Clown anemonefish, iconic residents of coral reefs, are now known to physically shrink to survive. A new study in Science Advances monitored 134 clownfish in Papua New Guinea during a 2023 marine heatwave and found that over 70 percent of individuals shrank at least once during the five-month event.

The Marine Conservation Society (MCS) has downgraded mackerel from a sustainable seafood choice to a cautionary amber rating, urging consumers to switch to herring or Cornish sardines instead. 

This groundbreaking research documents the behaviour in several oceanic fish species spanning three oceans. It describes the first recorded instances of fish using sharks and other fish to brush and scrape against, with the goal of freeing themselves of parasites.

The Hades’ snake moray (Uropterygius hades) is a slender, dark brown eel which stands out for its unique adaptations to and preference for dim, turbid environments.

Unlike most of its marine relatives, which thrive in coral reefs, it is at home in estuarine habitats, a characteristic that is unusual among the 230 known species of moray eels. It is distributed across the Central Indo-Pacific, and has been found in southern Japan, Taiwan, the Philippines, southern Java, and Fiji.

In a recent study, researchers investigated how sardines that find themselves on a predator's radar collectively employ collective evasive manoeuvres and how their predators respond to outsmart them.

Using computational modelling and aerial video footage, the team from the Cluster of Excellence “Science of Intelligence” (SCIol), the Humboldt-Universität zu Berlin, the Leibniz Institute of Freshwater Ecology and Inland Fisheries, and Cambridge University focussed on the predator-prey behaviour of striped marlins and sardine shoals in the open ocean. 

When it comes to making its grand entrance into the world, fish embryos do not leave things to chance.

Researchers, led by Dr. Matan Golan of the Hebrew University of Jerusalem and the Agricultural Research Organization-Volcani Institute, have discovered that the hatching process of fish embryos is not a passive process. 

Several times a year, squaretail groupers gather at spawning aggregation sites to mate, typically around the new and full moons between December and March. The males show up several days before to establish their territories, while the females arrive a day before the new moon. Then, both groups will attempt to pair and spawn in synchrony with the moon’s cycles.

For this species, these brief encounters are their only opportunities to reproduce.

Clownfish, also known as anemonefish, are feisty critters that vigorously defend their anemone homes from intruders, particularly those of their own species, displaying aggressive behaviour. Anemonefish species living in the same areas exhibit a variety of stripe patterns, ranging from three vertical bars to none, as observed by Kina Hayashi from the Okinawa Institute of Science and Technology, Japan.