Field notebook
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Taxonomic class
This practical browse label comes from the published animal profiles. Taxonomy changes as evidence improves; individual source records remain the authority.
Atlantic mudskippers spend most of their active hours out of water, absorbing oxygen through their skin and mouth lining rather than relying only on gills, a trait called cutaneous respiration.
Humphead parrotfish bite living coral, grind the skeleton in a throat mill of interlocking teeth, and excrete the rock as fine white sand. Estimates for large individuals run to several tonnes per fish per year.
Most bony fish carry a gas-filled float that holds them at depth without effort. Atlantic mackerel do not have one, so they must swim continuously to avoid sinking, and can change depth quickly without waiting for gas to equilibrate.
The family is named for a two-spine mechanism in the dorsal fin. The first spine raises and a smaller second spine slots in behind it as a locking pin, wedging the fish inside a hole so it cannot be pulled out.
Anemonefish are protandrous hermaphrodites. The largest fish in an anemone is female, the second largest is her mate, and when she dies her partner changes sex to replace her rather than a new female arriving.
Behind the walleye's retina sits a reflective layer called the tapetum lucidum, which bounces light back through the light-sensing cells. It gives the fish its glassy shine and a hunting advantage in low light that its prey does not share.
Snailfishes have been collected from about 8,000 metres in the Mariana Trench, and since 2022 both filmed and caught deeper still off Japan. Those depths sit close to the point at which fish physiology is predicted to fail.
The arapaima shares its water with piranhas and wears armour to match. Its scales are layered composites with a hard mineralised outer surface over tough, twisted collagen, and mechanical tests show piranha teeth fracture before the scale does.
Two rays of the pelvic fins and one of the tail are elongated and stiffened into struts. The fish rests on them above the sediment, facing into the current, and holds its long pectoral fins forward like antennae.
Canada closed the northern cod fishery in 1992 expecting a two-year pause. More than three decades later the stock remains far below its historical size, and the ecosystem around it reorganised in ways that appear to hold cod down.
Zanclus cornutus is the sole living member of the family Zanclidae. Its nearest relatives are the surgeonfish, and a distant butterflyfish, the pennant coralfish, carries such a similar banded outline that the two are constantly mistaken for each other.