 inches, long-jawed mackerel) to 4.2 meters (13.8 feet, bluefin tuna) in length. Due to commercial fishing pressure, the bluefin tuna is classified as endangered on the IUCN Red List.

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This supplemental online resource accompanies the book Scuba Diving Hand Signals by Lars Behnke, available on Amazon.