Why being fish-shaped is the ultimate energy hack of the ocean
The classic fish-shaped body — a squashed teardrop with a pointed nose and tapered tail — has evolved time and again.
There are tuna with the classic fish shape, sharks, marlin, mackerel and thousands of other species that spend a lot of time swimming.
The reason it’s so common comes down to the fact that water is around 800 times denser than air, and much stickier, which means it takes far more energy to move through it. You can feel the difference, when swishing your hand through water compared to air.
Being fish-shaped, or ‘fusiform’, allows a body to cut through the water while creating minimal drag. This is the best energy-saving shape for swimming animals, including not just fish, but also dolphins, whales, and extinct ichthyosaurs.
Other components of the classic fish shape are the fins, in particular the tail or ‘caudal fin’, which swishes from side to side to create propulsion. Fish with different swimming habits have differently shaped caudal fins. Tuna and other fast swimmers tend to have a forked or crescent-shaped tail which is good for long-distance, endurance swimming. Fish such as groupers and barracudas have much wider caudal fins, which are harder work to push through the water but excellent for putting on quick bursts of speed when they ambush prey over short distances.
Of course, there are many ways of being a fish and not all are superb swimmers. Many other body shapes have evolved among slow and sedentary fish, from S-shaped seahorses to four-legged frogfish and square boxfish.
- Do fish sleep?
- How do fish know who they are?
- Why do fish have vertical tail fins and whales have horizontal ones?
- Can fish see in the dark?
Every week on BBC World Service, CrowdScience answers listeners’ questions on life, Earth and the Universe. Tune in every Friday evening on BBC World Service, or catch up online at bbcworldservice.com/crowdscience
To submit your questions email us at firstname.lastname@example.org (don't forget to include your name and location)
- Try your first 6 issues for just £9.99 when you subscribe to BBC Science Focus Magazine.
- Risk - free offer! Cancel at any time when you subscribe via Direct Debit.
- FREE UK delivery.
- Stay up to date with the latest developments in the worlds of science and technology.